Carpentry. FRMG 202/222 Roof Framing

Transcription

1 Carpentry FRMG 202/222 Roof Framing

2 Copyright Saskatchewan Institute of Applied Science and Technology No part of the work(s) contained herein may be reproduced or copied in any form or by any means - graphic, electronic, or mechanical, including photocopying, recording, taping of information and retrieval systems - without written consent of the Saskatchewan Institute of Applied Science and Technology. Used With Permission Engineered roof trusses. Courtesy of Gang-Nail: Pilot Butte, Saskatchewan.

3 FRMG 202/222 Roof Framing Course Overview Course Description Learning Outcome(s) Course Hours Assessment of Learning Outcome(s) This course is designed to provide the carpenter apprentice with the theory and skills to construct and install conventional gable and hip roofs and install gable roof trusses. 1. Construct Conventional Gable and Shed Roofs 2. Construct Conventional Hip Roofs 3. Assemble Engineered Roof Trusses and Install Sheathing 4. Frame a Gable and Hip Roof Using Metric Measurements 48 hours Knowledge Assessment Your knowledge of roof framing will be assessed by means of a written exam worth 50% of the course grade. Passing Grade 60% Performance Assessment Your practical skills will be assessed by means of the following performance test(s) worth 50% of the course grade: Construct a Gable Roof (10%) Construct a Hip Roof (10%) Lay Out a Common Rafter, Collar Tie, and Gable End Stud (15%) Lay Out a Hip Rafter, a Hip Jack, and a Ridge (15%) Lay Out for Roof Trusses and a Gable End Overhang Resource(s) to Purchase Saskatchewan Institute of Applied Science and Technology. (2012). FRMG 202/222 Roof framing [Course Manual]. Prince Albert, SK: SIAST Woodland Campus. Kesik, T. J., & Lio, M. (2005). Canadian wood frame house construction. Ottawa, ON: Canada Mortgage and Housing Corporation. National Building Code of Canada. (2010). National Building Code of Canada/issued by the Canadian Commission on Building and Fire Codes, National Research Council of Canada (NRCC ed.). Ottawa, ON: National Research Council of Canada Institute for Research in Construction. Vogt, F., & Nauth, M. (2009). Carpentry (1st Canadian ed.). Toronto, ON: Nelson Education Ltd. i

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5 Table of Contents Learning Outcome 1 Construct Conventional Gable and Shed Roofs Learning Step 1: Identify the Various Types of Roofs and Roof Terminology... 1 Learning Step 2: Perform Gable Roof Calculations... 6 Learning Step 3: Layout and Cut a Ridge and a Common Rafter Learning Step 4: Determine Rafter Sizes and Support Systems for Gable Roofs Learning Step 5: Lay Out and Construct Gable End Studs, Gable Ends, and Gable Roof Ladders Performance Test 1: Construct a Gable Roof Learning Step 6: Calculate and Lay Out a Shed Roof Rafter Performance Test 2: Lay Out a Common Rafter, Gable End Stud, Ridge Board, and Collar Tie Learning Outcome 2: Construct Conventional Hip Roofs Learning Step 1: Calculate and Lay Out the Ridge Board and Hip Rafters Learning Step 2: Calculate and Lay Out Hip Jack Rafters and Assemble Hip Roof Components Performance Test 3: Construct a Hip Roof Performance Test 4: Lay Out a Hip Rafter, Hip Jack, and Ridge Learning Outcome 3: Assemble Engineered Roof Trusses and Install Sheathing Learning Step 1: Identify Types of Roof Trusses and List Advantages of Using Trusses Learning Step 2: Install Roof Trusses Performance Test 5: Lay Out Roof Trusses Learning Outcome 4: Frame a Gable and Hip Roof Using Metric Measurements Learning Step 1: Perform Gable Roof Calculations in Metric Measurements Learning Step 2: Perform Hip Rafter Calculations Using Metric iii

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7 Learning Outcome 1 Construct Conventional Gable and Shed Roofs Learning Step 1 Identify the Various Types of Roofs and Roof Terminology 1.1 Reading Assignment Study the following: from the textbook, Carpentry, read the chapters on "Roof Types and Terms" and "Gable and Gambrel Roofs" from the textbook, Canadian Wood-Frame House Construction, read "Framing the House" - Ceiling and Roof Framing 1.2 Instruction Sheet Types of Roofs One of the most essential components of a house is the roof. The roof not only provides protection against the weather, but also forms a structural tie between outside walls. The illustrations below show most of the roof shapes that have been used over the years, each with its own unique appearance and advantages. Figure 1: Types of Roofs FRMG 202/222 Roof Framing LO1 Page 1

8 Flat Roof (Figure 1a) These are constructed with roof joists which support the roof as well as the ceiling. They have a minimal slope for drainage. Flat roofs vary from flat to a slope of 3 in 12 (250 in 1000). Shed Roof (Figure 1b) These roofs have only one sloped surface which is normally across the width of the building. This is one of the simplest roof types to construct. Gable Roof (Figure 1c) Gable roofs have two sloped surfaces meeting at a ridge. At each end of the roof a gable is formed. These are one of the most popular types of roofs. Hip Roof (Figure 1d) The hip roof is sometimes referred to as a cottage roof. They have four sloped surfaces meeting at the ridge. Hip and Valley Roof (Figure 1e) These are sometimes referred to as intersecting roofs. This type of roof forms a valley at the intersection of two sloped surfaces. The ridges of the two roof sections usually form a 90 corner. Gable Roof and Dormer (Figure 1f) This is a gable roof with one or more dormers projecting from one or both sides of the main roof. The dormers bring light into a second story room. Gable and Valley Roof (Figure 1g) This is another intersecting roof. Two gable roofs meet to form an intersecting valley. Mansard (Figure 1h) This roof is a variation of the hip roof. The roof has steep slopes on all four sides which meet and form a second flatter level. Butterfly Roof (Figure 1i) This is basically an inverted gable roof. Gambrel Roof (Figure 1j) This is a variation of the gable roof, also called the barn roof. It has steep slopes on the two sides. Part of the way up, the second flatter slopes begin. These two slopes meet in the centre of the building. FRMG 202/222 Roof Framing LO1 Page 2

9 Dutch Hip (Figure 1k) This is a hip roof with a small projecting gable at the ridge. In the true dutch hip roof, the barge rafters at the rake slope outward from the ridge. 1.3 Instruction Sheet Roof Framing Components In order to perform roof framing calculations, and to lay out and construct different styles of roofs, you must first be able to recognize and define the terms involved. Following is a list of the terms you will be required to know. Gable Roofs Definition of Terms While you are studying the following definitions refer to Figures 2 and 3. rafter plates - the plates on which the rafters rest and support the weight of the roof. These plates are most often the double plates on top of the exterior walls as in Figure 2, but with today's energy efficient trends, it is common to use a rafter plate as shown in Figure 2, detail "A," in order to allow more insulation at the perimeter of the attic. common rafter - the roof framing member that extends in one piece from the rafter plate to the ridge at 90 to the plate (in plan view), and often extends beyond the rafter plate to form the overhang ridge board - a horizontal member at the top of the roof which aligns the rafters during erection, and provides backing for the roof sheathing rafter tail - that portion of the rafter that extends out from the rafter plates to form the overhang rough fascia - a horizontal member nailed to the rafter tails to align them, and to provide backing for the soffit and finish fascia finish fascia - usually thinner than the rough fascia, provides a finished appearance, and usually consists of wood, metal, or vinyl overhang - the total horizontal projection of the rafter tail which forms the eaves of the building. The overhang includes the fascia. plumb cut - a cut on the rafter that is vertical when the rafter is in place seat cut - the horizontal cut that is level when the rafter is in place. The seat cut of the rafter rests on the rafter plate. birdsmouth - a combination of a seat cut and a plumb at the point where the rafter rests on the rafter plate. A seat cut and a plumb cut form a 90 angle. tail cut - the plumb cut at the tail-end of the rafter gable stud - the studs that frame the exterior walls at the gable ends of a gable roof FRMG 202/222 Roof Framing LO1 Page 3

10 collar tie - a horizontal member that is fastened to two opposite rafters to give additional support to the rafters, thus reducing their unsupported span and sometimes allowing a lighter rafter to be used. These are sometimes called collar beams. barge rafter - similar to the rough fascia, but placed on the outer edge of the overhang on the gable (rake). The length of the barge rafter is the same as the length of the common rafter including the rafter tail. The barge rafter is usually supported by lookouts along its length, and besides forming the overhang, acts as backing for the soffit. The barge rafter is sometimes covered with a finish fascia (see Figure 3). lookouts - usually 2 4's, sometimes cantilevered over the gable to support the barge rafters, and to act as backing for the soffit. Lookouts also extend from the walls to the fascia for soffit backing (see Figure 3). gable - that portion of wall immediately below the two opposite sloping rafters on the end of a gable roof. It is framed with gable studs and is triangular-shaped (see Figure 3). Figure 2: Roof Components Figure 3: Roof Components FRMG 202/222 Roof Framing LO1 Page 4

11 Flat Roof Construction The following illustration shows the framing of a flat roof including the overhang. Intersecting Roofs Figure 4: Flat Roof Intersecting roofs will be covered in another course manual in Level 4. If you are interested in intersecting roofs, read "Intersecting Roofs" in the textbook, Carpentry. 1.4 Review Exercise Identify the following roofs by placing the appropriate letter for the terms in Column B on the line beside the correct definition in Column A. You may use the items in Column B more than once. Column A 1. A roof which has a single slope on two sides, meeting at the ridge. 2. A roof having a single slope on four sides. 3. A roof having two slopes on two sides. Column B a. gable b. butterfly c. shed d. hip e. mansard f. gambrel 4. A roof having two slopes on four sides. 5. A roof sloping in one direction only. 6. Two shed roofs sloping upward from the eaves meet, forming a ridge. 7. Two shed roofs sloping downward from the eaves to a low point near the centre of the building. 8. A style of dormer roof. FRMG 202/222 Roof Framing LO1 Page 5

12 9. Name the gable roof parts in following figure. Figure Learning Step 2 Perform Gable Roof Calculations 2.1 Instruction Sheet Roof Slopes The roof slope is the angle of the roof in relation to the horizontal wall plates. A roof slope may be expressed in 1. degrees, 2. a ratio, or 3. as a percentage. Ratios are the most common way of expressing roof angles. FRMG 202/222 Roof Framing LO1 Page 6

13 Slopes are expressed as a ratio of rise to run, rise being vertical, and run being horizontal. The rise (vertical) number of the ratio must always be given first, the run (horizontal) number given last. It is standard practice in the imperial system of measurements to express roof slopes as inch per foot run ratio. (For example: 4 inch rise per 1 foot run is read as 4 inch to 12 inch, or 4 to 12.) Roof Slope Symbol The roof slope symbol is often shown on a blueprint as a small right angled triangle slightly above the roof line. The symbol shows the amount the roof rises for every 12 inches of horizontal distance. This symbol represents 1 unit of the roof mathematics. Figure 6: Roof Slope Symbol In the above figure, the roof rises 4 inches (unit of rise) for every 12 inches of horizontal distance (unit of run). Unit of Run The unit of run for a common rafter is always 12 inches. Unit of Rise The unit of rise is the amount the roof rises per foot of run. The unit of rise changes as the roof slopes changes. Unit of Line Length The unit of line length is the length of the hypotenuse of the roof slope symbol (the line that connects the unit of rise and unit of run). The length is found on the framing square so it doesn't have to be calculated mathematically each time it is needed. FRMG 202/222 Roof Framing LO1 Page 7

14 Ratio Figure 7: Roof Unit Triangle A ratio is a relationship between two numbers or values. A 1 in 3 ratio can also be written as 1:3, and is read as "one is to three" or just "one to three." A 1 in 3 roof slope means the unit of rise in one and the unit of run is three. Figure 8: Roof Slope 1 in 3 The unit of run is always 12 inches, so proportioning must be calculated. Proportioning A proportion is a method of expressing equality between two ratios. An example proportion is as follows: One side is equal to the other (each side equals one-half). To change a 1:3 ratio to a roof slope based on a 12 inch unit of run, set up a proportion as follows: 1:3 is written 1 3 so 1 Unknown Rise(R) 3 12 inches FRMG 202/222 Roof Framing LO1 Page 8

15 1 R 3 12 To find R (rise) we cross multiply, that is we multiply the top number on one side of the equal sign with the bottom number on the other side = 3 x R 12 = 3R 12 R 3 Rise = 4 inches Therefore a 1:3 ratio is the same as 4 12 roof slope. 2.2 Review Exercise Convert the following roof slope ratios to rise per foot of run. Round off your answer to the nearest quarter inch (.25"). 1. 1:4-2. 1:2-3. 1:6-4. 1:1-5. 1: : Instruction Sheet Common Roof Geometry To determine the exact line length of the common rafter is an important task that carpenters must perform. This may be done mathematically or with a steel rafter framing square. In North America, a steel rafter framing square is traditionally used, so a thorough knowledge of determining line lengths using a steel square must be mastered. Calculate Measurements Total Run Two rafters cover the span of the "roof." The "span" of the rafter is the total run of the roof. The total run of one common rafter is equal to the horizontal distance the rafter spans. This is half the width of the building with an equal sloped roof. FRMG 202/222 Roof Framing LO1 Page 9

16 The total run is measured horizontally from the outside of the wall plate or rafter plate, to the centre of the building. Figure 9: Total Run of Rafter The common rafter has a total run of 14'-0", or it can be said the rafter spans 14'-0". The span of the roof is 28'-0". Total Rise of a Roof So far we have talked about the unit of rise, now we will describe the total rise of the roof. The total rise of a roof is vertical distance from the top of the wall plate to the intersecting point of the theory lines of the common rafters, at the ridge. Figure 10: Total Rise of a Roof To calculate the total rise of a roof multiply the number of units of run for the rafter times the unit of rise (from the roof slope symbol). Units of Run of Rafter = 28'-0" 2 = 14' or 14 units of run Total Rise = 14 4 = 56" or 4'-8" (The building is 28 feet wide; therefore, the rafter spans one-half this distance, or 14'-0".) Actual Rise The actual rise of the roof is the Total Rise Plus the Height of Rafter Above the Birdsmouth (see Figure 11). This measurement is measured with your pocket tape when laying out the rafter. FRMG 202/222 Roof Framing LO1 Page 10

17 Figure 11: Actual Rise The Roof Triangle Note that the components mentioned so far form a right triangle, with the total run as base, the total rise as altitude and the theory line of the common rafter forming the hypotenuse. Any roof can be broken down into these simple right triangles for calculations. Note: The line length of a common rafter is the measurement from the plumb cut at the birdsmouth to the point where the theory lines intersect at the ridge (see Figure 10), measured along the theory line. The right triangle is the whole basis of roof framing. Therefore the line length of the common rafter is as follows: ' To change.757 back to inches, first multiply the decimal portion by 12 to get inches, and then the decimal part of that answer by 16 to get sixteenths..757' 12 = inches.084" 16 = 1.34 sixteenths So ' is the same as 14" " FRMG 202/222 Roof Framing LO1 Page 11

18 Figure 12 Unit Triangle The basic roof triangle as outlined may be reduced proportionally into a "unit triangle" whose base is the "unit of run," altitude the "unit of rise," and the hypotenuse the "unit of line length." Note: That the "roof triangle" has as many "unit triangles" as it has "units of run." In the following figure, the roof has 4 units of run. Also, it must have 4 units of rise and 4 units of line length, or 4 complete unit triangles. Figure 13 Line Length of a Common Rafter Calculated Using Square Root It is sometimes necessary to calculate the line length of the common rafter using the square root method because the tables on the framing squares are not large enough to have all possible roof slopes on them. FRMG 202/222 Roof Framing LO1 Page 12

19 The square root method uses the Pythagorean Theorem to calculate the line length of a rafter. This theorem, named for the ancient Greek mathematician, Pythagoras, states that in any right angle triangle, the square of the longest side is equal to the sum of the squares of the other two sides: c 2 = a 2 + b 2 where c = hypotenuse, a = altitude (height), and b = base. (see Figure 12) The length of the hypotenuse, c, is equal to the square root of the sum of the squares of the other two sides: Hypotenuse c a b If we compare the line length of a common rafter to the hypotenuse of a right angle triangle, then the total rise will be the altitude and the total run of the rafter will be the base of the triangle. Now, we can write the following: Rule: Line Length of Common Rafter = total rise total run 2 2 Example: total run = 14'-0"; total rise = 4'-8" Before we go any further we must change the 8 inches in 4'-8" to a decimal so we can multiply easier. 8 inches is 8 12 of a foot, so divide 8 by 12, which gives us.6666'. So now 4'-8" can be changed to ' or 4.67'. Unit Line Length (U.L.L.) Using the Unit Triangle The length of the hypotenuse of the unit triangle may be also calculated by square root. For example, using a 4 12 Roof slope Hypotenuse "or ", the unit of length This unit of line length may also be found on the rafter tables on the steel square (see Figure 14). On the body of the square find "Length of Common Rafters Per Foot Run." Next find the unit of rise on the numbers along the outside edge of the square. Our sample uses a 4 inch unit of rise, so the 4 inch mark on the square (see Figure 14). Under the 4 inch number, read the unit of line length, The decimal isn't shown, just a space where the decimal goes. FRMG 202/222 Roof Framing LO1 Page 13

