How to replace damaged shingles
1. When a three-tab asphalt shingle was installed, four nails should have been hammered along its midline, just above the tab cutouts. Another four nails, hammered through the row above, secure the top of the shingle. Removing and replacing a damaged shingle requires removing its nails and the nails one row up.
2. Slip a cat's paw, or small prybar, under the damaged shingle to loosen nails (protect the shingle below with a scrap of wood), then wiggle them out. Similarly, loosen the nails on the row above. You won't need to remove these completely, just enough to slide the damaged shingle out.
3. Trim the new shingle to match the size of the old and slide it into place.
4. Re-nail the shingle. To avoid leaks, try to get new nails into the old holes. If this is difficult, first seal the old holes with roofing cement. Since the nail heads are hidden under shingles, use scrap wood as a nailing block so as not to damage those shingles.
5. Cover the nail heads with a dab of roofing cement. Another dab will help hold the corners of each tab down. If needed, weight the shingles down overnight, but be sure that the weight won't slide off and injure anyone.
Roofer's checklist
1. Vents, plumbing stacks and similar roof penetrations use purpose-made flashings combining rubber or neoprene sleeves and metal. The top and sides sit under the shingles, the bottom sits on top
2. There are several ways to shingle the seam between two sloped fields of the roof. Valleys can be open, as shown here, with a continuous strip of flashing underneath the trimmed shingles. Or valleys can be closed, so the shingles from each side of the valley are interwoven-an approach that requires more skill but experts argue is superior
3. Chimneys require a complex system of overlapping step flashing. Two keys to a long-lasting seal: the top edges must be mortared into the brick joint, and the back of the chimney (not shown) needs a cricket to divert water from very vulnerable roof seams
4. Another drip edge protects the fascia board and diverts water into the eavestroughs. This one should sit under the underlay
5. Where roof meets gable wall, the roofing underlay is folded to run at least 4" up the wall. On top of that, step flashing is woven in with the shingles. Finally, siding is installed on the wall and hides the leak-resistant seam beneath
6. A drip edge along the rake of a gabled roof is an often-missed detail, but it helps protect the rake board. It should sit above any underlay
Read more in Home Reno & Design and Outdoor
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