Before laying asphalt shingles the rafters should be covered with tongued and grooved roofing-boards, and these covered with black waterproof building-paper, lapped 2 inches.
There are two types of asphalt shingle units. One consists of a unit of twin shingles, so arranged that the butt ends which show to the weather appear as two individual shingles, and the other consists of one shingle unit. Both types are usually laid 4 inches to the weather and nailed with 1-inch galvanized nails No. 10 wire with 3/8-inch heads. At the eaves should be nailed a galvanized-metal drip edge, and over this a double course of shingles for the first course. Hips and ridges are finished with what appears to be a Boston hip, but the shingles are bent over the hip line. The valleys and gutters are best when they are lined with strips of ready roofing similar to the shingles themselves.
Asphalt shingles which come in long rolls or units of four or five are laid in a similar manner, except that, due to their continuous length, they are unable to expand without bulging up on the roof.