20 Figure 14: Imperial Framing Square Therefore the line length of this common rafter is inches per foot of run. Line Length of a Common Rafter Using Rafter Tables To find the line length (L.L.) of the common rafter, multiply the number of units of run times the unit of line length. Rule: Line Length of Common Rafter = Number of Units of Run U.L.L. From Framing Square Example: Building 28'-0" wide Gable roof 4 12 Roof slope L.L. Common Rafter = Number of Units of Run U.L.L. = " = 177.1" = 14'-9 ⅛" Deduction for the ridge board will be covered later. Common Rafter Tail The rafter tail is calculated separately, even if it is part of the same rafter stock. Calculating the line length if the rafter tail is similar to the common rafter. First determine the run of the rafter tail and how many units of run are in the rafter tail. If the overhang on a building is 24 inches, the tail has a 2 foot run or 2 units of run. If the roof is a 4 12 slope multiple 2 units of run U.L.L. (from framing square) = " = 25.3 inches = 2' " FRMG 202/222 Roof Framing LO1 Page 14

21 If the overhang isn't in even number of units of run, you still can calculate the L.L. of the tail. For example, if we had a 16 inch overhang using as 5 12 slope, the rafter tail would be calculated as follows (see Figure 15): Unit line length = 13", number of units of run = " = 1.33 Line length of rafter tail = unit line length x number of units of run = 13" 1.33 = 17.29" = 1' " Deduction for the rough fascia will be covered later. The Framing Square (Imperial) Figure 15: Line Length of Overhang The following figure shows the framing square with the roof framing tables. The square is used for calculating line lengths not only of common rafters, but for hips, valleys, and jacks. FRMG 202/222 Roof Framing LO1 Page 15

22 2.4 Review Exercise Figure 16: The Imperial Framing Square (Using a Unit of Run of One Foot or 12 inches) 1. Given in the chart below, the total rise and total run of a rafter, calculate their line lengths using square root. Total Rise Total Run Line Length a. 7'-0" 16'-0" b. 3'-6" 12'-0" c. 6'-0" 15'-6" d. 4'-4" 13'-0" e. 2'-3" 10'-5" 2. A roof with a span of 20 feet and a unit-of-rise of 8 inches would have a total rise of: FRMG 202/222 Roof Framing LO1 Page 16

23 3. Calculate the line length of a common rafter for a building 22 feet wide and a 8 12 slope. 4. What is the line length of a rafter tail for a 16 inch overhang using a 3 12 slope? FRMG 202/222 Roof Framing LO1 Page 17

24 a b c d e f g h i j k l Slope Ratio 1:3 1:2.4 1:1.71 1:2 1:4 1:1.5 1:3 1:1.33 1:2.4 1:1.2 1: Span of Roof 32'-0" 26'-0" 24'-0" 30'-0" 28'-0" 26'-0" 24'-0" 28'-0" 30'-0" 27'-0" 25'-0" 28'-0" Run of Rafter Number of Units of Run Unit of Rise Unit of Line Length Line Length of Rafter Overhang Projection 2'-0" 1'-6" 1'-0" 2'-0" 1'-4" 1'-0" 1'-4" 1'-6" 2'-0" 1'-4" 1'-0" 1'-3" Line Length of Overhang Total Rise of Roof 5. Using the steel square rafter tables and performing the necessary calculations, fill in the blanks for the following common rafters. FRMG 202/222 Roof Framing LO1 Page 18

25 Learning Step 3 Layout and Cut a Ridge and a Common Rafter 3.1 Reading Assignment Study the following: from the textbook, Carpentry, review the chapters "Roof Types and Terms" and "Gable and Gambrel Roofs" from the textbook, National Building Code of Canada, study section on "Roof and Ceiling Framing" 3.2 Instruction Sheet Laying Out a Ridge and a Common Rafter Ridge Board A ridge board is a board at the peak of a roof to which the tops of rafters are nailed. A roof may be framed without a ridge board, but the ridge board helps to maintain spacing and alignment of rafters at the top. Common thickness of ridge boards are ¾ inch and 1½ inches. The NBC states the ridge board must be a minimum of 17.5 mm thick. The depth of the ridge board is usually one size larger stock than the rafter stock, so that the plumb cut of the common rafters have full bearing at the top. So if we are using 2 4, we would use a 1 6 or 2 6 ridge board. Ridge boards must be joined on a rafter centre. The theory length of a ridge board for a gable roof is equal to the length of the building plus overhang at each end (see Figure 17). The cutting length of the ridge may be 1½ inches less at each end to allow the barge rafters to butt together without the ends of the ridge board showing. FRMG 202/222 Roof Framing LO1 Page 19

26 Figure 17: Ridge Board Length After the rafter lay out has been marked onto the top of the wall plates, the ridge board should be placed beside the plate so the lines can be transferred from the plate to the ridge.this ensures the rafter locations will be exactly the same on both the plates and the ridge. Figure 18: Layout of Rafters on Ridge Board Sometimes the ridge board requires notching at the ends, on the overhangs. If the soffit is to be finished with plywood on the underside, the ridge board must be made the same width as the rafters, or else it will hang below the plywood finish (see Figure 19). If you are using pre-finished metal or vinyl soffit, then the ridge board does not need to be notched. FRMG 202/222 Roof Framing LO1 Page 20

27 Figure 19: Notching Ridge Board at Ends Ridge Board Supports When the roof slope is less than 1 in 3 (less than 4 12 ), the ridge must be supported. There are two ways to support the ridge mentioned in the NBC. They are as follows: 1. by a load bearing wall under the ridge and resting on suitable support underneath, or 2. by using a "ridge beam" sitting on supports. The ridge beam should be not less than a single or 2 6. The beam is to be supported every 1200 mm or 4'-0", by a vertical 2 4 (see the following figure). Figure 20: Ridge Support FRMG 202/222 Roof Framing LO1 Page 21

28 Common Rafter After the line lengths of the common rafter and rafter tail have been established, the next step is to lay out the plumb and level lines and make the necessary deductions. 1. Plumb Cuts To lay out a plumb cut on a rafter, position the rafter with the crown edge away from you, as in Figure 21. Position the framing square as shown in Figure 21. Note how the rafter represents the hypotenuse of a right angle triangle. Figure 21: Laying Out a Plumb Cut on a Common Rafter If you are using a 4 12 slope, place the 4" marking (on the tongue) and the 12" marking (on the body) on the near side of the rafter (see Figure 21). Mark along the tongue. This is a plumb cut. 2. Level Cuts (Seat Cuts) Mark along the body for a level cut. (A level cut is sometimes called a SEAT cut). See Figure Birdsmouth To lay out a birdsmouth first draw a plumb line at the required location. Before the level cut or seat cut can be drawn, the depth of the birdsmouth must be decided. The NBC calls for a minimum of 38 mm (1½) end bearing for a rafter. That means the level cut must be at least 1½ inches long. Other considerations are a. the seat cut should not be longer than the width of wall plates (if possible), and b. do not weaken the rafter with a too deep birdsmouth (see Figure 22). The maximum depth of the birdsmouth should be no more than one-third the depth of the rafter stock measured along the plumb line (see Figure 22). This is called the "one-third two thirds" rule. FRMG 202/222 Roof Framing LO1 Page 22

29 Figure 22: Layout of a Common Rafter For example when using a 4 12 slope, if you measure the plumb line, it measures about 3⅝ inches or 3.625". One third of 3.625" is 1.21" or ". Deductions on the Common Rafter Layout A deduction is a shortening of rafter so another member can fit into the roof. If a ridge board is used, the common rafter must be shortened at the top to make room for the ridge board. A deduction is required on the rafter tail for a rough fascia board. The theory length of the common rafter is to the centre of the ridge board and to the outside of the rough fascia. The amount of deduction depends upon the thickness of the ridge board. The deduction is always one-half the thickness of the ridge board. For example if the ridge board is a 2 6 which is 1½ inches thick, one-half its thickness is ¾ inch. This deduction must be taken off at right angles to the plumb line on the side of the rafter (not on top of the rafter) (see Figure 23). The amount of the deduction for the rough fascia thickness of the rough fascia (usually 1½ inches thick). The deduction is always the full thickness of the fascia. This deduction is again taken off of the side of the rafter, not on top (see Figure 23). Figure 23: Deductions for Ridge Board and Rough Fascia FRMG 202/222 Roof Framing LO1 Page 23

30 3.3 Review Exercise 1. If a building is 24'-0" 40'-0" with a 2'-0" overhang all around, what is the theory length of the ridge board? 2. What determines the minimum width of the ridge board? 3. What figures should be used on the Stanley steel square to lay out the plumb cut of a common rafter for a 1:3 slope? and, mark on 4. The "set point" on the Stanley steel square for common rafters is inches. 5. What figures should be used on the Stanley steel square to lay out the seat cut of a common rafter for a 1:1.33 slope? and, mark on 6. What are three factors to consider when determining the depth of the birdsmouth? 7. The amount to deduct at the plumb cut of a common rafter for a 2 6 ridge board is. 8. The amount to deduct at the top of a common rafter for a 2 6 ridge board is measured a. along the top of the rafter. b. along the theory line. c. at right angles to the plumb cut. 9. The amount to deduct at the tail plumb cut of a common rafter for a 2 6 fascia is. FRMG 202/222 Roof Framing LO1 Page 24

31 10. The amount to deduct at the tail plumb cut of a common rafter for a 2 6 fascia is measured a. along the top of the rafter. b. along the theory line. c. at right angles to the plumb cut. 11. The first common rafter laid out and cut becomes the for the rest of the rafters for a similar slope and span. 3.4 Instruction Sheet Layout a Common Rafter Resources Required 1. building size 24'-0" 40'-0" 2. roof slope overhang 16 inches 4. ridge and rough fascia framing square 6. pocket tape and pencil 7. pair of stair gauges (optional) 8. 16'-0" pair of sawhorses 10. calculator Directions 1. Lay out the common rafter for the above building. Do not cut it out. Procedure Steps 1. Calculate the line length. of rafter of rafter tail Key Points 2. Lay 2 4 on sawhorses. crown edge away from you 3. Lay out top plumb line at ridge. see Figure 24 set square to slope and attach stair gauges, if available Figure 24: Laying Out Plumb Cut at Ridge FRMG 202/222 Roof Framing LO1 Page 25

32 Steps Key Points 4. Square across top of rafter. on crown edge line up with top of plumb line see Figure 25 Steps Figure 25: Square Across Top of Rafter Key Points 5. Measure line length of rafter. along top of rafter from squared line at top plumb line theory line length is centred on rafter see Figures 25 and Square top of rafter at birdsmouth. see Figure Draw plumb line at birdsmouth. line up with squared line on top see Figure 26 Figure 26: Theory Length of Rafter (Line Length) FRMG 202/222 Roof Framing LO1 Page 26

33 Steps Key Points 8. Measure line length of rafter tail. along top of rafter measure from plumb line at birdsmouth see Figure 27 square across top of rafter Steps Figure 27: Laying Out Rafter Tail 9. Draw plumb at fascia. see Figure 27 Key Points 10. Measure and draw seat cut at birdsmouth. use the one-third, two-thirds rule see Figure 28 seat cut minimum of 38 mm (1½") Figure 28: Birdsmouth Layout FRMG 202/222 Roof Framing LO1 Page 27

34 Steps Key Points 11. Lay out ridge board deduction. deduction will be one-half the thickness of the 2 6 ridge measure deduction on side of rafter, not on top measure deduction at 90 degrees to plumb line draw plumb line mark this as "cut line," or cross-cut original plumb line see Figure 29 Figure 29: Laying Out Ridge Board Deduction Steps 12. Lay out for rough fascia on rafter tail. Key Points deduction will be the full thickness of 2 6 rough fascia make deduction on side of rafter measure at 90 degrees to plumb line draw new plumb line (cut line) see Figure 30 Figure 30: Deduction for Rough Fascia Steps 13. Have your instructor check your work. Key Points put your name on the rafter tail FRMG 202/222 Roof Framing LO1 Page 28

35 Criteria: All items must be checked yes for attainment. 1. The crown is up. 2. Plumb lines are at 4 and 12 angle. 3. Rafter squared across top. 4. Line length of common rafter is correct length. 5. Line length of rafter tail is correct length. 6. Birdsmouth correct size and correct angles. 7. Proper deduction made at top for ridge. 8. Proper deduction made for rough fascia. 9. All cut lines are clearly distinguishable. Yes No No 3.5 Practical Exercise Laying Out a Common Rafter Using the Stepping Out Method Resources Required 1. building size 24'-0" 40'-0" 2. roof slope overhang 2'-0" 4. ridge and rough fascia '-0" pair of sawhorses 7. faming square 8. pencil 9. stair gauges Directions 1. Lay out the common rafter for the above building. Do not cut it out. Procedure Steps Key Points 1. Determine the number of steps required. span 2 = total run of rafter 24'-0" 2 = 12'-0" therefore there are 12 units of runs also 12 steps to layout FRMG 202/222 Roof Framing LO1 Page 29

36 Steps Key Points 2. Place 2 4 on saw horses. 3. Lay out top plumb cut. using 4 and 12 on square 4. Lay out and mark step 1. using 4 and 12 on your square set stair gauges on square to slope see Figure 31 Figure 31: Lay Out the Top Plumb Cut and the First Step Steps Key Points 5. Lay out step 2. slide square down line up 4 inch mark on square with mark on rafter from first step see Figure 32 Steps Figure 32: Laying Out the Second Step 6. Lay out remaining steps. 12 steps needed see Figure 33 Key Points Figure 33: Lay Out 12 Steps FRMG 202/222 Roof Framing LO1 Page 30

37 Steps 7. Draw plumb line at birdsmouth. at end of 12th step see Figure 34 Key Points Steps Figure 34: Laying Out Birdsmouth Key Points 8. Step out rafter tail. 2 full steps (overhang 2'-0") 9. Draw plumb line at end of rafter tail. 4 and 12 on framing square 10. Measure depth of birdsmouth and draw seat cut. use ⅓ - ⅔ rule 11. Deduct for ridge board at top. half the thickness of 2 6 ridge board measure deduction on side of rafter draw new plumb line (cut line) 12. Deduct for rough fascia at bottom. full thickness of 2 6 rough fascia measure deduction on side of rafter draw new plumb line (cut line) 13. Have your instructor check your layout. put your name on the rafter tail Note: The stepping out method isn't as accurate as measuring the line length of a rafter. The square can slip during each step causing an error. It is also slower. FRMG 202/222 Roof Framing LO1 Page 31

38 Criteria: All items must be checked yes for attainment. 1. The crown is up. 2. Plumb lines are at 4 and 12 angle. 3. All 12 steps laid out accurately and marked. 4. Two steps for rafter tail laid out and marked. 5. Birdsmouth laid out accurately. 6. Deductions at top for ridge correct. 7. Deductions for rough fascia correct. 8. All cut lines are clearly distinguishable. Yes No Learning Step 4 Determine Rafter Sizes and Support Systems for Gable Roofs 4.1 Instruction Sheet Common Rafter Size and Support Size of Common Rafters The distance a common rafter will safely span depends on several factors. The factors are as follows: 1. species of wood, 2. grade of wood, 3. size of stock, 4. spacing of rafters, and 5. snow load on roof. Figure 35: Sample Roof FRMG 202/222 Roof Framing LO1 Page 32

39 Rafter Spans To decide on the size of stock to be used for rafters for a specific building, first calculate the span of the rafter. As an example we'll use a building width of 28 feet. The common rafter spans only one-half this distance, or 14 feet. Next, decide on the species and grade of lumber to be used for the rafters. For our example we will use Hem-Fir No. 2 grade material. Check the blueprints for the rafter spacing. We will use 24 inches. Now, we can use rafter tables from the National Building Code of Canada to determine the size of the rafter stock to be used. The rafter tables in the National Building Code of Canada, (Tables A-6 and A-7), give the spans for various sizes, species, and grade of lumber under a variety of spacings and snow loads. Don't use the tables on roof joists (A-4 and A-5). In the National Building Code of Canada turn to Table C-2 in Appendix C and check out Saskatchewan towns and cities. Look under Ground Snow Load, S S (S R is rain load). You will notice that southern cities such as Moose Jaw and Regina have a ground snow load of 1.4 kpa. Cities in central Saskatchewan such as Prince Albert have a heavier snow load of 1.9 kpa. The snow loads shown in the rafter tables are 1.0, 1.5, 2.0, 2.5, and 3.0. For example, Moose Jaw's snow load is 1.4 kpa, so go to the next largest in the rafter in the rafter tables, which would be 1.5. To use the rafter tables, find the table with the required snow load. In our example house, Regina snow load is 1.4 kpa, so use 1.5 kpa in the rafter table. Next, find the species of lumber to be used under the heading Commercial Designation, (Hem- Fir), and the grade of the lumber (No. 2). Now look in the 1.5 kpa column for the rafter spacing. We are using a 24 inch O.C. rafter spacing, which is very close to 600 mm O.C., so look under 600 spacing. Follow that column down until you find a span that is equal to or slightly greater than the required span. The tables are in metric, so we have to convert our 14'-0" rafter span to mm (14'-0" = mm) to find a number in the tables that is equal to or greater than 4268 mm. You'll find we need a mm (2 8) rafter. A 2 6 will only span 3500 mm. Intermediate Roof Supports An intermediate support is often used on roofs to reduce the span of the rafters, allowing a smaller size of framing material to be used. Intermediate supports can be provided by using dwarf walls, struts, or collar ties. These supports are placed in the middle-third of the rafter line length (see Figures 37 and 38). When an intermediate support is used, the span of the rafter is reduced. In Figure 37 the rafter spans 12'-0" without an intermediate support. When a support is used, the span of the rafter is reduced to 6'-0". FRMG 202/222 Roof Framing LO1 Page 33

