Figure 3-33. Butt shingle
3-17. Shingle Installation. The first step in covering a roof is to erect a scaffold to a height that will
bring the eaves about waist-high to a man standing on the scaffold. Before any roof covering is applied,
the roof sheathing must be swept clean and carefully inspected for irregularities, cracks, holes, or other
defects. No roof should be applied unless the sheathing boards are absolutely dry. An underlay of
roofing felt is first applied to the sheathing. Roofing felt usually comes in 3-foot-wide rolls and should
be laid with a 2-inch top lap and a 4-inch side lap (see Figure 3-34). Bundles of shingles should be
distributed along the scaffold before work begins. There are 27 strips in a bundle of 1 by 3 asphalt strip
shingles. Three bundles will cover 100 square feet.
Figure 3-34. Laying an asphalt shingle roof
a. Install the first course of shingles inverted.
This arrangement provides a roofing edge
b. Nail inverted shingles in place with 3/4-inch over the drip edge on the eaves and the gable
ends of the roof (see Figure 3-35, page 3-28).