Is an underlayment required under all asphalt shingles?

An underlayment is indeed required under all asphalt shingles as it serves several critical functions. It acts as a secondary barrier against water infiltration, protecting the roof deck from moisture that may penetrate the shingles due to wind-driven rain or other factors. This is especially important since asphalt shingles, while generally effective, can be susceptible to leaks over time, particularly in areas where there may be high wind or snow accumulation.

Furthermore, underlayment provides an additional layer of insulation and can help prevent the shingles from sticking to the roof deck, which can be beneficial in prolonging the lifespan of the roofing material. Additionally, it can enhance the roof's fire resistance, improving the overall safety of the structure. Because of these reasons, building codes and manufacturers typically require this installation regardless of climate or roof pitch, making it an essential part of roofing systems using asphalt shingles.