40 Dwarf Walls Dwarf walls are framed in the same manner as a load bearing wall and must be adequately supported by ceiling joists and/or bearing walls. The top plate is installed on an angle so the rafter has full bearing on the top plate. Studs must line up with the rafters, or a double top plate has to be used. Figure 36: Dwarf Walls Figure 37: Location of Intermediate Supports FRMG 202/222 Roof Framing LO1 Page 34

41 Struts Struts are made from not less than 2 4 material and are placed under each rafter (see Figure 38). The struts rest on the ceiling joists. The struts are usually installed on an angle of at least 45 to the horizontal. Collar Ties A collar tie is a horizontal member usually cut from a 2 4 and is used to connect two opposite rafters (see Figure 38). Unlike dwarf walls or struts, collar ties do not transfer the loads on the roof to the ceiling framing. Instead, collar ties transfer the load to the rafter on the opposite side of the roof, so in effect two rafters will be carrying the imposed load. In most cases, the length of the collar tie will be the same as the run of the common rafter (onehalf the building width). However, the length may change because the collar tie is not placed at the mid-point of the rafter length. This might happen because more height under the collar tie is wanted, for more usable attic space, or because positioning the collar tie higher or lower will permit the use of a more convenient length of material. As long as the collar tie is attached to the rafter somewhere in the middle third of the length of the rafter, it will be acceptable. Figure 38: Struts and Collar Ties FRMG 202/222 Roof Framing LO1 Page 35

42 Laying Out and Cutting Collar Ties 1. Calculate the theory length of the collar tie. 2. Take the collar tie material (usually a 2 4) and draw a centre line on one face (see Figure 39). Figure 39: Laying Out a Collar Tie 3. Measure out the line length of the collar tie along the scribed centre line (see Figure 39). 4. Lay out angled cuts at both ends. use same figures on square as for common rafter (e.g ) set the figure on the square onto the scribed line (see Figure 40) draw a line along the body Figure 40: Laying Out Angled Cut reverse the square and lay out the angle at the others end of the collar tie When nailing collar ties in place, keep the ends of collar ties down ¼ inch or so, so if the rafters shrink, there won't be bulges in the roof sheathing at every collar tie. FRMG 202/222 Roof Framing LO1 Page 36

43 Ridge Support The common rafters on a gable roof impose an outward force on the exterior walls of the building, causing the walls to bulge. To avoid this problem, the ridge needs to be supported. There are three main methods of providing support to the ridge: 1. Load Bearing Walls A wall can be constructed under the ridge and over suitable bearing to carry the load of the ridge. This wall would transfer the load to the foundation of the building. 2. Ridge Beams A can be used in place of a ridge board and provide the required ridge support if it is supported every 1200 mm by vertical members extending to suitable bearing, such as a load bearing wall down below. A built-up wood beam conforming to Table A-12 of the National Building Code of Canada may also be used. 3. Ties Across the Roof Ceiling joists act as ties to prevent the walls from pushing outwards, which in turn prevents the ridge from sagging. Ceiling joists require extra nailing to do this. Some buildings use metal rods in place of the ceiling joists. 4.2 Instruction Sheet Frame an Opening in a Roof Sometimes an opening must be framed into a roof, for such things as a brick fireplace chimney, skylight, etc. Roof openings, like floor openings, are framed using headers and trimmers (see Figures 41 and 42). Double headers are used at right angles to the rafters. Notice how the headers are stepped on top to follow the roof slope. The rafters are doubled on each side of the opening. The National Building Code calls for a 2 inch (50 mm) clearance between the framing and the chimney. Figure 41: Framing a Roof Opening FRMG 202/222 Roof Framing LO1 Page 37

44 To calculate the distance between the upper and lower headers, along the rafter, calculate as follows: Example: Chimney in Figure 41-4'-0" by 2'-0" Roof Slope inch clearance all around Horizontal measurement of chimney plus clearances 4'-0" + 2" + 2" = 4'-4" 4'-4" = 4.33 units of run Unit-of-line length for common rafter at 4 12 slope is 12.65" Length of chimney opening = 4.33 units of run 12.65" (along rafter) = inches = 4'-6 ¾" The length of the short rafters above and below the opening can be calculated mathematically (see Figure 42). Figure 42: Framing a Roof Opening In Figure 42, the short rafter above the opening has a run of 6'-8" or 6.67 units of run. L.L. = " = 84.38" = 7'-0 ⅜ " minus deductions FRMG 202/222 Roof Framing LO1 Page 38

45 Lay out the rafter on the rafter stock as you did the common rafter. Deduct the following: one-half thickness of ridge at top (¾") two thickness of headers at bottom (3") Remember these deductions must be made on the side of the rafter, at 90 degrees to the plumb lines. You cannot subtract 3¾" from the line length of 7"-0⅜". In Figure 42, the short rafter below the opening has a run of 3'-0" or 3 units of run. L.L. = " = 37.95" = 3' " Lay out the rafter on rafter stock and at the top. Deduct the following: two thicknesses of header material The rafter tail is done the same as for the common rafter. Roof Cricket or Saddle Water and ice will build up behind a wide chimney. To prevent this, a small roof is built behind the chimney, on top of the roof sheathing. This small roof is a cricket or saddle (see Figure 41). Construction of this saddle will be covered in Level 4 course manual on intersecting roofs. 4.3 Reading Assignment From the National Building Code of Canada, study the following: nailing for framing roof and ceiling framing rafter to joist nailing 4.4 Review Exercise 1. How does an intermediate support affect the span of a rafter? 2. Name three ways of providing intermediate support for rafters. FRMG 202/222 Roof Framing LO1 Page 39

46 3. Where, under the span of the rafters, should the intermediate supports be placed? 4. What must be done to ceiling joists if they support an intermediate support, such as a dwarf wall? 5. How wide and thick must a ridge beam be? 6. When must the ridge be supported in a roof? 7. Name two ways of supporting a ridge. 8. If collar ties are more than 8'-0", what is needed? 9. Complete the following: a. Rafter to the rafter plate. b. End of collar tie to the rafter. c. Strut to the rafter. d. Rafter to the ridge board (end nailed). e. Rafter to joist with ridge supported. Minimum Number of Nails Minimum Size of Nails FRMG 202/222 Roof Framing LO1 Page 40

47 f. Rafter to the joist with ridge unsupported, building width 8.2 m, roof snow load 1.5 kpa, roof slope 1 in 2, rafter spacing 600 mm. g. Each rafter to joist with ridge unsupported, building width 7.5 m, roof snow load 1.5 kpa, roof slope in 1 in 3.33, rafter spacing 400 mm. Minimum Number of Nails Minimum Size of Nails Select the most appropriate response to the following statement(s) and/or question(s). 10. When used to support rafters, struts must be placed to the ceiling joists. a. at right angles b. at 45 degrees c. perpendicular 11. When dwarf walls are used to provide intermediate support for the rafters, they are placed to the ceiling joists. a. at right angles b. at 45 degrees c. parallel 12. Give the maximum allowable spans for the following rafter stock. Size Species Grade Spacing Snow Load Max. Span Spruce #1 600 mm Hem-Fir #2 400 mm Spruce #1 400 mm Hem-Fir #3 600 mm Spruce #2 300 mm Douglas Fir #1 400 mm If a dwarf wall, not directly above a suitable bearing, is used to provide intermediate support for rafters, the ceiling joists must be increased by at least inch(es) in depth to support the roof load. 14. The seat cut of a rafter must be a minimum of mm in length. 15. If a roof opening is greater than rafter spaces, the rafters must be doubled on each side of the opening. 16. If the ridge board is 17.5 mm thick, rafters may be offset an amount equal to. FRMG 202/222 Roof Framing LO1 Page 41

48 Learning Step 5 Lay Out and Construct Gable End Studs, Gable Ends, and Gable Roof Ladders 5.1 Reading Assignment Study the following: from the textbook, Carpentry, study "Gable End Studs" from the textbook, Canadian Wood-Frame House Construction, study "Gable End Framing and Projections" 5.2 Instruction Sheet Common Rafter Size and Support After the gable roof has been framed, the next step is to frame in the gable end studs. Just as with the common rafter, the calculations are based on the right angle triangle. Gable End Geometry The line length of a gable stud is the theory length, perpendicular from the top of the wall plates to the intersecting point of the theory line of the common rafter. Figure 43: Gable Stud Geometry The run of the gable stud is the distance from the theory line of the stud centre line to the corner of the building. The line length of the stud corresponds to the altitude of a right angle triangle formed by the run line, the rafter theory line, and the stud theory line. FRMG 202/222 Roof Framing LO1 Page 42

49 Figure 44 Theory Length of Gable Studs Two methods of determining the theory length of gable studs are as follows: Formula: Theory of Length of Gable Studs = Run of Gable Stud Unit of Rise Formula: Theory of Length of Gable Studs = Slope Run of Stud Example: A gable stud placed 4'-0" from the corner of the building with a roof slope 5 12 (refer to Figure 43). Run of Gable Stud Unit Rise Number of units of run (run of stud in feet) = 4 Unit of rise = 5" Theory length = 4 5 inches The theory length of the gable stud is 20 inches or 1'-8". FRMG 202/222 Roof Framing LO1 Page 43

50 Slope Run of Stud Slope = 5 12 Run = 4 feet ' 1.66' 1' 8" Figure 45 Difference in Length for Gable End Studs After the length of one stud (usually the longest) is calculated, the length of the rest of the studs in the roof pattern are usually determined by subtracting a common difference in length. This amount is determined by the following method: Formula: Unit of Rise Common Difference of Gable Studs=O.C.Spacing of Studs Unit of Run Example: studs at 16 inches on centre slope 5 12 Common Difference = 16" 5 12 = = 6.66" or inches The common difference between successive studs is 6.66". This amount is subtracted from the longest stud for the second longest one, and so on until the shortest stud is reached. FRMG 202/222 Roof Framing LO1 Page 44

51 Actual Length of Gable End Studs The actual length of gable end studs is the plumb measurement from the underside of the rafter to the theory line of the rafter (the depth of the cut at the birdsmouth) subtracted from the theory length of the gable stud. Orientation of Gable End Studs Figure 46: Actual Length - Theory Length Minus "A" In certain circumstances (National Building Code of Canada, ) studs may be framed on the flat. This permits gable end studs to be placed in this manner. Gable Studs Placed on the Flat (No Top Plate) This is the simplest method of framing gable studs. One cut at the slope of the roof is all that is required. However, the top and bottom ends must be toe-nailed to the plate and rafter. Gable Studs Placed on Edge (No Top Plate) Figure 47: Studs on the Flat These studs are more complicated and difficult to cut. Study the following procedure carefully and apply this knowledge when you perform the performance test at the end of this learning outcome. FRMG 202/222 Roof Framing LO1 Page 45

52 Steps 1. Calculate the length. as previously explained Key Points 2. Lay out the theory length. on the edge of the gable stud stock on the centre-line see "A" in Figure Deduct for the common rafter. along the centre line, an amount equal to the depth of the birdsmouth see "B" in Figure Draw the first angle cut. through the centre-line at point of deduction slope same as the plumb cut of the rafter see "C" in Figure Add the width of the rafter. from point "C" in Figure 48 along centre-line the width of the rafter along the plumb cut, less 1 4 " see "D" in Figure 48 Steps Figure Draw the second angle cut. as in step 4 Key Points 7. Square both lines. on the sides of the stud, top and bottom, on both sides as in Figure 49 "E" and "F" FRMG 202/222 Roof Framing LO1 Page 46

53 Steps Key Points 8. Mark the depth of cut. thickness of the rafter from the face side of the stud (outside) see "G" in Figure Mark the plumb cut. from the bottom cut to the top cut parallel to the edge of the stud see "H" in Figure 49 Figure 49 Both of these types of gable ends are used only for roof overhangs less than 16 inches. For overhangs 16 inches or more, lookouts are required. The gable studs will have a top plate supporting the lookouts (see Figures 51 and 52). 5.3 Instruction Sheet Lay Out a Gable End and Roof Ladder In order to speed up the roof construction and avoid the use of scaffolds, gable ends and roof ladders are either delivered to the job sites, prefabricated and ready for installation with roof trusses, or they are prefabricated on the jobsite. Figure 50 FRMG 202/222 Roof Framing LO1 Page 47

54 Gable End Top Plates When framing a gable roof there are several methods of framing the gable ends and roof overhang. A common method is to omit the first common rafter at the edge of the building at the gable end and build a sloping wall at the end of the building (see Figure 51). Figure 51 The gable end is framed up with a sloping top plate. The easiest way to obtain the length of their top plate is by measuring the underside of the common rafter, from the start of the birdsmouth to the top of the rafter, along the bottom of the rafter (see Figure 52). Figure 52: Measuring Length of Top Plate The theory length of the gable stud is the height from the bottom plate to the theory line of the common rafter (the line that passes through the birdsmouth). To get the actual length of the gable stud, two deductions must be made at the top. The thickness of the top plate, which because it is running at an angle, will be more than 1 ½ inches. (To get this thickness, draw a slope angle on the edge of a piece of 2 x 4 and measure it with your tape.) (see Figure 53). FRMG 202/222 Roof Framing LO1 Page 48

55 The second deduction is the vertical height depth of the birdsmouth. Measure this distance on a common rafter (see Figure 53). Figure 53: Deductions on Gable End Studs Remember this height is through the centre of the stud, not the edge. Lookouts and Barge Rafters To support the roof overhang on the gable ends, 2 4 lookouts are used (see Figure 50). A lookout is a short member at right angles to the main rafter, and set on top of the gable end wall. A barge rafter which is a common rafter without a birdsmouth, is nailed to the lookouts. If metal fascia and soffits are to be used, the barge rafter will be a 2 6. The lookouts are usually 2 4 and are spaced at the same spacings as the common rafters. Layout of the lookouts starts at the bottom, on the outside of the rough fascia (see Figure 54). Figure 54: Spacing of Lookouts FRMG 202/222 Roof Framing LO1 Page 49

56 The length of the lookouts depends on the roof overhang. Remember to deduct the thicknesses of the barge rafter (rough fascia) from the overhang distance (see Figure 55). Figure 55: Lookouts and Barge Rafters The lookouts and barge rafters can be assembled in a complete unit and then lifted up into place. These units are called ladders. Roof Overhangs Less than 16 inches Gable ends with roof projections less than 16 inches don't need lookouts for support. A common rafter is placed on top of the gable end and the overhang is made up on the ground and lifted into place (see Figure 56). Figure 56: Overhangs Less Than 16 Inches FRMG 202/222 Roof Framing LO1 Page 50

57 5.4 Review Exercise 1. Using Method A, determine the theory length of the following gable studs. Check your answer using Method B. Slope Run Line Length of Gable Stud 1:2.4 4'-0" 1:2 12'-0" 1:1.71 7'-6" 1: '-6" 1:3 14'-0" 1:4 9'-0" 1:1.5 10'-6" Note: Method A - number of units of run unit rise Method B - slope run Method A Method B 2. Fill in the spaces to indicate the difference in length for the following gable end studs. Slope O.C. Spacings Difference in Length Gable 1:2.4 16" 1:2 24" 1: " 1:1.3 16" 1:3 24" 1:4 12" 1:1.5 16" FRMG 202/222 Roof Framing LO1 Page 51

58 3. Calculate the theory length of the gable studs in the following roof (see Figure 57). The building is 12'-0" wide, the studs are spaced 16 inches O.C. The layout is from the centre of the building to the sides, but offset from the centre 8 inches each way. The roof slope is 1:2.4. Figure 57 a. longest stud b. 2 nd longest stud c. 3 rd longest stud d. shortest stud Line Length of Gable Stud 4. When framing a gable end, how is the length of the top plate calculated? 5. Calculate the theory length of the longest gable end stud for the following building: Building 24'-0" 30'-0" Roof Slope 4 12 Gable Studs 24 inches O.C. Layout of studs start at corner of building 6. Calculate the theory length of the second longest gable stud for the following building: Building 18'-0" 24'-0" Roof Slope 5 12 Gable Studs 16 inches O.C. Layout of studs start at centre of building FRMG 202/222 Roof Framing LO1 Page 52

59 7. State the formula for finding the common difference of gable studs. 8. Using the above formula, calculate the common difference of gable studs. a. Question 5: b. Question 6: 9. What does a roof ladder consist of? 10. When laying out gable studs, when using a top plate, what are the deductions that must be made from the theory length, for the stud to fit? 11. Where does the spacing of lookouts start? 12. What figures are used on the framing square to layout the top cut on a gable stud? a. Question 5: and and mark along the. b. Question 6: and and mark along the. 13. When marking out the top plate for a gable end, what figures are used on the framing square for the bottom angle? a. Question 5: and and mark along the. b. Question 6: and and mark along the. FRMG 202/222 Roof Framing LO1 Page 53

