You can usually nail down a warped or loose shingle, but if a shingle is broken or missing, you’ll need to replace it. Here’s how:

1) Pull out the broken pieces.

2) Pry out the nails that held the shingle in place (these are located under the next course up the wall). The easiest tool for doing this is a flat bar, but sometimes it’s easier to cut the nails off with a hacksaw blade.

3) Cut a replacement shingle to the proper width; allow about 1/4 inch of clearance between this shingle and its two neighbors to allow for expansion.

4) Place the shingle in position, leaving its butt about 3/8 inch below the butt line of the adjacent shingles; nail it with two shingle nails, spaced about 1 inch in from the sides and just beneath the butts of the shingles above. Once you are done nailing, drive the shingle upward the last 3/8 inch to hide the nailheads.

5) To blend the shingle with the grayed tones of aged shingles, brush on a mixture of baking soda and water.