Fortified For Safer Living

Transcription

1 Fortified For Safer Living Module 18: The Roof Sheathing Inspection Inspection Two is the sheathing inspection. In this inspection, we re going to check to be sure that the roof deck is the proper thickness, and that it s attached with the correct fasteners at the correct spacing. As you learned previously, these are critical to good performance in high winds. Nail size and nail spacing, in particular, are the two most important things in the strength of a roof deck. Nail Size and Spacing The plan reviewer will identify for the inspector any specifications that are different from the standard items listed below. One of these standard specifications is 8d ring-shank nails on 6-inch spacing. Now if the nails heads are not visible from the top of the roof because somebody s already covered them up, then you re going to have to use the stud finder with a metal locator to determine the spacing. This inspection is intended to be done after the sheathing is completely nailed off. In many cases, the roofer s going to want to get the roof watertight, so secondary water resistance may have been installed. And if they re using the self-adhesive test system, then you might be able to see the nail spacing and the tape going on at the same time, and that would be a good thing. Another method of providing secondary water resistance is the use of a fully adhered membrane, and that s stuck down completely so you can t see any nail spacing. Yet another approach is one of the new highperformance roof underlayments. If you didn t get there in time to see the nailing, then you re going to have to look at it from the inside using a metal detector on the rafters. Checking panel thickness. Well first of all, you can go in and confirm the thickness of the roof deck by measuring it with a steel ruler (slipped between two panels from underneath). The recommendation here is to measure the thickness away from the H-clip so that you measure only deck thickness. But a second very acceptable method is to look at the grading stamp, as that tells you the size of the underlayment, and you can determine whether it s the right one or not from that. It s critical to have the right size material and fasteners because keeping the roof sheathing on 2008 IBHS or its affiliates, All Rights Reserved Module 18, Page 1

2 reduces losses by as much as 30%. So that s one of the major areas of focus in a Fortified home. Checking for missed fasteners. We don t find too many people using screws but if somebody wants to use screws, a #8 X screw is acceptable. You can pretty much only confirm those from the outside because if a screw misses the truss, then the roofers typically know that and will take it out. So you typically won t see any missed screws. Staples or smooth-shank nails are not acceptable at all. The photograph at left shows an example of what a missed nail looks like in a dimensional lumber roof deck. We don t find too many people using dimensional lumber decks anymore, but as you learned earlier, they are very strong and have high uplift resistance. So we do know some people who are beginning to use dimensional lumber again. The next photo shows an example of a missed nail with a plywood roof deck, which you can see has actually been leaking for some time because there are stains around the nail. In the Fortified program we will accept one missed nail in every 4 feet, or in other words, one missed nail per sheathing section. However, you should recognize that a missed nail can be a side splitting nail, as shown in the photo below, which is unacceptable. The missed nail on the far right is not too bad, but all of the other nails shown below are splitting out the side of the rafter. These should be driven out before the underlayment goes on top and reinstalled so that there are no missed nails showing. If you came across a set of rafters that had this many missed nails, you would reject that inspection. That house would have to get fixed before you 2008 IBHS or its affiliates, All Rights Reserved Module 18, Page 2

3 could go on. Checking nail spacing. Again, normally the deck nailing is 6 inches on all locations, on the edges and in the field. In some cases, some 4-inch spacing may be required, but for the most part, it s every 6 inches with 8d ring-shank nails. If you can t observe the nails from the outside, then use the MetalliScanner. It is very useful for finding nails we can t see with our naked eye from the outside of the building. If you ve never heard of this tool, don t worry. When you buy the scanner, it comes with a full set of instructions. You re going to look at some field and edge rafters or trusses to determine the spacing. When you check edge connections, you ll actually find nails may be as close together as 3 inches. That s because there are two sheets of plywood together there and a 6-inch spacing, so the roofers may have offset the nails or may not have you don t know for sure. To use the scanner, hold it up to the rafter, zero it out, and then scan along the 4 feet of a sheathing panel. Don t move the scanner back and forth, just move it in one direction steadily across the section. Otherwise, the scanner s going to get messed up and won t tell you what the actual locations are. Each time the scanner beeps, you should mark the truss with a marking pen. When you re finished, you can take the scanner down and then just measure the spacing between the black marks. The scanner is being used in the attic in the photo at right, and you can see how the inspector is scanning from right to left and how it does help to have a head-mounted flashlight. That s because if you re holding the scanner with one hand and the marking pen with the other hand you can t see very well. A head-mounted flashlight costs only between $16 and $40, and it will help you see the scanner and how the marks are going on the trusses. The photo at left shows what the scanner screen looks like. The vertical bar in the center of the screen shows you the depth of the metal and essentially when the bar is fully to the top. That means you re right on top of the metal. As you going closer to the metal you ll see a 2008 IBHS or its affiliates, All Rights Reserved Module 18, Page 3

4 plus sign, and when you re going further away you see a minus sign. And when you re within about an inch of the metal, it will beep. So you ve got three indications of where you re looking for nails or rebar. One is the depth gauge, one is the plus or minus bar, and the last is the beep. This is calibrated to read up to about 6 inches deep for a Number 4 and Number 5 rebar, and it is accurate for nails. The beep occurs about 1/2 inch after the nail, and we ve been using one for about 10 years now, so we know that they work pretty well. Summary: Roof Sheathing Inspection Trusses in place and strapped (include truss attachment on gable ends) Deck sheathing nailed as prescribed Confirm nail size, type and nail spacing Confirm sheathing dimension and structural rating Confirm workmanship (no shiners in roof and wall sheathing) Confirm piecework if any Secondary Water Barrier or membrane (confirm product) Confirm felt weight and lap if employed Confirm shingle and installation procedure Confirm bracing on all gables and dormers 2008 IBHS or its affiliates, All Rights Reserved Module 18, Page 4

5 Sample Checklists Sample Specifics: Confirm thickness of sheathing is nominal 5/8 or other specified and approved thickness ] Confirm check of deck thickness. Date: Fastener Type: Confirm nails are minimum 8d ring-shank with diameter of at least 0.113, length of at least 2-3/8 and that ring diameter is at least greater than shank diameter or other specified and approved fastener ] Confirm check fasteners used to attach deck. Date: Fastener Spacing: Confirm that nominal spacing of fasteners is 6-inches on center at edges and in middle of panels (6 and 6 spacing) with not more than one missed nail for any 4-foot segment of roof framing. ] Confirm check of fastener spacing. Date: Underlayment and Secondary water protection Confirm with builder that underlayment to be used will satisfy Fortified Criteria and how secondary water protection will be provided if not already using self adhesive tape. ] Date: Confirm with builder that ice and water shield will be installed at eaves and extend at least 2-feet past exterior insulated wall if home is located in freezing weather hazard zone. ] Date: 2008 IBHS or its affiliates, All Rights Reserved Module 18, Page 5