60 FRMG 202/222 Roof Framing LO1 Page 54

61 Performance Test 1 Construct a Gable Roof Name: Student ID: Date: Given framing stock for ridge, rough fascia, and rake rafters 3. portable electric handsaws 4. STK 5. ladders, 8'-0" step ladders 6. saw horses 7. three inch common nails Directions 1. The performance test will be constructed on top of the walls framed up in FRMG Wall Framing. The ceiling joists must be in place and the rafter plates installed on top of the joists. 2. Each student will construct one-quarter of the roof on this building. Your instructor will assign you a corner of the roof to build. Steps 1. Check rafter plates for correct measurements. Key Points make sure width of plates is 12'-0" from outside to outside of plates 2. Lay out rafter centres on rafter plate. start layout from outside of building and works towards the centre rafters at 16 inch on centre no rafter on outside of building, this is where the gable end will be built 3. Count the number of common rafters you will need. remember to deduct 1 rafter for the chimney opening use single rafters on each side of the opening FRMG 202/222 Roof Framing LO1 Page 55

62 Steps 4. Calculate the line length of rafters and rafter tail. Figure 58: Roof Framing Project Four Students Key Points roof slope given in Figure ridge and rough fascia 2 6 barge rafter 5. Lay out and cut common rafters. birdsmouth depth, use rule 6. Calculate length of ridge. for one-half the building plus overhang at one end do this with your partner on other side of building. You will both frame to the same ridge deduct for 2 6 barge rafter 7. Cut ridge. cut ridge ½ inch short so that the two ridges don't touch in the centre of the building 8. Lay out rafter centres on ridge. before nailing in place on both sides FRMG 202/222 Roof Framing LO1 Page 56

63 Steps 9. Working with your partner, install two common rafters on each side and then the ridge board. Key Points nail as per NBC use 3 inch common nails in shop Caution! Do not nail through the top of the rafter into the ridge. These nail heads may damage saw blades if roof sheathing requires trimming. Toe-nail or end nail only. Note: When starting to put up the commons and the ridge, nail the commons at the birdsmouth and let then rafters lean against each other at the top. When you have four rafters nailed like this (two on each side of ridge) then put the ridge in place by spreading the rafters apart and sliding the ridge into position. Steps Key Points 1. Install remaining common rafters. leave space for opening in roof 2. Calculate and cut headers. for roof opening 3. Mark location of headers. on sides of common rafters calculate distance mathematically 4. Install outside header at each end of opening. 5. Calculate and cut short rafter above and below opening. don't double headers until short rafters are nailed in place nail in place check alignment with straight-edge (lay straight edge on top of both short rafters and over opening and check alignment with tops of headers) 6. Double up headers. step headers to keep them flush with commons use 3 inch common nails in shop 7. Calculate, cut, and install two short rafters inside opening. to make opening proper width check opening for square 8. Measure length of top plate for gable end. measure underside of common rafter from start of birdsmouth to ridge see Figure Lay out angles for top plate. plumb cut at top seat cut at bottom use roof slope numbers, same as for common rafter 10. Cut top plate. after cutting, place top plate under a common rafter and see if it fits see Figure 59 FRMG 202/222 Roof Framing LO1 Page 57

64 Steps Figure 59: Spacing of Gable End Studs Key Points 11. Nail top plate into position. on gable end keep plate down from top of ridge same distance as underside of common rafter 12. Mark out location of gable end studs. on bottom wall or rafter plate see Figure 59 first stud centred under ridge remaining studs at 16" O.C. 13. Cut and install centre gable end stud. measure the height with tape fits under ridge board check ridge for level before measuring and cutting stud work with partner on this gable end stud 14. Calculate theory length of second longest gable. FRMG 202/222 Roof Framing LO1 Page 58 studs on 16 inch centres 15. Calculate deductions at top of studs. depth of birdsmouth top plate (on an angle) 16. Lay out, cut, and install second stud. check for plumb don't force plate upwards check top plate for straightness 17. Calculate common difference of gable studs. as previously discussed 18. Lay out, cut, and install remaining studs. check for plumb check top plate for straight 19. Cut and install lookouts. 16 inches on centre

65 Steps 20. Cut and install barge rafter. 2 6 stock 21. Cut and install rough fascia. 2 6 stock on all rafter tails 22. Calculate, lay out, cut, and install once collar tie. as per NBC 2 4 stock Key Points 23. Brace the roof to keep gable end plumb. brace down to top of partition 24. Have your instructor check your work. 25. When you dismantle your roof save the common rafters. Tolerances: All cuts and fits must be ± 1 16 inch. for the hip roof you will do next Criteria: All items must be checked yes for attainment. 1. Rafters are on 16 inch centres. 2. Line length of common rafters was correct. 3. Length of ridge board is correct. 4. Birdsmouth is correct size and shape. 5. Common rafters are nailed according to NBC. 6. Alignment of rafter tails are correct. 7. Alignment of top edge of rafters is good. 8. Overhang is correct width. 9. Fascia is at correct height on rafter tails. 10. Fascia is straight. 11. Gable end studs are on correct centres. 12. Gable end studs are plumb. 13. Gable end studs did not bow top plate. 14. Top plate on gable end correct length, angles good. 15. Lookouts are correct length. 16. Lookouts are properly nailed, aligned with commons. 17. Lookout spacing at 16 inches from fascia, are correct. 18. Barge rafter is cut and installed correctly. Yes No Mark FRMG 202/222 Roof Framing LO1 Page 59

66 19. Roof opening is in correct location. 20. Roof opening is correct length and width. 21. Roof opening headers are in alignment with rafters. 22. Short rafters at opening are cut correctly. 23. Short rafters are in alignment with headers. 24. Collar tie is correct length and correct angles. 25. Collar tie is properly nailed, in correct location. 26. Work site was kept tidy and safe. 27. Worked cooperatively with partner. Mark Yes No Mark Comments: FRMG 202/222 Roof Framing LO1 Page 60

67 Learning Step 6 Calculate and Lay Out a Shed Roof Rafter 6.1 Reading Assignment From the textbook, Carpentry, study the chapter, "Shed Roofs, Dormers, and Other Roof Framing." 6.2 Instruction Sheet Calculate and Lay Out a Shed Roof Rafter A shed roof is one-half of a gable roof and the rafters for a shed roof are similar to a gable roof, except they have two birdsmouths and two overhangs (see Figure 60). Figure 60: Example of a Shed Roof Calculating the Theory Length of a Shed Rafter The run of a shed rafter is equal to the width of the building minus the thickness of one wall (see Figure 61). To calculate the line length of a shed rafter, multiply the number of units of run the unit-of-line length from the framing square tables. Figure 61: Lay Out of a Shed Rafter FRMG 202/222 Roof Framing LO1 Page 61

68 1. Find the unit line length Find run. 10'-0"- 4"= 9'-8" = Find the length from plumb line to plumb line = " = 9' " 4. Find the rafter tail lower. 1 unit of run = 12.37" = 1'-0⅜ 5. Find the rafter tail upper. 12" + 4" = 16" 12 = 1.33 units of run = = 1' Layout of a Shed Rafter 1. Draw a 3 12 plumb line on the face at the top end of the rafter. 2. Measure down on the rafter back 16½" (tail O.H. + wall thickness). 3. Draw a plumb line and seat cut for the birdsmouth. 4. Measure down the rafter back to the bottom birdsmouth (9' "). 5. Draw a 3 12 plumb line. Lay out the lower birdsmouth the same depth as upper birdsmouth. FRMG 202/222 Roof Framing LO1 Page 62

69 Calculate the Theory Line Length of a Shed Rafter When the Roof Slope Isn't Given In Figure 63 a sample shed roof is shown with the higher wall 12 inches higher than the shorter wall. The width of the shed is 8 feet. The rafter tails above the lower wall are similar to a common rafter. If a fascia is used, deduct it's thickness on the side of the rafter. Its line length will be measured on the back from the birdsmouth plumb line. When laying out the upper overhang, the line length must be the overhang plus the wall thickness and also measured on the back from the plumb line of the upper birdsmouth. Figure 62: Shed Roof Rafter Use square root to calculate the line length of the rafter. The roof rises 12 inches and the shed is 8 feet wide. The wall thickness is 4". Run = 8'-0" - 7'-8" = 7.67' a b ' 7'8 or " Line length without overhangs and 1 wall thickness. The number on the square that would be used for a plumb cut or a seat cut would be 1 and 8 because the building is 8 feet wide and the roof rises 1 foot. FRMG 202/222 Roof Framing LO1 Page 63

70 The roof slope can be calculated using the following ratio: 1 x x 12 x x :12 The roof slope is 1.56 : For layout it is necessary to round to the nearest inch,so round to To calculate the line length of the overhangs, first we need the unit of line length for a 1.5:12 slope. 1.5 slope isn't given on the framing square, so use square root to calculate it. C C C 12.09" Unit Line Length The overhang is 16 inches or 1.33 units of run. The theory length then would be calculated (units of run) inches = inches = 1' " 6.3 Review Exercise 1. Calculate the following theory line lengths building 12 feet wide roof slope 4 12 overhang 12 inches 5½" exterior wall ½ sheathing a. line length of shed rafters FRMG 202/222 Roof Framing LO1 Page 64

71 b. line length of overhang 2. Describe how the upper birdsmouth on a shed rafter is laid out. FRMG 202/222 Roof Framing LO1 Page 65

72 FRMG 202/222 Roof Framing LO1 Page 66

73 Performance Test 2 Lay Out a Common Rafter, Gable End Stud, Ridge Board, and Collar Tie Name: Student ID: Date: Given 1. 16'-0" - 2 4's 2. framing square 3. tape measure Directions 1. At the end of this roof framing course, you will be required to lay out a a. common rafter, b. ridge, c. gable end stud, and d. collar tie for a given building. 2. Your instructor will give you the necessary information and checklist when you start the test. Criteria: All items must be checked yes for attainment. 1. The performance test will be available from the instructor when you are prepared to complete it. FRMG 202/222 Roof Framing LO1 Page 67

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75 Learning Outcome 2 Construct Conventional Hip Roofs Learning Step 1 Calculate and Lay Out the Ridge Board and Hip Rafters 1.1 Reading Assignment From the textbook, Carpentry, read the chapter "Hip Roofs." 1.2 Instruction Sheet Ridge Board for Hip Roofs The ridge board for a hip roof is shorter than a ridge for a gable roof because the hip roof slopes in four directions, instead of two for a gable roof. Theory Length The theory length of a ridge for a hip roof is as follows: Formula: Ridge for Hip Roof = Length of Bldg - Width of Bldg (Theory Length) Example: If we have a building that is 28'-0" x 36'-0", the theory length of the ridge is 36'-0" minus 28'-0" = 8'-0" Actual Length (Cutting Length) There are two different methods of framing the hip rafters into the ridge, and which system you use, affects the length of the ridge. The two methods of framing the hips are as follows: 1. Single Cheek Cut The single check cut method has the hips framing into the side of the ridge at a 45 degree angle (see Figure 1). (see the Figure "Single Cheek Cut" in the textbook, Carpentry) The centre lines of the hip line up with the start and end of the theory length of the ridge (see Figure 1). FRMG 202/222 Roof Framing LO2 Page 69

76 Figure 1: Single Cheek Cut The hip rafter must have full bearing on the ridge so we must add some extra material at each end. The amount we add to each end of the ridge is one-half the 45 degree thickness of the hip, (which is inches at each end) plus one-half the 90 degree thickness of the ridge at each end. Formula: Actual Lengthof Ridge = RidgeTheory Length Thickness of Hip+ 290 Thickness of (single cheek eachend eachend If you are framing with 2 inch stock for hips and ridge, the formula is as follows: Ridge Theory Length + 2 ( ") + 2 (¾") When framing hip roofs it is very important that you remember the 45 degree thickness of 2 inch stock is 2⅛ inches. If you draw a 45 degree line across the edge of a 2 6 and measure it, it will measure 2⅛ inches. 45 degree thickness of 2" stock = 2⅛ inches One half the 45 degree thickness is inches. FRMG 202/222 Roof Framing LO2 Page 70

77 2. Double Cheek Cut The double cheek cut on a hip is a more common method of framing a hip roof. With a double cheek cut the hip rafters frames into the sides of common rafters, and not the ridge as the single cheek cut did (see Figure 2) (see the Figure "Double Cheek Cut" in the textbook, Carpentry). Figure 2: Double Cheek Cut For the double cheek cut, the actual or cutting length of the ridge is established by adding one-half the 90 degree thickness of a common rafter to each end, to the theory length of the ridge. Actual Lengthof Ridge = RidgeTheory Length Thickness of (double cheek cut) Common each end Or if you are framing with 2 inch stock for hips and ridge, just add 1½ inches to the theory lengths for the ridge. FRMG 202/222 Roof Framing LO2 Page 71

78 1.3 Instruction Sheet The Hip Rafter The hip rafter runs from the rafter or wall plate, to the ridge at a 45 degrees angle, when viewed in plan view (from above). The hip rafter is required to be at least 2 inches (50 mm) greater in depth than the commons, to support the hip jacks. Calculating the Line Length of a Hip Rafter There are two methods of calculating the line length of hip rafters and hip rafter tails: 1. hypotenuse of the total run and total rise (square root method), and 2. rafter table method from the framing square. Square Root Method By knowing the total run and the total rise of the hip rafter, where the hip rafter becomes the hypotenuse of the triangle, use the square root method to determine the line length of the hip rafter (see Figure 3). Figure 3 Line length of hip rafter shown in Figure 3 (square root method). FRMG 202/222 Roof Framing LO2 Page 72

79 The horizontal run of the hip feet The total rise of hip rafter is same as the common roof slope, 14 units of run for the common 14 4" = 56" or 4'-8" (4.67') Now we have a right angled triangle that has a base of ft and a height of 4.67 ft. (see Figure 3). Theory Line Length of the hip feet or 20' 4 " 1 8 Rafter Table Method For calculation purposes, the hip rafter has the same number of units of run as the common rafter. In Figure 4 you see a square 1'-0" 1'-0", or 1 unit of run for a common rafter. If you calculate the diagonal, it will be inches. Figure 4 The 17 inches is used when laying out the hip with the framing square. Seventeen (17) is the set point for the hip, just as 12 is the set point for the common. On the framing square, on the body where the rafter tables are shown find length of hip or valley per foot of run. The rest is the same as for the common. If the roof slope is 4 12 look under the 4 and across from "LENGTH OF HIP" and you will see the unit of line length for the hip is inches (see Figure 6). FRMG 202/222 Roof Framing LO2 Page 73

80 This number is determined by finding the square root of a triangle with a base of 17" and a height of 4" (see Figure 5). Figure 5: Unit-of-Line Length Figure 6: Imperial Framing Square Example: Calculate the line length of a hip rafter for the following building: building size 22'-0" 32'-0" roof slope 5 12 Number of units of run for hip (same as common) is 11 Unit of line length for a hip (from framing square) for a 5 12 Theory line length of hip = " = " = 16' slope, is 17.69" FRMG 202/222 Roof Framing LO2 Page 74

81 Calculating the Line Length of the Hip Rafter Tail The same method is used to find the line length of the hip rafter tail that we used on the hip. Example: roof overhang 2'-0" roof slope 4 12 Line length of hip rafter tail = 2 units of run 17.44" (from framing square) = 34.88" = 2' " Plumb and Seat Cuts The set point on the framing square is 17 inches for hips. If you were laying out a plumb cut on a hip rafter for a 4 12 roof slope, use 17 and 4 on the framing square (see Figure 7). Mark along the tongue for a plumb cut, and along the body for a seat cut. Deductions on Hip Rafters Figure 7: Laying Out Plumb Cut For the single cheek cut hip, the hip rafter must be shortened at the top. one-half the 45 thickness of the ridge (see Figure 8) For a double cheek cut hip, the hip rafter must be shortened at the top. one-half the 45 thickness of the common rafter stock (see Figure 8) FRMG 202/222 Roof Framing LO2 Page 75

82 Figure 8 Deduction for Rough Fascia The rough fascia is part of the overhang. The hip needs the fascia in the corner, at a 45 angle. The deduction for the rough fascia: full 45 thickness of rough fascia (see Figure 9) Figure 9 Laying Out Side Cuts on the Hip Rafter If the hip rafters meet the ridge board and fascia as in a flat roof, the side cuts on the hips would be 45 degrees. However, as the slope of the roof increases, the angle of the side cut increases. The figures to use for any roof slope are shown on the bottom line of the table on the rafter square. Find the line in the table on the square that is labelled "Side Cut of Hip or Valley Use" and then look under the unit of rise number, same as for the common rafter (see Figure 10). Example: From the framing square, the number to use for laying out side cuts for a hip with a 4 12 slope, is FRMG 202/222 Roof Framing LO2 Page 76

83 Use this figure with 12 inches on the framing square to lay out the side cut on top of the hip (see Figure 10). always mark on the 12" side (on the larger of the two numbers) Figure 10 If using a double cheek cut, flip the square over and lay out another angle using the same numbers. When cutting side cuts, set the circular saw at a 45 level, and because you are cutting a compound angle, the angle will be correct. Dropping or Backing the Hip If you take the measurement from the birdsmouth to the top of the common rafter and use the same depth on the hip, when you go to install the sheathing, the edges of the hip rafter are too high. The reason for this is that the centre line of the hip is at the correct height, but the edges are high (see Figure 11). This problem can be corrected in one of two ways: 1. backing the hip, or 2. dropping the hip. FRMG 202/222 Roof Framing LO2 Page 77

