Traditional materials: Timber, stone and Brick What materials are available? Technological advancements have introduced a larger selection of materials such as: Concrete blocks Structurally engineered timbers e.g. (LVL) and timber (H) beams
What factors affect Building Material Selection? Economic considerations: Manufacture or production costs Retail costs Environmental effects of the material Physical characteristics: How heavy the material is Materials strength & ability to carry loads Appearance Fire resistance/insulation properties
Components of a Tree The trunk of a tree is cone shaped Produces new wood in the form of growth rings This means that the tree grows horizontally in girth (or increases in diameter)
Types of Timber Hardwood: Usually broad leafed e.g. ironbark, brush box Timber structure consisting of hollow pipes known as vessels Jarrah pores under magnification
Timber Treatments To ensure timber durability the timber may treated in the following ways: Timber can be impregnated with chemicals to give it a resistance to insect attacks (H2 timber) Timber can be impregnated with chemicals to give it a resistance to weather (H3 Treated Pine) CCA copper chromium arsenate LOSP Light organic Solvent Preservative
Timber Strength Timber is at its strongest along the straight length of the grain Its weakest where short, wavy or cross-graining occurs or knots Timber can be laminated together in small strips to increase its strength e.g. laminated veneered lumber (LVL)
Conversion is the sawing of a log into marketable sizes Is best carried out as soon as possible after felling to reduce the loss of useable timber And reduce end splitting of the logs Define timber conversion Timber Conversion
Timber can be cut out of the log for specific functions e.g. finishing timbers may be cut to expose the best natural grain Where structural timbers are sawn to produce the longest grains and reduce excessive or abnormal shrinkage There are several ways to convert a log into marketable sizes Timber Conversion
LIVE SAWING This method produces the largest number of wide boards But control of shrinkage and warping is very difficult due to the variety of end grains produced Timber Conversion
BACK SAWING This method produces a variety of back boards Back sawing results in the end grain being seen as a series of arcs across the end grain of the board The edge has straight grain The face show the best finish Timber Conversion
QUARTER SAWN Produces the least amount of usable boards Due to cutting and re-cutting Most timber boards having short end grain arcs Straight grain along the edge and the face Timber Conversion
As timber dries out it shrinks this can lead to warping and splitting Shrinkage does not occur equal in all directions Most timbers don t shrink excessively in length Shrinkage in width and thickness can be large Shrinkage will depend on growth rings and their position in the timber Which is created by the method of conversion used Longitudinal occurs along the length of the growth rings (usually minimal) Timber Shrinkage
Timber Shrinkage Radial Shrinkage Radial is shrinkage measured across the medullary rays
Timber Shrinkage Tangential Shrinkage Shrinkage that occurs along the growth rings as seen on the end grain of back sawn boards Causing the boards to shorten (cupping) This is the most excessive form of shrinkage
Knot form where a branch passes through the tree trunk commonly found in Cypress pine flooring Collapse occurs when cells due to excessive drying out, leading to uneven shrinkage Timber Defects
Timber Defects Cupping excessive shrinkage along the long growth rings thus causing the ends to curl up along the length of the timber Wane this is missing timber along part of the edge of the timber or where bark is still present
Want similar to wane but bigger section of timber missing Spring where the timber is straight on the face side but on edge is curved Timber Defects
Bow where the timber is straight along the edge but the face has a curve Timber Defects Twist where a timber has turned over its length from a flat position
Timber Defects Gum Pockets occur where gum or resin forms between the vertical length of the growth rings and causes the fibres to part. Heart shake where the medullary rays split
Felling shake caused when a tree is cut down and it lands on a hard surface e.g. a rock Star shake Is a number of heart shakes coming from the pith Timber Defects