All roofs have a layer of plywood sheathing underneath them, which provides a base for the shingle attachment. Although the plywood typically lasts longer than most shingles and roof coverings, leaks can cause them to rot. Rotted plywood is identifiable by sinking areas of the roof or visible leaks. Damaged shingles and rotted plywood must be removed before replacing them with new plywood and roofing material. The process is straightforward but requires working at great heights.
Things You'll Need
Pry bar or shingle ripper
Sheathing-grade unsanded plywood sheet
Six penny nails
15 to 30-pound roofing felt
Set up a ladder at an even location on the ground next to the home. Climb up and walk carefully onto the roof. Use extreme caution as you walk to the rotted portion, since other areas of the roof may be weak as well.
Remove all of the shingles using a pry bar or a shingle ripper tool to detach the nails. Remove tiles and slate by prying them up from the bottom, which may cause them to break. Once the nails detach, grasp the shingles or tiles and pull them off. Discard the roofing materials, since you will install new ones later.
Cut through the black roofing felt using a utility knife and remove it until the entire rotted plywood board is exposed.
Locate the nails that secure the plywood to the roof rafters. Pry out each nail using the pry bar. Once the nails detach, grasp the rotted plywood and pull it up from the roof. Discard the old plywood.
Place a new plywood board in the same location, ensuring the ends align over roof rafters. Secure the plywood by inserting six penny nails along the rafters, spacing them every 6 inches.
Unroll new roofing felt over the new plywood and extend it at least 3 inches over each edge of the new plywood. Cut off the excess using the utility knife and secure it to the plywood using more roofing nails spaced at 18-inch intervals along the top and bottom. Then install another center row of nails along the roof felt, also spaced at 18-inch intervals.
Proceed with reinstalling new shingles, slate or tiled roofing, depending on the type of roof covering you have installed on the remainder of the home.
Use 5/16-inch thick plywood sheathing for asphalt or wood shingle roofs and use 1/2-inch plywood sheathing for slate or tiles.