Mineral-surfaced asphalt shingles are made in strips of two, three, or four units or tabs joined together, as well as in the form of individual shingles. When laid, strip shingles furnish practically the same patterns as individual shingles, and both strip and individual types are available in different shapes and sizes.
The principal damage to asphalt-shingle roofs is caused by the action of strong winds on shingles which have been nailed too close to the upper edge of the shingle. The tabs or individual shingles most likely to be affected by winds are those in the four or five courses near the ridge or in the area extending about 5 feet from the sloping edge or rake of the roof.
To fasten the loose shingles securely, use a putty knife or trowel to place a small quantity of flashing cement under the center of each tab or shingle about 1 inch above the lower edge and press down firmly. Too much cement will prevent the tab or shingle from lying flat. Do not seal the lower edge completely.
Asphalt shingles are frequently applied over old wood shingles or other roofing provided the surface of the old covering is in reasonably good condition. If not, it should be removed. For a shingled roof, where the deck has not been laid solid there will be open spaces between the wood strips to which the old shingles are nailed. The exact location of these strips should be marked so that the nails used to fasten the new roofing will encounter solid wood.
All defective or missing shingles should be replaced and beveled strips, 2 by 4 inches or the same thickness as the butts of old wood shingles, should be nailed at the base of the shingles to make the surface uniform.