a. Square. Roofing is estimated and sold by the square. A square is the number of shingles required to cover 100 square feet of roof surfaces.

b. Coverage. Shingles overlap, and depending on the manner in which they are laid, one, two, or three thicknesses cover the roof at any one place. The roofing is termed single coverage, double coverage, and so on.

c. Shingle Butt. The shingle butt is the lower exposed edge of the shingle.

d. Exposure. The exposure is the distance from the butt of one shingle to the butt of the shingle above it. This is the portion of the shingle that is exposed to the weather.

e. Underlayment. The underlayment is the application of saturated felt that is placed over the roof surface to protect the roof sheathing until the shingles are applied.

f. Toplap. The width of the shingles minus the exposure.