84 Figure 11 To back the hip is to bevel the top edge of the hip rafter at the proper angle, from ridge to facia. This requires a lot of work (see Figure 11). The amount that you back the hip can be calculated using the following formula: Formula: Unit of Rise 1 2 Unit of Run o Amount to Back a Hip Rafter (or Dropa Hip)= Thicknessof Hip(90 ) Example: For a 4 12 slope 4.75 ( 3 3 4") or 16 (on both sides)(see Figure12) It is much easier to drop the hip. Dropping the hip involves cutting the birdsmouth deeper so that the edges of the hip are at the right height (see Figure 12). To drop the hip first draw the plumb line at the birdsmouth (see Figure 12). next layout a side cut on top of the birdsmouth (see Figure 12) drop a plumb line down from this side cut line (in front of first plumb line) measure the height of material above birdsmouth same as on common rafter on this new plumb line (see Figure 12) draw seat cut in back to first plumb line the birdsmouth will be much larger than on the common rafter FRMG 202/222 Roof Framing LO2 Page 78

85 Figure 12: Dropping the Hip at the Birdsmouth An alternate method of dropping the hip is using the following formula (same formula as backing the hip). Formula: Unit of Rise Amount of Drop for the Hip= Unit of Run o 1 2 (90 )Thicknessof Hip 4 Example: For a 4 12 slope.75( 3 3 4") or 16" To drop the hip, lay out the birdsmouth, then measure up ¼ inch and make the birdsmouth deeper (see Figure 13). Figure 13: Alternate Method of Dropping the Hip FRMG 202/222 Roof Framing LO2 Page 79

86 Alignment of Hip to Ridge When nailing the hip at the top, to the commons (tripod gable), the edges of the hip are made flush with the commons (see Figure 14). The top point of the hip is lower than the ridge. 1.4 Review Exercise Figure How would you calculate the theory length of a ridge board on a hip roof? 2. What is the theory length of the ridge for a hip roof for a building 28'-0" 38'-0", 4 12 slope, 2'-0" overhang? 3. What additions are added to the theory length of a ridge to get the actual length for: a. single cheek cut b. double cheek cut FRMG 202/222 Roof Framing LO2 Page 80

87 4. What is the actual length of the ridge for the following buildings? a. building - 26'-0" 40'-0" slope overhang - 16" single cheek cut all framing 1½" thick stock b. building - 24'-0" 28'-0" slope overhang - 24" all framing 1½" thick stock double cheek cut 5. What is the line length per unit of run for a hip rafter on a roof with a 5 12 slope? 6. How many units of run are there in a roof on a building 26'-0" 40'-0" for the following: a. the common rafter b. the hip rafter 7. The set point of 17" (16.97) is used to lay out a hip rafter. How is the number obtained? 8. Common rafters should be laid out before the hips. Why? 9. Calculate the following, when given: building - 22'-0" 28'-0" slope overhang - 24" single cheek cut all framing 1½" stock a. hip rafter line length b. hip rafter tail line length FRMG 202/222 Roof Framing LO2 Page 81

88 10. Calculate the following, when given: building - 28'-0" 44'-0" slope overhang - 20" double cheek cut all framing 1½" stock a. hip rafter theory length b. hip rafter tail line length 11. Two reasons why the hip rafter stock should be one size larger (in depth) than the common rafter stock. 12. Why should the ridge be one size larger stock than the commons? 13. What is "backing" a hip? 14. How is a hip rafter "dropped"? 15. How much should be deducted at the top of a hip rafter, if all framing material is 1½" thick, for the following: a. single cheek cut b. double cheek cut FRMG 202/222 Roof Framing LO2 Page 82

89 a b c d e f g h i Slope 1:4 1:2.4 1:3 1:2 1:1.71 1:1.5 1:4 1:3 1:2.4 Span 30'-0" 24'-0" 26'-0" 30'-0" 28'-0" 24'-0" 22'-0" 18'-0" 21'-0" Run Units of Run Unit of Rise Unit of Line Length Plumb Cut on Framing Square & & & & & & & & & Line Length of Hip Rafter Overhang Projection 24" 16" 24" 18" 12" 16" 6" 16" 14" Line Length of Overhang 16. Using the steel square tables, fill in the blanks for the following hip rafters. FRMG 202/222 Roof Framing LO2 Page 83

90 17. How much is deducted at the rafter tail on a hip, for the rough facia (2 6)? 18. When laying out a side cut on a hip rafter, what numbers would you use on the framing square, for the following slopes a and b and 19. When laying out side cuts on a hip rafter, which number or side of the framing square do you mark along? 1.5 Practical Exercise Lay Out a Hip Rafter Resources Required 1. building size 18'-0" 24'-0" 2. double cheek cut 3. roof slope overhang 24" 5. rough facia and ridge amount of rafter above birdsmouth on common 2½" 7. 16'-0" 2 4 stock (for ease of handling in shop) Directions 1. Layout the hip rafter showing all deductions and cut lines. Procedures Steps 1. Calculate line length of hip rafter and rafter tail. Key Points FRMG 202/222 Roof Framing LO2 Page 84 using calculator and framing square tables 2. Layout top plumb line at top of rafter. crown up use set point of 17" square across top of rafter

91 Steps Key Points 3. Measure line length of hip and rafter tail. along top of rafter square across top of rafter see Figure Lay out plumb line at birdsmouth and facia. use set point of 17" 5. Lay out deduction at top. measure ½ 45 thickness of common rafter, on side of hip see Figure 15 draw new plumb line Steps Figure 15: Layout of a Hip Rafter Key Points 6. Lay out double cheek cut at top. square across top of rafter at deduction plumb line, then bisect the squared line use side cut figure from square mark on larger number side, through bisected point see Figure Draw two new plumb lines at top. from side cut lines see Figure 15 mark these "cut lines" 8. Lay out birdsmouth. depth of rafter above birdsmouth to be same as common rafters (2½" for this rafter) see Figure 15 FRMG 202/222 Roof Framing LO2 Page 85

92 Steps Key Points 9. Drop the hip. calculate amount of drop needed draw new seat cut see Figure Deduct for rough facia. along side of rafter 45 thickness of rough facia (2⅛") see Figure Lay out side cuts for facia. use side cut figures from square through bisected line see Figure Lay out two new plumb lines at facia. mark as cut lines see Figure Mark all cut lines. 14. Print your name on rafter tail. 15. Have your instructor check your work. Learning Step 2 Calculate and Lay Out Hip Jack Rafters and Assemble Hip Roof Components 2.1 Reading Assignment From the textbook, Carpentry, study the chapter "Hip Roofs." 2.2 Reading Assignment The Hip Jack Rafter Hip jack rafters are shortened common rafters that run from the plate to the hip. They have the same spacings and slope as the common rafters. The birdsmouth and rafter tail of a hip jack are the same as the common rafter (see Figure 16). The hip jack meets the hip at a 45 angle (plan view) and, therefore, require a side cut at the top end. Hip jacks are cut in pairs (one left and one right) and there are four pairs of hip jacks for each length, in a rectangular hip roof. FRMG 202/222 Roof Framing LO2 Page 86

93 Figure 16: Hip Jack Rafters Run of Hip Jack Rafter Unit-of-run is 12 inches (same as the common rafter). Total Run - the run of a hip jack rafter is always equal to its distance from the corner of the building (see Figure 17). Figure 17: Hip Jack Rafter Run of Hip Jack Rafter #1 is equal to distance x. Run of Hip Jack Rafter #2 is equal to distance y. Formula: Spacing of Hip Jacks Run of Hip Jack = distance hip jack is from corner of building Hip jacks have the same spacings as the common rafters. The centres are calculated from "the first common rafter" and work towards the corner of the building. The shortest hip jack may not be at an even rafter spacing from the corner of the building. Hip jacks are laid out in this manner for easier sheathing application. FRMG 202/222 Roof Framing LO2 Page 87

94 Units of Run for Hip Jacks The line length per foot of run of a hip jack is the same as a common rafter, so use the common rafter lengths on the framing square. Remember, the total run of the hip jack is its distance from the corner of the building, to the centre of the hip jack. In Figure 18, the common rafters are spaced 11'-0" from the corner of the building, to the centre of the rafter. The rafters are on 16 inch centres. The run of the longest jack is its distance from the corner, 11'-0" minus 1'-4" = 9'-8" or 9.67' therefore we have 9.67 units of run (for the longest hip jack). Line Length of Hip Jacks Figure 18: Spacing of Hip Jacks The unit of line length for a hip jack is the same as for the common rafter (with the same slope). On the framing square, find the unit of line length, or ULL for the common rafter, and use it for the jacks. Example: Building shown in Figure 18 Roof slope 1 4 Find the line length of the longest hip jack. We have already calculated how many units of run, the hip jack has (which is 9.67 units of run). The number of units of run for the longest jack rafter = 9.67 The unit of line length (same as for the common rafter) = 12.65" The line length of the hip jack rafter = " = = 10' FRMG 202/222 Roof Framing LO2 Page 88

95 Common Difference of Hip Jacks The "common difference" of hip jacks is a term used for the amount which a hip jack is either longer or shorter than the preceding hip jack rafter (see Figure 19). The "common difference" can be found on the framing square on the line mm difference in length of jacks 16" centers or 24" under the figure for inches rise per foot of run. For example in Figure 18 the jacks are on 16" centres and the roof slope is On the framing square look under 4 inches, across from difference in length of jacks 16" centres and you will find ". That means the second longest jack is " shorter than the longest jacks. The same is true for all the remaining jacks. Figure 19 Formula for Finding Common Difference If you want to find the common difference of jacks using math, the following is used. Formula: ULL O.C.Spacing of Jacks Common Difference of Hip Jacks = Unit - of - Run FRMG 202/222 Roof Framing LO2 Page 89

96 Example: Roof slope 4 12 Rafter spacing 16" O.C. Solution The framing square gives the common difference as ", 1 16 " difference from the math method. This is usually caused by converting from fractions to decimals and back again. Figure 20: Common Difference of Hip Jacks Plumb Cuts, Birdsmouths, and Hip Jack Rafter Tails The hip jack is similar to the common rafter, so all plumb cuts and seat cuts are laid out the same as a common rafter. Remember to use the set point 12" now, not 17" as you did on the hip. For a 4 12 roof slope, use 4 and 12 for plumb and seat cuts. The rafter tail is identical to a common rafter. FRMG 202/222 Roof Framing LO2 Page 90

97 Deductions on the Hip Jack Rafter The theory line length of the hip jack measures to the centre line on the hip rafter (see Figure 21). Figure 21 The amount of deduction at the top of the hip jack is 1 2 the 45 degree thickness of the hip. Remember this deduction is measured on the side of the rafter, not on top (see Figure 22). Side Cuts for Hip Jack Rafters Figure 22: Side Cut at Top of Hip Jack The hip jack requires an angled cut (side cut) at the top, where it meets the hip rafter. The required side cut figure is obtained from the rafter square tables. Look across from "side cut of jacks use" and under the unit of rise for the roof. FRMG 202/222 Roof Framing LO2 Page 91

98 Example: For a 4 12 slope, look under 4" and find ". To lay out the side, cut at the top of the jack use " and 12" and mark along the largest number side (12"). Remember the side cut is laid out through the centre theory line on top of the rafter. After the deduction is made on the side of the jack, square across the top of the rafter and bisect this squared line (cut in half) (see Figure 22). 2.3 Review Exercise 1. The common difference in length of hip jacks for a 5 12 slope at 24 inches on centre is inches. 2. The common difference of hips jacks for a 3 12 slope at 16 inches on centre inches. 3. How many units of run does a hip jack have, if the jack is 4'-6" from the corner of the building? 4. What is the line length of a hip jack rafter that is 64 inches in from the corner of the building with a 4 12 slope? 5. Calculate the line length of the second longest hip jack in a hip roof with a 5 12 slope and rafters spaced at 16" O.C., building size 24'-0" 30'-0". 6. What figures on the framing square are used to layout the side cut for a hip jack with a 4 12 slope. 7. How many pairs of hip jacks are cut to the same length for a hip roof on a rectangular shaped building? 8. The hip jack is shortened at the top by deducting. 9. What is the set point for a plumb-cut on a hip jack? FRMG 202/222 Roof Framing LO2 Page 92

99 10. How is the birdsmouth for a hip jack laid out? 11. Calculate the theory lengths for the hip jacks for the following hip roof: building size - 28'-0" 42'-0" roof slope rafters - 24" O.C. overhang 2'-0" a. line length of longest hip jack b. line length of shortest hip jack c. line length of third longest hip jack 2.4 Practical Exercise Lay Out a Hip Jack Rafter Resources Required 1. building size 8'-0" 10'-0" 2. roof slope rafters 16" O.C rafter stock 5. framing square rough facia and ridge Directions 1. Lay out the longest hip jack rafter for the above roof. FRMG 202/222 Roof Framing LO2 Page 93

100 Procedures Steps Key Points 1. Calculate line lengths. of hip jack rafter and tail use framing square tables 2. Select material. 2 4 stock 3. Lay out top theory line and plumb line. crown up use 12" set point for plumb cut square across top see Figure 23 Steps Figure 23: Layout Top Plumb Cut 4. Lay out line length of rafter. square top of rafter see Figure 24 Key Points 5. Lay out line length of rafter tail. again square across top of stock see Figure Lay out birdsmouth. same as common use rule for depth 7. Lay out plumb cut at birdsmouth. see Figure Lay out deduction for rough facia. measure 1½" deduction on side of rafter, at 90 to plumb line see Figure 24 Figure 24: Hip Jack Layout FRMG 202/222 Roof Framing LO2 Page 94

101 Steps Key Points 9. Lay out deduction for hip at top. measure ½ 45 thickness of hip or " along side of rafter draw new plumb line see Figure Square top of rafter at hip deduction plumb line. bisect the squared line see Figure Draw a side cut at top. for hip through bisected point, or centre line use side cut figure on square mark on largest number side (12") see Figure Draw new plumb line at top. to line up with side cut on top see Figure 24 mark as "cut" line 13. Have your instructor check your layout. Criteria: All items must be checked yes for attainment. 1. Line length of rafter is correct (± 1 16 "). 2. Line length of rafter tail is correct (± 1 16 "). 3. All plumb lines correct angle and location. 4. Birdsmouth correct size and location. 5. Deduction for rough facia is correct. 6. Deduction for hip is correct. 7. Side cut for hip is correct. 2.5 Practical Exercise Lay Out a Hip Jack Rafter Pattern Resources Required 1. building size 24'-0" 36'-0" 2. overhang 24" 3. roof slope rafter stock rough facia and ridge 6. rafters at 16 inches O.C. Yes No No FRMG 202/222 Roof Framing LO2 Page 95

102 Directions 1. Lay out a common rafter, item lay out the longest hip jack, then all the remaining jacks, on the common rafter. Procedures: Steps 1. Calculate line length of common rafter and tail. for above building Key Points 2. Calculate line length of longest hip jack. find common difference of jacks from framing square deduct common difference from theory length of common rafter see Figure Lay out plumb line for jack. on side of rafter 4. Deduct for hip. ½ 45 thickness of hip ( ") on side of rafter draw new plumb line see Figure 25 Note: Once the deduction is made for the longest jack, do not take it off again for remaining jacks. Steps 5. Calculate line length of common rafter and tail. Figure 25: Laying Out Remaining Hip Jacks Key Points FRMG 202/222 Roof Framing LO2 Page 96 for above building 6. Lay out side cut for jack. through bisected point angle can go either way (doesn't matter) 7. Square new line on top of rafter. at longest point of sidecut see Figure 25

103 Steps Key Points 8. From this squared line, lay out next jack. use common difference do not lay out sidecuts at this time square across top 9. Lay out remaining jacks. until birdsmouth is reached 10. Number the hip jacks. 1, 2, 3, 4 etc see Figure 25 To use this pattern, you don't cut it out. Just lay another piece of rafter stock against the pattern, square across top at birdsmouth, rafter tail and the long point of which ever jack you need. Then draw plumb cuts through these three points and the hip jack is ready to cut. Criteria: All items must be checked yes for attainment. 1. Line length of common rafter is correct. 2. Line length of rafter tail is correct. 3. Line length of longest hip jack is correct. 4. Deduction for hip is correct. 5. Sidecut for hip jack is correct. 6. Top of rafter squared across at longest point of jack. 7. Remaining hip jacks laid out correctly. 8. Hip jacks numbered. 9. Birdsmouth laid out correctly. 10. Deduction for rough facia is correct. Yes No No FRMG 202/222 Roof Framing LO2 Page 97

104 FRMG 202/222 Roof Framing LO2 Page 98

105 Performance Test 3 Construct a Hip Roof Name: Student ID: Date: Given 1. building size 12'-0" 13'-4" 2. roof slope overhang 1'-0" 4. rafter stock x 6 rough facia, ridge, hips 6. rafters 16" O.C. 7. double-cheek cut on hips Directions 1. This test will be constructed on top of the walls you framed up in a previous test. The gable roof has been removed and some of the common rafters were saved to use in this test. 2. You will construct one-quarter of the hip roof on the building. The ridge is calculated, cut and erected as a group project. Then you will individually cut and install one hip rafter and all the hip jacks on that hip. You will also install the rough facia on your part of the roof. Procedure Steps Key Points 1. Calculate length of ridge. double cheek cut as a group project 2. Cut and install ridge. as a group project use six common rafters from previous test make sure birdsmouth are all the same depth and the rafters are identical FRMG 202/222 Roof Framing LO2 Page 99

