Which statement correctly defines head lap in standard shingle practice?

• A. The shortest distance from the butt edge of an overlapping shingle to the upper edge of the shingle two courses below it.
• B. The distance from the butt edge of a shingle to the top edge of the same shingle in the next course.
• C. The entire upper portion of a shingle covered by the succeeding course after installation.
• D. The minimum overlap required by code to prevent leaks.

Answer: (B)

Headlap is the vertical overlap between successive shingle courses. It is defined as the distance from the butt edge of a shingle to the top edge of the same shingle in the next course above it. This spacing ensures the shingle in the higher course covers the nails and the seam of the lower course, providing weatherproofing and a consistent appearance. The other descriptions don’t match this specific measurement: one describes overlap to a shingle several courses away, another describes the entire portion covered rather than a measured distance, and another refers to a code minimum rather than how headlap is defined.