The answer to 'how long does underlayment last' is that the lifespan of roofing underlayment can vary greatly, but it typically lasts between 10-20 years when properly installed. Underlayment is the protective layer installed between the roof deck and the shingles or other roofing material. Its main purpose is to provide a secondary barrier against water penetration and to protect the roof deck from the elements.
The exact lifespan of underlayment depends on factors such as the type of material (asphalt-based, synthetic, or rubberized), the quality of the installation, and the climate and weather conditions the roof is exposed to. In general, higher-quality underlayment materials tend to last longer than lower-quality options. Proper installation is also crucial, as any gaps or tears in the underlayment can significantly reduce its effectiveness and lifespan.