What are the different roof deck attachment discount categories for a wind mitigation inspection?
Friday, July 20, 2018
Because the pressure difference between the inside and outside of a home during a hurricane creates negative air pressure so strong that it can literally suck the roof sheathing off the trusses or rafters, securely attached roof sheathing is important and it gets a discount. There are four levels of discounts, from “A” (weakest attachment, lowest discount) to “C” (strongest attachment, best discount).
Let’s start with the best, the “C” discount. Beginning in October 1, 2007, roofing contractors have been required to re-nail the roof sheathing using 8d (8-penny) ringshank nails at 6-inches on center when replacing a roof, which is the “C” category. These nails are longer than 6d nails previously required, and the rings around the nail provide extra holding power (withdrawal resistance). So, if you have a newer roof, you get the “C” discount. Also, homes built since the state-wide Florida Building Code took effect on March 1, 2002, meet the “C” standard.
Photographs taken in the attic that document the roof attachment are required. The inspector finds a “shiner” (nail that is not correctly aligned and sticking of the side of the truss/rafter), and takes a photo of it with a tape measure next to it to show the length. An 8d nail will extend past the sheathing approximately two inches, and a 6d nail—which is the next lower discount level—protrudes about one-and-a-half inches. Next, the inspector finds the spacing of the nails using an electronic device and marking each nail location on the side of two truss/rafter locations, and photographing the markings, once again with a tape against the area to show spacing.
Since the inspector is required to list the weakest connection, any part of the roof has not been re-nailed to the new standard means it does not get the highest discount. The “B” discount is given when 8d nails are at six-inch nail spacing only at the edge of roof sheathing panels and 12-inch nail spacing in the field. Last, the “A” category is for 6d nails or staples.
Each of the three categories can be used for an alternative fastener type, such as adhesives or screws, that matches the uplift withdrawal rating, in psf (pounds per square foot), of that category.
Also, see our blog posts What is the difference between a toe nail, clip, single wrap, and double wrap for the wind mitigation form? and How do I get the hip roof discount for my homeowners windstorm insurance?
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