Rebuilding a Roof Deck Over a Garage

Remove the shingles by sliding a shovel beneath their edges. Position a dumpster beneath the roof where you're working so you can throw the shingles over the side of the roof and into the dumpster. Ensure that people stay away from the garage during this time. Cover the ground around the dumpster with tarps.

Tear off the felt paper from the decking and throw it over the side of the roof with the shingles.

Inspect the decking over the garage. Look for soft places in the wood, or areas that are grayish or moldy. These are the pieces of decking that you'll need to remove.

Cut through the decking, made of plywood paneling, with a circular saw to remove the part of the decking that has rotted. Use the circular saw to cut 1/16 inch past the decking itself to avoid cutting the rafters. Pull out the sliced section of decking with a pry bar. If you don't know how thick the decking is, you have the option of removing the entire panel: Pull up the panel with a pry bar or use the claw of a hammer to remove the roofing nails holding the panel in place. If you have cut a slice of panel out of the decking without removing the entire panel, enlarge the hole in the decking with the circular saw until you reach the rafters on two sides of the hole. Expose half of the rafters beneath the hole in the panel at each edge. This will give you something to nail the new piece of decking to.

Install cross members of the same dimensions as the rafters under the two sides of the hole that do not feature exposed rafters. This step applies only if you did not remove an entire panel from the roof in Step 4. Install one cross member beneath the side of the hole closest to the ridge and the other cross member beneath the side of the hole closest to the eave. The cross members will be perpendicular to the rafters, so nail each end of the cross members into the rafters. Use metal connector brackets to secure the cross members to the rafters. Once this is complete, there will be a surface for you to nail the new piece of decking into on all four sides of the hole.

Nail the new piece of plywood to the roof. If you removed an entire plywood panel from the roof, simply insert a new 4-by-8 foot panel into the hole. If you removed a small section of the panel, cut the new panel to fit inside the hole in the roof. Use a circular saw. Cut the plywood to a size 1/4 inch smaller than the dimensions of the hole in the roof. Center the plywood over the hole so that there is a 1/8-inch gap on all sides of the plywood, and nail the new plywood to the rafters beneath. Space the nails 6 inches apart around the edges of the plywood panel and 12 inches apart through the center of the panel.