What is the function of head lap in shingle installation?

Head lap is critical in shingle installation as it ensures proper overlap of the shingles along the roof's slope. This overlap helps to create a water-resistant barrier, directing rainwater down the roof and preventing it from seeping underneath the shingles. Proper head lap also helps maintain the architectural appearance of the roof by ensuring that shingles are aligned correctly, thus preventing any gaps that could lead to leaks or water intrusion. This feature is essential for the longevity and performance of the roofing system.

While other aspects of shingle installation contribute to overall stability and aesthetics, only the head lap specifically addresses the need for overlapping shingle courses to provide effective waterproofing.