106 Figure 26: Hip Roof Test Note: The three common rafters used at each end of the ridge, to support the ridge, are sometimes called the "Tripod Common." Steps Key Points 3. Calculate, lay out, and cut hips. drop the hip at birdsmouth see Figure Install hip rafter. nail as per NBC 5. Calculate, lay out, and cut longest hip jacks. jacks 16 inches on centre 6. Install longest hip jacks. long points must be directly opposite each other at hip, square line across top of hip to check alignment do both sides of hip with jacks at same time FRMG 202/222 Roof Framing LO2 Page 100

107 Steps Key Points 7. Cut and install remaining jacks. check for 16" centres check for alignment by placing straightedge on top of rafters keep hip rafter straight 8. Check rafter tails for alignment. with straight-edge or string line 9. Cut and install rough facia. align with top of rafters check for straight 10. Print your name on hip rafter tail. on top of hip 11. Have your instructor check your work. 12. Dismantle hip roof. square ends of material before putting in storage 13. Remove ceiling joists and rafter plates. see instructor for storage location 14. Dismantle steel stud partitions. leave exterior walls up for next performance test Criteria: All items must be checked yes for attainment. 1. Ridge is correct length (±⅛"). 2. Common rafters installed correctly at ridge. 3. Commons in correct location on rafter plates. 4. Nailing is correct on commons. 5. Line length of hip rafter and tail correct (± 1 16 "). 6. Birdsmouth on hip "dropped." 7. Hip proper height at ridge. 8. Side cuts and plumb cut at ridge are correct. 9. Hip centred on corner of building. 10. Hip nailed correctly (NBC). 11. Hip jacks at correct on-centres (±⅛"). 12. Hip jack line-lengths are correct (± 1 16 "). 13. Deduction for hip on hip jacks is correct. 14. Side cut on jacks is correct. 15. Plumb cut on jacks is correct. Yes No Mark FRMG 202/222 Roof Framing LO2 Page 101

108 16. Birdsmouth on jacks are correct. 17. Alignment of tops of rafters (over birdsmouth) is good. 18. Alignment of rafter tails is good. 19. Rough facia at correct height. 20. Rough facia nailed correctly. 21. Roof overhang is correct (±⅛"). 22. Kept work area clean and safe. 23. Used ladders safely. 24. Dismantled roof safely. 25. Cleaned up all material and stored neatly. 26. Worked co-operatively with others on roof. Mark Yes No Mark Comments: FRMG 202/222 Roof Framing LO2 Page 102

109 Performance Test 4 Lay Out a Hip Rafter, Hip Jack, and Ridge Name: Student ID: Date: Given 1. 16'-0" - 2 4's 2. framing square 3. tape measure Directions 1. At the end of this course you will be required to lay out a a. hip rafter, b. hip jack rafter, and c. ridge (double cheek cut) for a given building. 2. Your instructor will give you the necessary information and checklist when you start the test. Criteria: All items must be checked yes for attainment. 1. The performance test will be available from the instructor when you are prepared to complete it. FRMG 202/222 Roof Framing LO2 Page 103

110 FRMG 202/222 Roof Framing LO2 Page 104

111 Learning Outcome 3 Assemble Engineered Roof Trusses and Install Sheathing Learning Step 1 Identify Types of Roof Trusses and List Advantages of Using Trusses 1.1 Reading Assignment Study the following: from the textbook, Carpentry, study "Roof Trusses" from the textbook, Canadian Wood-Frame House Construction, study "Ceiling and Roof Framing." 1.2 Instruction Sheet Roof Trusses It is important that a carpenter has an understanding of the principles of the roof truss. You must know the parts of a truss and how they are assembled. The carpenter should know the reasons for having different truss designs. The actual designing of trusses is done by engineers. A roof truss is a composite structural component in a roof. The truss is composed of a framework of several members. The members are arranged in such a manner that they form a series of triangles. Trusses are the standard method of roof construction. Wood trusses are used in residential, agricultural and light commercial buildings. Wood trusses are also used in flat roofs because of their capability of long spans and accommodation of higher insulation levels. Although many truss designs are available, we will discuss the more commonly used ones in residential construction. These include king post truss, Fink truss, scissor truss, Howe truss, attic truss, flat truss, mono truss, and cantilever truss. FRMG 202/222 Roof Framing LO3 Page 105

112 King Post Truss The king post is the simplest of all trusses. It consists of upper and lower chords and a centre vertical post. Because the allowable spans are much less than other trusses, it is used mainly on small buildings such as small residential garages (see Figure 1). Fink Truss (W Truss) Figure 1: King Post Truss The W truss is one of the most common and widely used of all light wood trusses. Its design includes more members than the king post truss, so the distance between the connections is less: giving better support to the top and bottom chord. The Fink truss has a maximum span of 26'-0". Scissor Truss Figure 2: Fink Truss The scissor truss is used for houses with a sloping ceiling. It is more complicated than the W- type truss. It provides good roof construction for a cathedral ceiling, using less material than conventional framing methods. The bottom slope is half of the slope of the top chord. Howe Truss Figure 3: Scissor or Vaulted Truss The Howe truss is used where more bottom chord support is required for longer spans. Figure 4: Howe Truss FRMG 202/222 Roof Framing LO3 Page 106

113 Attic Truss The attic truss is designed for one and one-half storey houses where storage or rooms are required in the attic. Parallel Chord Trusses These trusses create sloped ceilings. Figure 5: Attic Truss Figure 6 FRMG 202/222 Roof Framing LO3 Page 107

114 Mono Truss The mono truss is a single slope truss, sometimes used on garage or carport additions. Flat Top Truss for Hip Roofs Figure 7: Mono Trusses The flat top truss is used when framing a hip roof (sometimes referred to as a "cottage" roof). Studio Vaulted Truss Figure 8: Cottage or Flat Top Truss This truss is engineered to accommodate different ceiling features. Parts of a Truss Figure 9: Studio Vaulted Truss The illustration below shows a typical roof truss and all its components. Figure 10: Parts of a Truss FRMG 202/222 Roof Framing LO3 Page 108

115 Truss Connectors (for Timber Construction) A major problem encountered in the efficient use of wood trusses was the method of fastening the members together. Truss connectors are used to fasten and hold members of a truss together. Truss connectors, along with tight fitting joints, prevent the members from sliding when loaded. If the members are allowed to move, deflection will occur in the top and bottom chords. The first connection breakthrough was the split-ring timber connection, which is still used in long span trusses. Figure 11 Metal plate connectors are the most commonly used type of connector. The plates may have drilled holes through which nails are driven into the truss. When nailing plates are used, the engineer specifies the size, gauge, and the number of nails used in each truss joint. Figure 12: Nailing Plate A more common truss connector is the gang-nail. It is stamped in such a way that a series of holes is punched in the metal, producing sharp, tooth-like spikes. The galvanized steel plates are pressed into the wood members that are pre-cut and assembled on a jig. FRMG 202/222 Roof Framing LO3 Page 109

116 Figure 13: Gang Nail Truss Connector Using Roof Trusses There are several advantages to using roof trusses. 1. Speed of Erection Since trusses are preassembled, they can be erected much more quickly than the conventional roof systems. 2. Efficiency A truss requires less lumber for a given span than does conventional framing. Trusses are often placed at 24" O.C. instead of the 16" spacing of conventional framing members. 3. Flexibility Roof trusses allow for more flexible floor planning as no bearing partition or beams are required for support. There are also disadvantages of using roof trusses. 1. Truss Uplift Separation cracks between ceilings and interior partitions often occur in buildings using roof trusses. As we put more and more insulation in our attics, we cause a problem called truss uplift. In cold weather, the bottom chords of the trusses are covered with insulation and are kept warm in a heated building. The top chords are cold and take on moisture, while the bottom chords are warm and dry. The top chords expand due to the moisture, resulting in the trusses bowing upwards in the centre portion. As the bottom chord bows upward, the joint between the wall and ceiling drywall is opened up creating an unsightly crack. This crack can be prevented by "floating" the drywall at the corners. If the bottom chord has been securely fastened to the partitions, the entire partition may be lifted, causing doors in the wall to not work properly, and leaving a gap between the wall and floor. As the outdoor temperatures warm up, the trusses return to their original position. FRMG 202/222 Roof Framing LO3 Page 110

117 Roof Designs Roof trusses come in many designs, which are used for different roof framing situations. At one time trusses were restricted mainly to gable or flat roofs. Because of improved fastening devices and connector plates, different types of hip and intersecting roofs have been designed. Before we discuss various roof truss designs, we will identify two very important aspects of their construction. These are 1. tension and compression, and 2. weight and stress. Stresses on Roof Truss Components The following figure shows a typical roof truss and the types of stresses on all its components. It is important to note that most stress on a connecting plate or plywood gusset is shear pressure; therefore the type, length, gauge, and location of fasteners is critical. Tension and Compression Figure 14: Stress on Roof Trusses All the parts of trusses are either in compression or tension. The ones in compression are subjected to a pushing-together force. The ones in tension are subjected to a pull-apart force. The balance between the two gives the truss the ability to carry the load over a wide span. Weight and Stress Trusses must be designed to carry the weight of materials used for the framing, sheathing, roofing materials, ceiling finishes, and snow load. Because the bottom chord supports the ceiling, these members must be designed to withstand deflection within allowable limits. It must be noted here that all roof truss designs must be determined by professional engineers. There are a variety of truss designs and details available for prefabrication, however, approval must be assured by the authority having jurisdiction. When prefabricating roof trusses, all material, layout, connectors and fastening, as indicated, must be rigidly adhered to. FRMG 202/222 Roof Framing LO3 Page 111

118 Now, we will discuss the following types of roof design: gable roof, hip roof, intersecting roof trusses, and low heel and high heel trusses. Gable Roof The standard gable roof is the simplest of all, with gable end trusses at both ends and common trusses between them, usually spaced at 24 inches O.C. Common trusses become special trusses under unusual loading arrangements, such as a heavy weight suspended from the bottom chord. A typical gable end roof is shown in the following figure. Hip Roof Figure 15: Gable Truss Roof Hip roofs can be framed more economically and quickly using a hip roof truss package. The systems vary depending on the manufacturer (see Figures 16 and 17). Figure 16: Components of a Hip Roof Truss Package FRMG 202/222 Roof Framing LO3 Page 112

119 Components of a Hip Roof Truss Package Common Truss Figure 17 The number of common trusses will depend on the type of corner package used. The 8'-0" corner package is most common. Girder Truss The girder truss is used to support the hip and the corner packages. It usually has a larger bottom chord than the common truss. The girder truss is used for various spans. Most hip roof truss packages use a standard girder truss which can accommodate spans up to 60'-0". Since most corner packages use 8'-0" as a base unit, the girder truss for roofs with spans over 16'-0" have flat tops (see Figure 17). The length of the flat portion can be calculated by multiplying the size of the corner package times two and then subtracting the result from the span of the truss. Example: truss span 28'-0" 8'-0" corner package 28'-0" minus (2 8'-0") = 12'-0" flat portion Hip Truss The location of the hip trusses is between the girder and common truss (see Figures 16 and 17). The hip truss is a modified regular truss with a flat top on it. Mono Truss Mono trusses are used from the girder truss to the end wall. A mono truss is used where the corner package meets the girder truss (see Figures 16 and 17). FRMG 202/222 Roof Framing LO3 Page 113

120 Hip Rafter The hip rafter is framed the same as in conventional framing, and is framed into the mono truss and the girder truss. It is usually a 2 6 (see Figure 18). Figure 18: Hip Intersection Figure 19: Girder Truss Corner Package Figure 20: Mono Truss Locations The size of the corner package depends on the manufacturer, and consists of end wall jacks and side wall jacks. End Wall Jacks End wall jacks are usually installed first, starting with the longest one (top chord). The bottom chord is framed into the girder, and a framing anchor is used to fasten it to the girder truss. FRMG 202/222 Roof Framing LO3 Page 114

121 Figure 21: End Wall Jacks Anchored to the Girder Truss Commercial Application Side Wall Jacks The side wall jacks are usually installed after the end wall jacks, starting with the longest one (top chord). Hip Blocks The hip blocks are usually supplied with the package. If not, they are calculated the same way as the hip rafter. To ensure proper alignment, a string line can be used. Blocks (to extend ridge and/or rafter) Blocks are usually supplied with the package, but if not can be calculated the same way as a common rafter. When nailing the blocks to extend the top chord of the end wall jacks, care must be taken to ensure proper alignment. Figure 22: Rafter Extension FRMG 202/222 Roof Framing LO3 Page 115

122 Ridge Extension It is not necessary to position a common truss at the exact point of hip rafter and ridge intersection. A ridge extension block may be used instead and will save the cost of a common truss. Intersecting Roof Trusses Figure 23: Ridge Extension Block The intersecting roof requires common trusses as well as other types (see Figures 24 and 25). A girder truss is usually needed to support the trusses. Figure 24: Components of an Intersecting Roof FRMG 202/222 Roof Framing LO3 Page 116

123 Figure 25: Intersecting Roof Trusses Truss hangers are fastened to the bottom chord of the girder to support the ends of the common trusses (see Figure 26). Figure 26: Cross-Section of Girder and Valley Trusses When trusses are used on the main and minor roof, conventional framing should not be used for the valley portion. It may cause point loading on some of the trusses which may result in excessive deflection and ceiling cracks. Valley trusses allow the load to be distributed evenly at 24" O.C. There are several details important to the design and/or construction of any type of roof truss. We will discuss them briefly. FRMG 202/222 Roof Framing LO3 Page 117

124 Location of Jobsite It is extremely important that your truss fabricator knows the location of your jobsite. Snow loads vary greatly from one part of the country to another. Snow loads can sometimes double in a distance of 32 km (20 miles). Authority Having Jurisdiction Many municipalities do not follow the National Building Code in its entirety. They may have special loading or testing requirements which will affect the type of truss supplied. It is absolutely essential that you get your truss drawings approved by the authority having jurisdiction before fabrication of the trusses. Special Loading Requirements Advise your fabricator of any special load requirements such as attic loads, air conditioners, cranes, etc. that are to be supported by the roof system. Also specify if any heavy type of roofing or ceiling material is to be applied to the trusses. Type of Building Design requirements and safety factors vary depending on whether the building is residential, commercial, and industrial or farm. It is recommended that you supply your truss fabricator with a set of building plans for any project. This is absolutely essential on commercial and industrial jobs since a simple difference of elevation between two sections of roof can result in much greater load requirements on the lower section due to snow drifting. Bearing Points It is normally assumed that trusses are supported at the ends of the bottom chord. This is not true in all cases. There may be a cantilever condition which means the bearing point is some distance from the end of the bottom chord. This drastically changes stresses and must be specially designed. Sometimes flat trusses or monopitch trusses are hung from the top chord. This also requires special design considerations so your fabricator must be made aware of the bearing locations. Slope, Pitch, and Bevel All these terms are used to describe the slope of the roof. Spacing Trusses are normally spaced 24 inches on centre but sometimes it is more practical to put them on 16 inch or 48 inch centres. Trusses will be greatly overstressed if they are spaced further apart than they were designed to be. FRMG 202/222 Roof Framing LO3 Page 118

125 Truss Drawings It is recommended that you obtain from your fabricator a copy of the truss drawing, since it will show the minimum bracing requirements necessary to ensure the structural integrity of the roof system. Bracing is the responsibility of the contractor and if not done properly will void any warranties or guarantees. Low Heel and High Heel Trusses Figure 28 shows a low heel truss that was commonly used until we began to super insulate our roof spaces and walls. As can be seen in the illustrations, the high heel truss (Figure 29) allows for maximum insulation to completely cover the top plate of the exterior wall, and still allow air passage for ventilation of the roof space (attic). Figure 27: Raised Heel for Increased Insulation Figure 28: Low Heel Truss (Agricultural) Figure 29: High Heel Truss FRMG 202/222 Roof Framing LO3 Page 119

126 Truss Support Options With proper planning and communication, roof trusses can be engineered to accommodate special requirements. In order to avoid bulk heads to hide structure members, the engineer can bury the structural members by modifying bearing points on the truss. The following three figures are examples of these modifications. 1.3 Review Exercise Figure 30 Identify the following trusses: 1. The truss illustrated below is a. Figure 31 FRMG 202/222 Roof Framing LO3 Page 120

127 2. The truss illustrated below is a. Figure The truss illustrated below is a. Figure The truss illustrated below is a. Figure The truss illustrated below is a. Figure 35 FRMG 202/222 Roof Framing LO3 Page 121

128 6. The truss illustrated below is a. Figure The truss illustrated below is a. Figure The truss illustrated below is a. Figure The truss illustrated below is a. Figure A member extending from one end of a truss to its peak, forming the top of the truss is the. 11. A member extending from one end of a truss to the opposite end, forming the bottom edge of the truss is the. 12. Vertical or diagonal members joining top and bottom chords are the. 13. The horizontal distance between supports is the. 14. The intersection point of the top and bottom chord is the. FRMG 202/222 Roof Framing LO3 Page 122

