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Getting started on an asphalt shingle roof
Before you attach your first shingle, make sure you begin with the proper underlayment and roof edging. They're critical elements for a waterproof roof.
After you've obtained a permit (if needed) and safely stripped the roof clean, nail drip edge flashing flush along the eave.
Windblown heavy rain and/or snow can force water up and under even properly installed shingles. Even worse are ice dams (frozen water/snow that builds up on roof edges), which can wreak havoc by allowing water to seep up under lower shingles and then drip into your house. To guard against such seepage, apply self-adhesive waterproof underlayment (“ice barrier”), which adheres tightly to bare roof sheathing and seals around nails driven through it. Buy it at roofing supply companies or home centers. In severe climate regions, most building codes require applying it 3 to 6 ft. up from the eave (minimum of 2 ft. past the exterior wall). Call your building inspector for local details.
Cover the rest of the roof with No. 15 asphalt-saturated felt underlayment (some codes may require No. 30). Each layer overlaps the lower one by at least 2 in. Follow this step by nailing drip edge along rakes (sides of roof), on top of the underlayment. As you did with the flashing, always lap upper pieces over lower pieces. The felt keeps the roof deck dry before shingles go on, protects against wind-driven rain as shingles fail and increases fire resistance.
Next, find the center of the roof at the top and the eave, then snap a vertical chalk line. Most pros use this line to begin shingling, working left and right toward the rakes. Shingle manufacturers may recommend starting at the left rake edge, so check package recommendations.
For the first row of shingles, called a starter course or strip, you cut the tabs off three-tab shingles and apply them with the self-sealing adhesive strip facing up along the eave. Make sure this row has a slight overhang (1/4 to 3/8 in.) beyond the drip edge. The starter course protects the roof by filling in the spaces under the cutouts and joints of the next row (first course) of shingles. The adhesive on the starter course seals the tabs of the first full course.
Finally, nail the first course of shingles directly on top of and flush with the starter course. Use four roofing nails per shingle, as indicated on package instructions (six nails in high-wind areas). Once this course is laid, you can begin snapping horizontal chalk lines up the roof to ensure straight rows. Make sure to expose 5 in. of the shingle tabs where the bottom edge of the tab meets the top of the cutout.
Asphalt Shingle Roof
Snap a chalk line at the center of the roof as a starting point. Cut the tabs off the first course of shingles, then overhang the shingle slightly.