What is the purpose of the head lap in roofing?

The purpose of the head lap in roofing is to provide additional overlap of shingles, enhancing weather resistance. This overlapping is essential because it helps to direct water away from the seams and joints of the roofing material, reducing the likelihood of leaks and water penetration. Proper head lap ensures that each row of shingles covers the seam of the row beneath it, creating a barrier against wind-driven rain and other adverse weather conditions.

When shingles are installed with the correct amount of head lap, it also helps to improve the overall durability of the roof, as it minimizes the risk of water accumulation underneath the shingles that could lead to rot or other forms of degradation. Thus, the correct choice emphasizes the practical aspect of roofing design, ensuring that the roof remains effective in protecting the structure beneath it.