Whether you are replacing your entire roof or repairing a small area, fixing rotten sections of roof decking, or sheathing, is vital to creating a sound, watertight structure. Roof decking, which is nailed to the roof's trusses, holds roofing materials, including felt paper and shingles, and also serves to stiffen your home's structure and protect it from wind.
Inspect the inside of your home for leaks. On a rainy day, look for stained drywall or wood on ceilings and in attics or crawl spaces. Remove drywall and insulation as necessary to locate water stains on the under side of roof decking. During a reroof, inspect the decking after the shingles and underlayment have been removed. Tap water-stained sections with a hammer to test their stability.
Pry up shingles around the damaged area. Each shingle is typically secured by eight nails -- four through the middle just above the tabs and four through the shingle above it. Pull up the felt paper underneath the shingles. Working your way up the roof, expose all of the rotted wood. Leave the next course of shingles intact by carefully removing the second set of four nails. During a reroof, start at the peak of the roof and remove all shingles, prying them up with a pitchfork, working your way down the roof.
Remove Rotten Wood
Set the depth of your circular saw to thickness of the roof decking. Cut away the damaged area. Pry out nails with a claw hammer or pry bar and remove the cut piece. Expose at least two trusses so that you can nail the replacement wood to them. If possible, keep the cut-out section in one piece.
Replace Roof Decking
Select plywood or oriented strand board that is the same thickness as the wood you are replacing. If you were able to keep the removed section in one piece, measure it. If not, climb the roof and measure the opening. Orient a piece of the replacement material so that its grain will run perpendicular to the roof trusses, and cut it to the dimension of the opening. Place the cut piece into the opening and secure it to the trusses with nails placed every 4 to 6 inches.
Replace Underayment and Shingles
Cover the seams between the old and new decking with bitumen tape. Lay felt paper onto the roof, overlapping the existing paper. Staple it to the roof decking or nail it with plastic-capped roofing nails. Slide new shingles under the top undisturbed course. Lift the shingle above it and nail it first through its own center, then through the center of the shingle above. Continue laying shingles in the established pattern until the entire repair is covered.