Wind, rain, sleet, hail, snow and the hot summer sun . . . Considering all your roof has to withstand, it's a wonder the shingles have a life of 15 to 30 years.
Still, now and then a shingle gives out: It may dry out with age and crack when flexed by a heavy wind. Or a branch might fall on it, punching a hole or breaking off a tab. So it pays to inspect your roof periodically.
No need to climb up there, however. In fact, it's best to stay off your roof. Foot traffic is just one more form of abuse your roof can do without. So, two or three times a year, and after any heavy storm, take binoculars out in the yard and give your roof a careful scan. Look for cracks, curled shingles, broken shingles, missing tabs, anything out of the ordinary.
If you spot trouble, try to fix it the first warm day that comes along - a warm roof is more pliable, shingles are less likely to crack and cements handle and stick better.
Wear rubber-soled shoes. The best are high-topped sneakers, which combine traction with good ankle support.
Curled shingles are easiest to repair. Simply load a caulking gun with a cartridge of shingle cement, squirt a bead of the sticky stuff under any lifted or curled tabs and press them down into the cement.
Cracks and tears are almost as easy. You can fix a cracked shingle with roofing cement. Trowel some under the crack if you can, but if the shingle is stuck down and brittle, forget about putting cement under it. In any case, do trowel a coat of cement over and into the crack with a putty knife.
If the shingle is torn, you'll be able to trowel cement under the tear. Then nail along both edges of the tear with one-inch galvanized roofing nails. Finally, put a coat of cement over the tear and the nailheads.
If a shingle is badly damaged, it's best to replace it. Carefully raise the tabs of the shingles in the row directly above the damage one. Slip a thin pry-bar under those raised tabs and pull any nails you see holding the damaged shingle in place. Then try to pull the damaged shingle free.
It may still be held in place by a second row of nails (under the shingles two rows up the roof), but never mind. You should be able to pull the shingle free anyway; that other row of nails is very close to the edge of the shingle, so it will tear free.
Save that shingle! If indeed you did have to tear it free you can use it as a pattern to cut notches in the edge of the replacement shingle. These notches will go where the second row of nails would pass through.
Slip the new shingle into place. Raise the flaps of the shingles above the new shingle and nail it in place. Put one nail at each edge of the new shingle, and one about 3/4 inch above each of the tabs cutouts. Cement the tabs of the new shingle in place.