Old Roof Sheathing: Save it or Replace it?
Q: Should I get rid of old roof sheathing and replace it with plywood?
We plan to replace the roofing on our 100-year-old house with architectural asphalt shingles that can stand up to the occasional hurricane we get around here. While we're at it, should we also take off the roof's original board sheathing, which is still sound, and replace it with plywood?
—Ed and Peggy Simmer, Suffolk, VA
Tom Silva replies: There's no need to remove the board sheathing. It actually adds strength to the roof and makes it easier for roofers to do their job. Just have them nail any loose boards tight to the rafters. Then they can cover the entire roof with ½-inch plywood sheathing.
Make sure the new plywood sheets are placed so that their short edges land over a rafter and there's about a 1/8-inch gap around each sheet to allow them to expand. In hurricane country, plywood should be nailed every 6 inches into each underlying rafter using galvanized, ring-shank, 8d common nails, such as the HurriQuake nail made by Bostitch. Anything less and your roof could blow off in a storm. The underlayment and shingles have to be applied with similar care, following the requirements laid out in the local building code.