Most jurisdictions allow how many layers of shingles to be applied to a roof?

Many jurisdictions permit a maximum of two layers of asphalt shingles to be installed on a roof. This regulation is primarily based on considerations related to the weight of the roofing system, which can affect the structural integrity of the building. Adding too many layers may exceed the design limits of the roof structure, potentially causing sagging or failure over time.

Furthermore, when installing a second layer of shingles, it's essential to ensure that the underlying layer is in good condition and securely fastened, as any damage or loose shingles can compromise the effectiveness of the new layer. Building codes are designed to maintain safety and performance standards, which is why the two-layer limit is commonly enforced across many areas. This restriction helps ensure that roofs can adequately shed water and withstand the elements while also being manageable in terms of maintenance and repair.