Curled or loose shingles are the most common problem. Look for them especially after a windstorm. In areas where shingles overlap, flashing should also be checked with care. To fasten down a loose shingle, lift it gently and apply a plastic roofing cement underneath it.
Small cracks should be repaired with roofing cement. Trowel it into the cracks; if you make any smears, dip a cloth in solvent and wipe them up.
Torn or split shingles should be patched with roofing cement and secured with roofing nails.
Badly damaged shingles should be replaced. Loosen nails in the shingle above the damaged one by slipping a flat shovel underneath (see Diagram 1). Then pull the nails and remove the bad shingle.
After measuring for a snug fit, cut a new piece and slip it into place under the shingle above (see Diagram 2). Align with adjacent shingles.
Try to drive new nails through the holes left by the old ones. If you can't, carefully seal the old openings with roofing cement (see Diagram 3).
Now coat the nailheads with roofing cement (see Diagram 4), then press the upper course firmly back into place. Weight it down, if necessary.
If you don't have any replacement shingles, you can use a piece of metal flashing to reinforce a badly damaged shingle (see Diagram 5). Cut a piece a bit smaller than the shingle, slip the metal underneath the shingle, and nail the metal to the roof. Then coat the underside of the damaged shingle with roofing cement and press the shingle back in place.
Loose shingles should be nailed down securely. If a shingle has a minor split, slide roofing paper or sheet aluminum cut to the size of the shingle under the crack, drill pilot holes along the split, then nail along both edges. Seal the split with roofing cement.
Warped shingles should be split carefully at the warp with a hammer and chisel, then handled as above.
Moss growing on shingles can cause the wood to decay. Scrape moss off with a stiff-bristled wire brush and treat the roof with wood preservative.
Shingles that have broken edges, severe splits, or extensive decay should be replaced. Remove the shingle by splitting it along the grain with a hammer and chisel, then use a hacksaw to cut out nails under the course above. Drive the new shingle into place, using a hammer and wooden block. Leave a 1/4-inch space at either side of the new shingle to accommodate swelling. Finally, drive a couple of galvanized roofing nails just below the lap line for the course above and seal with roofing cement.