What is the top lap of a shingle typically designed to be?

The top lap of a shingle is typically designed to be about 3 inches. This measurement is critical for ensuring proper water drainage and minimizing the risk of water penetration under the shingles. A 3-inch lap means that a significant portion of the lower shingle is covered by the upper shingle, which creates a more effective barrier against the elements.

This standard lap also helps to align the shingles in a way that maintains a uniform appearance and adequately supports the weight of the shingles above. Additionally, a 3-inch overlap allows for the mechanical fastening of the shingles to achieve stability, especially in areas prone to high winds.

Therefore, the design choice of a 3-inch top lap reflects the industry's guidelines for optimal performance and durability of the roofing system, enhancing its resistance to leaks and weathering over time.