129 15. The movement of truss members due to dead and live loads is. 16. Any permanent load, such as the weight of the truss members, sheathing, and shingles, is the. 17. Any temporary load, such as snow, wind, and construction loads is the. 18. The point of intersection where web members meet a chord is the. 19. The chord segment between panel points is the. 20. The horizontal distance between panel points is the. 21. The point at which two chord members are joined together to form a single member is the. 22. The point where the sloped top chords meet is the. 23. The upward vertical displacement built into a truss to compensate for deflection is the 24. The extension of a truss beyond the outside support is the. 25. The structural part of a truss extending beyond its support is the. 26. Drawings checked, approved and sealed by a professional engineer are. 27. The plywood used to connect truss parts together is the. 28. Using the illustration below, identify the following points and parts of a truss. a. b. c. d. e. f. Figure 40 FRMG 202/222 Roof Framing LO3 Page 123

130 Determine whether each of the following statement(s) is true or false. 29. T F A truss is composed of triangles. 30. T F A cantilevered truss is one that has the support back from its normal position. 31. The components of trusses are either in or stresses. 32. What are some items to consider in "dead load"? 33. What is the most common "live load" on roof trusses? 34. Common trusses are usually placed at inches O.C. 35. For hip roofs, the girder truss is used to support the and the. 36. Most corner packages use foot as a base unit, so the girder truss with spans of over 16'-0" have flat tops. 37. Under what circumstance will a common truss become a special truss? 38. In a hip roof using roof trusses, a truss is used where the corner package is supported. 39. How is the length of the flat portion of the girder truss calculated? FRMG 202/222 Roof Framing LO3 Page 124

131 Learning Step 2 Install Roof Trusses 2.1 Instruction Sheet Installing Roof Trusses Roof trusses must be installed according to their design, and be plumbed and braced in position until the roof sheathing and all permanent bracing is in place. Proper Erection of Trusses Trusses have a great deal of strength when they are placed in a vertical position and properly braced and sheathed. However, they can be easily damaged or broken if they are racked or stressed in the lateral direction. It is important that they be handled very carefully in order to prevent overstressing during transporting and erection. Unloading Trusses Trusses should be unloaded by the fabricator or custom hauler onto relatively level, dry ground. They should not be unloaded onto rough terrain that would cause excessive lateral strains which would distort the trusses. Dumping of small trusses is allowed provided they are not damaged. Banding of the trusses into bundles is desirable when dumping is practical. Erecting Small Trusses Figure 41: Storage of Trusses Trusses may be erected by hand provided that care is taken to prevent excessive lateral strain when sliding trusses over the walls and when tipping them upright on the walls. It may require one or two persons as shown in the following figure to accomplish the tipping-up operation to reduce lateral deflection of the members. FRMG 202/222 Roof Framing LO3 Page 125

132 Erecting Large Trusses 36 to 50 Feet Figure 42: Erection of Small Trusses Larger trusses should be erected by mechanical means (forklift, crane, etc.). Adequate slings and/or spreader bars must be used to prevent lateral strain. At least two pick-up points are required. Do not permit cutting, drilling, or damage of the chords or webs. Do not remove webs (even temporarily). Do not make field repairs to damaged trusses without approval of manufacturer. Do not overload single or groups of trusses with plywood, roofing, or other construction materials or tools. It is extremely important that a rope be tied to the truss or group of trusses so it can be guided to the proper position on the top plate or wall. Erecting Long Span Trusses 50 Feet The longer the truss, the greater the care necessary to prevent lateral strain. Use of a strongback is recommended for spans over 50 feet. The strongback may be any material with rigidity and good bending strength (pipe, steel "I" beam, heavy timber, etc.). It should be tied to the truss at intervals not to exceed 10 feet and should be two-thirds or three-quarters as long as the truss. The strongback should be tied to the truss above mid-height to prevent overturning. FRMG 202/222 Roof Framing LO3 Page 126

133 Figure 43: Erection of Larger Trusses Figure 44: Erection of Long Span Trusses Erecting Field-Spliced Trusses and Trusses Over 60 Feet Gang-Nail recommends building the roof in sections on the ground, complete with the bracing, and lifting onto the walls by crane. The following graphics by Gang-Nail Truss will explain the proper procedure. FRMG 202/222 Roof Framing LO3 Page 127

134 Figure 45 FRMG 202/222 Roof Framing LO3 Page 128

135 Proper Bracing of Trusses There are two distinct types of bracing - "temporary" and "permanent." Each is important and plays a major role in the structural integrity of the roof system. Temporary Bracing Most truss failures occur during or immediately after erection usually from a gust of wind. The cause is inadequate temporary bracing. The trusses merely fall over or domino because they have not been adequately tied to the supporting structure or to each other. It is the contractor's responsibility to ensure that this doesn't happen. The first step is to brace the first truss (or gable) that is erected to the supporting structure or ground. The first truss is thus held vertical and straight. The second truss to be erected must be held the correct distance from the first by means of spacers. This can be done with short pieces of 1 4 or 2 4. These spacers also act as lateral braces for the top chord, until the sheathing is applied. Figure 46: Temporary Bracing Once three or four trusses are erected, they should be cross-braced starting near the base of the end truss to the peak of the third or fourth truss along the vertical king post. This prevents the trusses from being blown over. FRMG 202/222 Roof Framing LO3 Page 129

136 Figure 47: Temporary Bracing For large spans or long buildings it is recommended that permanent bracing and roof sheathing begin as soon as a sufficient number of trusses are erected. This will stabilize the structure dramatically making it safer to continue erecting more trusses. Never leave trusses overnight without all temporary and permanent bracing being properly applied. Never overload the trusses by applying concentrated loads such as roof sheathing and shingles in one spot. Permanent Bracing Figure 48: Truss Elevation Permanent bracing includes roof sheathing or purlins and any bracing details shown on the engineered truss drawings. It also includes any bracing specified by the designer of the building. This is an important point since the truss designer may not have seen the building plans and is not familiar with site conditions. The person has designed only the truss and is specifying only the bracing required for vertical load transfer of the truss. The designer of the building may specify additional bracing because they may have additional information such as prevailing wind conditions, height, and length of walls, etc. FRMG 202/222 Roof Framing LO3 Page 130

137 There are three main types of permanent bracing that may be specified on the engineered truss drawings. These are continuous braces, diagonal braces, and T-braces. You can expect to find these specified for a truss when it has very long tension webs, webs in heavy compression, or chords in compression that are not fully supported. Long-span trusses will have diagonal bracing specified at midspan. For very long spans the truss will often have diagonal bracing specified at the one-quarter span points as well as the midspan. The purpose of this bracing is to achieve a greater stability within the trusses and to help develop a load-sharing system. The following figure shows some examples of common bracing situations. The last trusses to the gable end are shown. Figure 49: Residential Kingpost With Cantilever FRMG 202/222 Roof Framing LO3 Page 131

138 The common Howe shown above has only the long diagonal web braced with a continuous brace. Note that the last three trusses at each end should also be diagonally braced on the underside of this web. This is done to take out lateral forces that may develop in the continuous bracing and should be done in all instances where continuous braces are specified, whether they be on compression or tension webs. Commercial Figure 50: Commercial Another instance of diagonal bracing may be found at the centre of the truss illustrated above. These are applied once again at about 45 to the trusses and on both sides of the web. On some drawings, this type of bracing may be named "X" bracing. Note again that the last three trusses have a diagonal brace on the underside of the continuously braced web. In most other cases, the bracing specified will be a variation of those already illustrated. For example, if the top chord of a truss will not be sheathed because of framing above it or perhaps a piggyback truss attached to the top chord of it as in the case of high pitch trusses built in two pieces (see Figure 52). In both these cases, the underside of the top chord will have to be braced with continuous braces at 460 mm on centre. FRMG 202/222 Roof Framing LO3 Page 132

139 Figure 51: Piggy-Back Truss (Residential) This same bracing may be called for on the underside of the top chord of trusses that have large top chord sizes. Due to the bending of the top chord, it is possible to get the outside fibres on the bottom of the top chord into compression. The result is a buckling condition which causes lateral movement that must be resisted. It is possible to have continuous braces specified on the bottom chord as well. One case of this occurs where the truss is cantilevered a large amount and sagging must be prevented. Another case is on the bottom chord of a three hinged arch where no sheathing will be applied to this compression chord (see the previous figure). It should be pointed out that all braces specified on the engineered drawings are structural requirements of the truss and the truss will not perform as the drawing indicates unless they are installed. Braces may be eliminated by the use of sheathing only when specified on the drawing and providing that the sheathing and fastenings can take out the lateral forces. Figure 52: Three-Hinged Arch (Commercial) Collapse can easily occur without a bracing system that will prevent both horizontal sway or roll over (see the following figures). By rolling on their sides, where they have no strength, the trusses will break or pull the ends off the bearings. Figure 53: Horizontal Sway Figure 54: Roll Over FRMG 202/222 Roof Framing LO3 Page 133

140 All trusses are unstable laterally until properly braced. The longer the span, the more care required. Adequate restraint is necessary at all stages of construction. Complete stability is not achieved until the bracing and decking is completely installed and properly fastened. Erection, bracing and procedures as well as the safety of the workers are the responsibility of the erector. When properly aligned, each top chord should not vary more than one-half inch from a straight line (see Figure 53). Without proper bracing, trusses may not support even their own weight. The vertical alignment cannot be more than one-quarter of an inch out of plumb. Size of Braces and Fasteners Figure 55 Unless otherwise stated on the drawing, braces used on residential trusses must be 1 x 4 and on commercial and farm trusses, 2 4. Exceptions to this rule occur in commercial and farm trusses where large spacing of trusses is allowed and the size of the bracing must be increased accordingly. 1 4 braces are to be fastened to each member crossed with two - 2" nails minimum. 2 4 braces are to be fastened to each member crossed with two - 3½" nails minimum. In special cases where larger than 2 4 braces are required, the exact brace size will be specified on the truss drawing and consequently, larger nails will be required. Tiedown For residential trusses it is normally satisfactory to fasten the truss to the supporting wall by means of three 3¼" toenails at each end. This is best accomplished by driving the nails through the holes in the truss plate at approximately a 30 angle. Some jurisdictions will require tie downs on all roof structures. FRMG 202/222 Roof Framing LO3 Page 134

141 Figure 56: Typical Bearing Detail For commercial, industrial, and farm buildings the trusses may receive wind uplift when large doors are opened. In situations like this it is advisable to use metal tiedowns as in the following figure. Handle and Erect Wood Trusses Figure 57: Typical Bearing Details While the recommendations for handling, erection and bracing stated here are technically sound, it is not intended that they be considered the only method for erecting and bracing a roof system. Neither should these recommendations be interpreted as superior to nor a standard that would necessarily be preferred in lieu of an architect's or engineer's method for erection or design for bracing a particular roof system. These recommendations originate from the collective experience of leading technical personnel in the wood truss industry, but must, due to the nature of responsibilities involved, be presented only as a guide for the use of qualified building designer, builder or erection contractor. Thus, the Truss Plate Institute of Canada and W.W.T.A. expressly disclaims any responsibility for damages arising from the use, application, or reliance on the recommendations and information contained herein by building designers or by erection contractors. Note: Trusses must be in a vertical plane to take advantage of their superior ability to support loads. On the Ground Directions: (Erection) 1. Check trusses to ensure that none have been broken or damaged during delivery. 2. Confirm that the correct number and types of trusses have been delivered. FRMG 202/222 Roof Framing LO3 Page 135

142 3. Measure trusses to ensure that they are built to required pitch and span, and are constructed to include any special details such as cantilevers, etc. Figure 58: Strong Truss Figure 59: Weak Truss The truss erector or the builder shall take the necessary precautions to ensure that the erection procedures and handling methods do not damage the trusses and, thus, reduce their load-carrying capacity. Install Gable Roof Trusses Directions 1. Check the trusses to ensure they have not been broken or damaged. 2. Lay out truss centres on the walls. 3. Lift trusses on the wall taking care not to bend or twist them. Trusses have very little lateral strength and can be damaged if not handled properly (see Figure 59). If the trusses carry a marking ensure that the markings are all on the same side of the building. If the trusses are not too large they can be lifted by hand or with a rope at each end. The trusses can sit on top of the partitions, keeping all the peaks in the same direction and overlap (see Figure 60). If there are no partitions, the trusses can be set upside down with the ends resting on the plates, until they are ready to swing into place. Figure 60: Raising Trusses FRMG 202/222 Roof Framing LO3 Page 136

143 4. Erect the gable end or end trusses and brace them. Place gable end sections on one end wall; plywood sheathing will extend down over the top wall. If the gable is in sections, the sections will now be nailed together. Nail the sheathing to the top plate. Be sure that the top chords of each section are in line at the peak. Nail to the top wall plate; plumb and brace the gable end (see Figures 61 and 62). Figure Ladders Figure 62 To install ladders, place one truss flat on the top of walls and partitions. Place one ladder section on the top chord of the truss, then place the second ladder on the other top chord. Align the two at the peak. Securely nail, being careful to keep the top of the ladder in line with the top of the top chord of the truss. Tilt up the truss with the ladder framework over the top of the gable end. Plumb the truss and check for proper overhang. Level the ladders by using shims between the lookouts and the gable end (see Figure 61). 6. Trusses After the gable ends and ladders are installed, check the gable end for plumb, and check the overhang on the gable end. The trusses may now be installed. Care should be taken in marking the rafter plates to assure that roof sheathing joints will occur over a truss. Also, chimney openings and attic access openings must be allowed for. The trusses may be placed upside down hanging on the two outside walls, or resting on the partitions. FRMG 202/222 Roof Framing LO3 Page 137

144 A building line and spacers may be attached to the tail of the truss at each end of the building and all trusses are aligned and spaced to this line. Usually three workers install trusses: one at each wall to fasten trusses to wall plates, and the third swings them up from below. 7. Plumb and brace each truss as it is set into place. Use temporary braces on top of trusses, until roof sheathing is applied. Once several trusses are up, start the permanent bracing inside the trusses. On large roofs, it may be necessary to install the roof sheathing on the trusses go up, for bracing. 8. Install truss tie downs if required. These may be a framing anchor or joist anchors, or metal strap. 9. Do not nail the trusses to the interior partitions. One 2" nail may be used to tack the bottom chord to the partition to keep the truss aligned. However, do not securely toe-nail the truss to the interior walls as this may cause lifting of the wall due to truss uplift. Framing a Hip Roof With an 8'-0" Corner Package Directions Figure Install the cottage hip girder with the outside face 7' " from the end wall. 2. Install the first A jack with its face 7' " from the side wall. FRMG 202/222 Roof Framing LO3 Page 138

145 3. If the 2" 6" corner jack has a wedge cut to a point for a block, the top plate has to be shaved off at the pitch of the corner jack to allow the block to sit flat on the wall plates. 4. Install the corner jack with the shoulder but on the high end bevel flush with the top of the sloping section of the hip girder. This point should be " from the intersection of the sloping and horizontal top chords. The point of the corner jack will be below the height of the horizontal top chord. This distance varies with pitch. 5. Install the B, C, and D jacks at 24" O.C. with the bottom chords running through to the bottom of the cottage hip girder. 6. Install the B1, C1, and D1 jacks at 24" O.C. with the 1' " bottom chord back nailed through the bottom chord of the D jack. 7. Align the top chords of the jacks to maintain 24" O.C. spacing and nail to the 2" 6" corner jack with the shoulder of the bevel flush with the top of the corner jack. 8. Install the 2" 6" sub fascia, top outside edge of the 2" 6" in line with the top plane of the jacks. 9. Install the E blocks. Install Intersecting Roof Trusses Directions 1. Measure and install the girder truss. Plumb and brace as required. 2. Lay out the rafter centres on the bottom chord of the truss and install hangers. 3. Cut the rafter tails from the required number of trusses, depending on the layout on the girder truss, if they are not already cut off the truss plant. 4. Install common trusses, gable ends, etc. on the main roof. 5. Install common trusses, gable ends, etc. on the minor roof. 6. Apply sheathing on the main roof. Leave an opening for access from the main attic space to the minor attic space, and for ventilation. 7. Determine the point of intersection of valleys (see Figure 64). Use a string line or straightedge and level to determine the elevation point where valleys intersect (see Figure 64). Use a string line to determine the horizontal location (line up the peaks of the common trusses of the minor roof) (see Figure 64). FRMG 202/222 Roof Framing LO3 Page 139

146 8. Snap chalk lines for the valley trusses from the point determined in Step (see Figure 65). 9. Install the valley trusses (see Figure 65). Ensure proper alignment with a string line (see Figure 65). Each valley truss must be nailed with two 3½" nails to each truss underneath. 10. Install permanent bracing and blocking. Figure 64: Determine Point of Intersection of Valleys on Main Roof Figure 65: Point of Intersection Figure 66: Valley Trusses FRMG 202/222 Roof Framing LO3 Page 140

