The weak link in most existing houses is in the connection of the roof sheathing to the rafters or roof trusses.
The weak link in most existing houses is in the connection of the roof sheathing to the rafters or roof trusses. There are several ways to strengthen this attachment. The cheapest and easiest is to renail or, better yet, screw down the sheathing when you replace your roof covering. This should only cost you an extra $200 to $300 for a typical house. Refastening your sheathing and undertaking the following extra measures willl provide you with significant reduction in the vulnerability of your roof to wind damage.
• When you undertake a re-roofing project, have your roofing contractor remove all of the roof covering materials, down to the sheathing. In strong wind areas, you should never add a second layer of shingles over an existing layer.
• Have the sheathing inspected for damage or decay. Replace any weak material with sheathing rated for your truss or rafter spacing (16 or 24 inch).
• Have the sheathing refastened using either 8d ring-shank nails or #8 screws 2 inches long. The nails or screws should be installed between the existing fasteners and at a spacing of not more than 6 inches between the old and new fasteners. A smaller spacing (4 to 5 inches) is recommended if the ring shank nails are used. Also, if your roof has gable end overhangs, you should have nails or screws installed at 4 inches on center on the last truss or rafter.
• Provide a backup level of water protection by installing self-adhesive roof or window flashing tape over the joints between the sheathing. Four or six-inch wide strips are readily available in 100-foot rolls for about $20 per roll. Have your roofer seal around roof deck penetrations with roof tape, sealant or asphalt roof cement. Replace boots around pipes and flashing at wall or chimney intersections as needed.
• Specify as a minimum, ASTM D 226 Type 1 (#15) asphalt impregnated felt paper underlayment with a 19 inch overlap. The felt paper should be attached using low profile capped head nails or thin metal tins and roofing nails. The tins or caps should have a minimum diameter of 1 inch. Fasteners should be installed at no more than 6 inch intervals along all seams or laps and at 12 inch spacing in the field. Off set any vertical laps 12 inches. Have metal drip flashing installed along roof edges, nailed at a minimum spacing of 10 inches on center. If your house is within 3,000 feet of salt-water, use hot-dipped galvanized fasteners for the underlayment attachment.
• Install shingles with 6 nails per shingle or as recommended by the manufacturer. Consider specifying a Dade County, Florida approved shingle. Check out BuildingCodeOnline.com for a comprehensive listing of Dade County approved building products. Use a starter course at the bottom of each slope and consider specifying hand tabbing shingles within 3 feet of roof edges. Shingles should not extend more than 1/4 to 1/2 inch beyond the edge of the roof deck.
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