For new installations or replacement installations where existing shingles are removed down to the roof sheathing, the roof is prepared for shingles by installing building paper (or tar paper) over the sheathing and metal drip edges along the perimeter of the roof, if not present. Most asphalt shingles come in a standard 12-inch x 36-inch, three-tab configuration, and are purchased in squares, packages containing enough shingles to cover 100 square feet. The number of squares needed is determined by dividing the square footage of the roof by 100.
In addition to the asphalt shingles, a ladder, chalk line, utility knife, straightedge, hammer and 1-1/2 inch galvanized roofing nails are needed for the installation of asphalt shingles.
Installation of asphalt shingles begins with a starter course. A straight chalk line is snapped 11-1/2 inches up from the leading edge of the metal drip edge, which will allow one-half inch overhang. Six inches are cut off one shingle, which is used to start the first course at a gable end. The shingle is positioned upside-down, overhanging the gable end by 1/2 inch with the shingle tabs positioned on the chalk line. The shingle is secured with four roofing nails driven about 3-1/2 inches up from the bottom edge until nail heads are flush with the surface of the shingle. Full shingles are used for the remainder of the starter course, positioned upside-down, tabs on the chalk line and edges butted together. Each shingle is attached with four evenly spaced roofing nails. Any excess at the end of the completed first course is trimmed off, leaving a one-half inch overhang at the gable edge.
A first course is installed over the completed starter course. Starting at the same gable edge as before, a full shingle is installed right-side-up with tab down, aligned with the edge of the starter course. The remainder of the course is installed in the same manner, with edges butted together. Shingles that make up the first and subsequent courses are secured with four roofing nails, one about 1/2 inch above each tab and at the ends about one inch in from each edge. The last shingle is trimmed to match the starter course.
Beginning with the second course, a chalk line is snapped 17 inches up from the bottom edge of the preceding course to provide a 5-inch exposure for each course. Full shingles are used to start each subsequent course, but a portion of the shingle is positioned to overhang the gable: one-half tab for the second course, a full tab for the third course and
1-1/2 tabs for the fourth course. A full shingle aligned with the first course is used to start the fifth course. This pattern is repeated for any subsequent courses and is necessary to develop the familiar staggered pattern seen on asphalt shingle roofs. Once the entire roof has been shingled, the gable ends are trimmed to produce a uniform one-half inch overhang.
Once the entire roof has been shingled from the eaves to the roof ridge, ridge caps are installed to complete the installation. Ridge caps are made by cutting full shingles from the notch in the tabs to the edge, providing three ridge caps from each shingle. One ridge cap is needed for every five inches of ridge. Ridge caps are installed by bending them into place over the ridge and fastening them with one roofing nail on each side of the ridge. The nails in the last ridge cap are exposed and are generally covered with roofing cement to avoid leaks.
Installation of asphalt shingles requires working at heights on the roof. Care must be taken to avoid dangerous falls.