147 2.2 Instruction Sheet Roof Sheathing The purpose of roof sheathing is to close in the roof, provide backing for the roof covering, and brace the roof system. The carpenter will be expected to select, install, and determine the sheathing requirements of a roof. Roof Sheathing Lumber Types shiplap common boards tongue and groove Method of Application 1. Lumber is applied to the roof at right angles to the rafters. 2. Butt joint on rafters must be staggered, as shown in the following figure. 3. Nailing - refer to the National Building Code of Canada. 4. Boards wider than 11¼ inches (286 mm) should not be used for roof sheathing. Figure 67: Lumber Sheathing FRMG 202/222 Roof Framing LO3 Page 141

148 Sheet Material Types Various types of sheathing are mentioned in the Building Code. Thicknesses and rafter spacings must conform to the National Building Code of Canada. Applying Sheet Material 1. Measure the width of the sheets from outside the fascia or ½ inch over the fascia at both ends of the roof. It's usually better to keep the sheathing flush and let the roof edge flashing project over for a drip edge. If the sheathing hangs over, it tends to absorb moisture and deteriorate. 2. Snap a chalk line across these points. 3. Plywood should be placed with the face grain at right angles to the rafters. Oriented strandboard should be placed with the direction of face orientation, as marked on the sheets, at right angles to the rafters. 4. Install the first sheet with the top along the chalk line. 5. Butt the rest of the sheets the same way (leaving a 1 16 inch gap between abutted edges for expansion). 6. Ensure that all rafters are on centre. (They might have to be pushed slightly and then nailed.) Check the on-centre location of rafters by tape. 7. Drive one nail into each rafter. This will hold the rafters and tell you where to nail later on. 8. Supply some form of edge support before applying the second row, if required. Edge support: 2 2 or 2 4 blocks between rafters or metal "H" clips. (See "Notes" below.) 9. Apply the second row, staggering all joints. 10. Apply the rest of the sheathing, always allowing 1/16" minimum for expansion. 11. Nail according to the National Building Code of Canada. 12. Usually, the sheets are allowed to hang over on the overhangs and are all cut together when all the sheets have been installed. FRMG 202/222 Roof Framing LO3 Page 142

149 Notes: 1. If metal or vinyl fascia will be installed, or if a vinyl or metal drip edge will be used, the roof sheathing is placed flush with the rough fascia, otherwise the roof sheathing projects ½ mm beyond the finish fascia. Figure "H clips" are aluminum clips shaped like an "H" and are approximately ¾" wide (see Figure 68). They are inserted into the plywood edges at mid rafter spacing to give strength to the joist (see Figure 69). Figure 69: Plywood Sheathing FRMG 202/222 Roof Framing LO3 Page 143

150 2.3 Review Exercise 1. Trusses should be stored on ground. 2. When trusses are unloaded by dumping, they should be to prevent them from being damaged. 3. When hoisting roof trusses by crane, at least pick up points are required. 4. For spans over 50 feet, a is recommended to reduce lateral strain. 5. The spacers used when erecting roof trusses serve two purposes. Name them. 6. Once three or four roof trusses are erected, they should be to prevent being blown over. 7. For large spans or long buildings, it is recommended that and begin as soon as possible to brace the roof trusses. 8. What are the three main types of permanent bracing that may be specified on the engineered truss drawings? 9. The most common method of fastening the roof trusses to the top plate is by. 10. Hip roof systems can be constructed with roof trusses by the use of pre-manufactured. 11. How does moving a supporting bearing wall under a truss, affect the truss design? 12. What precautions should be taken when unloading and handling trusses? FRMG 202/222 Roof Framing LO3 Page 144

151 13. How can trusses be overloaded when installing them? 14. Why is permanent bracing required on trusses? 15. Explain how to brace the first three trusses when starting to put up trusses. 16. What are three general rules that apply to trusses as far as drilling, notching, or modifying them? 17. The NBC states that if the length of any compression web in a truss exceeds m (or ft), the web shall be braced to prevent buckling. 18. Minimum size of bracing for trusses is. 19. Boards wider than may not be used for roof sheathing. 20. Plywood roof sheathing should be laid with the face grain to the rafters. 21. Plywood roof sheathing must have at least nails along the 4'-0" edge of a sheet and at least nails along intermediate supports. 22. What two methods are used to support the edges of the plywood sheathing on a roof? FRMG 202/222 Roof Framing LO3 Page 145

152 23. a. All sheets for roof sheathing must be spaced at least inches apart at the joints. b. The reason for allowing this space is for. 24. What two conditions must apply to the end joints when sheathing a roof with lumber? 25. Give the minimum thickness of roof sheathing for the following. a. plywood sheathing, rafters spaced 16" O.C., with the edges supported inches b. OSB (O-2 grade) sheathing, 24" O.C., edges supported inches c. waferboard (R-1 grade) 24" O.C., edges unsupported inches 2.4 Practical Exercise Lay Out Roof Trusses Note: See your instructor for this practical exercise. Figure 70 FRMG 202/222 Roof Framing LO3 Page 146

153 FRMG 202/222 Roof Framing LO3 Page 147

154 FRMG 202/222 Roof Framing LO3 Page 148

155 Performance Test 5 Lay Out Roof Trusses Name: Student ID: Date: Given 1. 16'-0" framing square 3. tape measure Directions 1. Your instructor will give you the necessary information and checklist when you begin this performance test. FRMG 202/222 Roof Framing LO3 Page 149

156 FRMG 202/222 Roof Framing LO3 Page 150

157 Learning Outcome 4 Frame a Gable and Hip Roof Using Metric Measurements Learning Step 1 Perform Gable Roof Calculations in Metric Measurements 1.1 Instruction Sheet Lay Out a Common Rafter Using Metric In metric roof framing, the unit-of-run is 1000 mm or 1 metre, instead of 1 foot as it was in imperial. The unit of rise is expressed in millimetres (see Figure 1). Figure 1: Metric Roof Slope Symbol We will use the Stanley metric square. The rafter tables are found on the body of the square, similar to imperial (see Figure 2). In Figure 1, the unit of run is 1000 and the unit of rise is 400. Figure 2 shows part of the rafter tables on a framing square. At the left, the first line from the top gives various rises (mm) per metre of run. The rises given on the tables are 250, 300, 400, 500, and so on. From Figure 1, we will use a rise of 400. FRMG 202/222 Roof Framing LO4 Page 151

158 Figure 2: The Stanley Metric Roof Framing Square (Using a Unit Run of One Metre or 1000 mm) On the rafter table in Figure 2, the second line gives the length of common rafters per metre of run in millimetres. Find 400 in the top line and read the line length per metre of run (1077) in the second line. FRMG 202/222 Roof Framing LO4 Page 152

159 What this tells us, is that for each metre of run, the line length of a common rafter is 1077 mm (see Figure 3). Rafter Line Length Figure 3: Unit of Line Length The next step is to find out the width of the building the rafter is being laid out for. For example, let's use a building width of 9400 mm (see Figure 4). Figure 4: Span of a Building The 9400 is the span of the building. A single rafter spans only half way, which is from the outside of the building to the centre. This distance is called the run of the rafter (see Figure 4). In our sample building, the run is mm 2 The next step is to divide the run into units of run. The unit of run for a common rafter is always Therefore unitsof run 1000 Now we have 4.7 units of run for the common rafter and the unit of line length per unit of run from the rafter tables is Multiply the two together. FRMG 202/222 Roof Framing LO4 Page 153

160 = mm = 5062 mm This is the theory length of the common rafter. Rafter Tail Line Length Calculating the line length of the rafter tail is similar to the common rafter. First, determine the run of the rafter tail. In our example building (see Figure 4) the overhand is 600 mm. Therefore the run = Next, multiply the number of units of run by the unit of line length = mm = 646 m The line length of the common rafter tail is 646 mm. Total Rise of a Roof The total rise is calculated the same way as we did for imperial. In Figure 4, the run is 4700 mm. To calculate the total rise of the roof multiply. Formula: Total Rise = number of units of run unit of rise run = 4700 units of run = 4.7 unit of rise = 400 Total of rise = = 1880 mm Figure 5: Total Rise of a Roof FRMG 202/222 Roof Framing LO4 Page 154

161 Using the Metric Square for Plumb and Seat Cuts Since one metre (1000 mm) is too large a size for a framing square, the rise and run figures are reduced to fit on the square. Stanley Metric Square Both the rise and run have been reduced to 1 5 for convenience of layout. As a result, the unit of run (1000) is reduced to 200 and is marked on the body of the square, with an arrow (see Figure 6). This point is called the set point = 200 set point Figure 6: Stanley Framing Square Set Point This 200 set point is used for all common rafters. The set point is located on the outside edge of the body. The unit of rise (rise per metre) figure is found on the tongue of the square. These rise figures are located in the centre of the tongue (see Figure 7). Figure 7: Rise Figures on Square When laying out a rafter with a rise of 300 mm, locate the 300 on the centre of the tongue and go across to the outside edge of the square and you will notice the "60" mark lines up with the 300. The "60" mark would be placed on the edge of the rafter stock when laying out an angle (see Figure 7) (300 5 = 60). If the unit of run is 400, use 80 on the edge of the tongue, and so on (400 5 = 80). FRMG 202/222 Roof Framing LO4 Page 155

162 Positioning the Square To position the square on the framing material to lay out a plumb or a seat cut, first lay the stock, (e.g., 2 4), on the flat, crown edge away from you. Position the 200 set point along the bottom edge of the stock (see Figure 8). Position the rise figure (on the tongue) along the same edge of the stock. Figure 8: Laying Out a Common Rafter These same figures are used to lay out plumb cuts and seat cuts at the birdsmouth and rafter tail. Deductions for Ridge The amount of deduction depends upon the thickness of the ridge board. The deduction is always one-half the thickness of the ridge board. As an example let's use a ridge board (which is 38 mm thick). The deduction at the top is therefore 38 divided by 2 = 19 mm. This deduction must be taken off at right angles to the plumb line on the side of the rafter (not on top of rafter) (see Figure 9). Deduction for Facia The amount of deduction again depends on the thickness of the rough facia (usually 38 mm thick). The deduction is always the full thickness of the facia. This deduction is again taken off of the side of the rafter, not on top (see Figure 10). FRMG 202/222 Roof Framing LO4 Page 156

163 Figure 9: Deduction for Ridge Figure 10: Deduction for Rough Fascia 1.2 Instruction Sheet Lay Out Gable End Studs Using Metric To calculate the line length of gable end studs, we use the same formula as before. Formula: runof stud unit of rise L.L.of Gable End Studs = 1000 Example: (see the following figure) Figure 11: Deductions on Gable End Studs FRMG 202/222 Roof Framing LO4 Page 157

164 In Figure 11, the theory length of the stud is mm This is the theory length or mathematical length only. This theory length is the height from the top of the double top plate to the theory line of the common rafter at the birdsmouth. To get the actual cutting length of the gable end stud, two deductions must be made at the top. One deduction is for the top plate, which because it runs on an angle, it is more than 38 mm thick when measuring vertically. To get this thickness, draw a angle on a and measure the thickness along this angle. (e.g., a at a slope is 41 mm thick) (see Figure 11). The other deduction is the vertical height of the birdsmouth. You get that from the common rafter. Remember, this height of 720 is through the centre of the stud, not on the stud edges. Then through this centre point, lay out the roof slope angle. FRMG 202/222 Roof Framing LO4 Page 158

165 a b c d e f g h i Slope 1:2.5 1:3.33 1:1.67 1:2 1:1.43 1:3.33 1:4 1:1.25 1:1 Span Run Number of Units of Run Unit of Rise Unit of Line Length Line Length of Rafter Overhang Projection Line Length of Overhang Total Rise of Roof 1.3 Review Exercise 1. Using the steel square rafter tables and performing the necessary calculations, fill in the blanks for the following common rafters. FRMG 202/222 Roof Framing LO4 Page 159

166 1.4 Practical Exercise Lay Out a Common Rafter Using Metric Measurements Resources Required 1. building size gable roof 3. roof slope overhang 400 mm 5. rough facia ridge '-0" Stanley metric framing square 9. pair sawhorses Directions 1. On a 16'-0" 2 4, lay out the common rafter with all deductions shown. Procedures Steps Key Points 1. Calculate the line length of rafter and tail. using your calculator and framing square tables 2. Lay out plumb cut at top slope square across crown edge of Measure theory length of common rafter. along crown edge 4. Draw plumb line at birdsmouth. square across top of rafter see Figure Measure theory length of rafter tail. along crown edge 6. Draw plumb line at facia. see Figure 12 FRMG 202/222 Roof Framing LO4 Page 160

167 Steps Figure 12: Layout of a Common Rafter Key Points 7. Measure and lay out deduction for ridge. deduction to be measured on side of rafter mark cut line see Figure Measure depth of birdsmouth. ⅓-⅔ rule draw seat cut 9. Measure and laid out deduction for facia. mark cut line see Figure Put your name on the rafter tail. 11. Have your instructor check your work. Criteria: All items must be checked yes for attainment. 1. Top plumb was cut at the correct angle. 2. Line length of common rafter was correct ±2 mm. 3. Line length of rafter tail was correct ±2 mm. 4. Deduction for ridge was correct. 5. Birdsmouth depth was correct. 6. Birdsmouth seat cut was correct. 7. Deduction for facia was correct. 8. Crown was up on rafter. 9. Layout was neat and easy to follow. Yes No No FRMG 202/222 Roof Framing LO4 Page 161

168 Learning Step 2 Perform Hip Rafter Calculations Using Metric 2.1 Instruction Sheet Lay Out a Hip Roof Using Metric Unit-of-Run for Hips The unit-of-run for a common rafter is This measurement is too large to use on a framing square. Therefore, 1 5 of 1000 is taken and the set point of 200 is used on the framing square to lay out a common rafter. For a hip rafter the unit-or-run is , which is the diagonal of a square that is 1 metre square (see Figure 13). Figure 13: Unit-of-Run for a Hip Rafter FRMG 202/222 Roof Framing LO4 Page 162

169 Again, 1414 is too large to use on a framing square so 1 5 is taken and a new set point of 283 is marked on the framing square (see Figure 14). Figure 14: Metric Framing Square FRMG 202/222 Roof Framing LO4 Page 163

170 Calculate the Line Length of a Hip Rafter First determine the number of units of run for the hip rafter. Remember a hip rafter has the same number of units of run as the common rafter. Example: building size roof slope overhang The run is The number of units or run is The unit of line length from the framing square for a slope for the hip rafter is 1470 mm (see Figure 14). 4. theory length = 4.2 units of run 1470 = 6174 mm 5. The rafter tail has or.6 units of run. 6. Theory length of rater tail is = 882 mm. Ridge Boards for Hip Roofs The theory length of the ridge is length of building minus width of building. The cutting length (or actual length) is calculated the same as for imperial roofs. Single Cheek Cut Add one half the 90 thickness of the ridge board stock plus one half the diagonal (45 ) thickness of the hip rafter stock to each end of the theory length of the ridge board (see Figure 15). Note: The 90 thickness of a 2 6 ridge is 38 mm. The 45 thickness of 38 mm stock is 54 mm. One- half the 45 thickness is 27 mm. FRMG 202/222 Roof Framing LO4 Page 164

171 Figure 15 Double Cheek Cut For a double cheek cut add one-half the 90 thickness of the common rafter to each end of the theory length of the ridge (see Figure 16). Deductions for Ridge and Facia Figure 16 The hip rafter must be "shortened" if a ridge board is used. Similarly the rafter tail must be shortened if a fascia is used. Ridge Board Deduction The ridge board occupies a part of the run of the hip rafters. The ridge and the hip rafter meet at an angle of 45, therefore, the shortening required is half the diagonal thickness of the stock. This amount is measured on the hip rafter stock at right angles to the plumb cut (see Figure 17). FRMG 202/222 Roof Framing LO4 Page 165

172 Figure 17 Deduction for Fascia The fascia occupies a portion of the run of the overhang. The hip rafter meets the fascia at an angle of 45, therefore, the deduction required is the diagonal thickness of the fascia stock. This also is measured at a right angle to the plumb cut (see Figure 18). Side Cuts for Hip Rafters Figure 18 The figures to use for the side cuts for any slope is shown on the bottom line of the table on the rafter square. Always look under the unit rise of the roof. Example: 1:2.5 slope (400 mm rise per metre) On the bottom line on the table under 400 mm, rise per metre run is 208. Use this number 208 mm, and 200 mm, to mark the side cut on the top edge of the hip rafter stock. Note: The bottom line on the rafter square reads, "SIDE CUT OF HIP OR VALLEY USE OPP. 200 mm LINE." This means use the figure under the unit of run (in this case 208) and 200 (see Figure 19). FRMG 202/222 Roof Framing LO4 Page 166

173 You will find that you always mark side cuts on the larger of the two numbers. Dropping the Hip Figure 19 The amount to drop the hip is calculated the same as for Imperial rafters. Here we will use the formula: Formula: unit of rise Amount to Dropa Hip= unit of run 1 o 2 90 thicknessof hip Example: For a slope, the amount to drop is calculated Line Length of Hip Jack Rafter The run of the hip jack rafter is its distance from the corner of the building. If a hip jack is 2400 mm from the corner of the building to the centre of the hip jack, its run is also 2400 mm. Therefore, it will have 2.4 units of run Use the unit of line length of the framing square for the common rafter. The deduction at the top is ½ the 45 thickness of the hip or 27 mm. The sidecut figure is also found on the framing square under "sidecut of jacks." The "common difference in length of jacks" is also given on the square tables. FRMG 202/222 Roof Framing LO4 Page 167