As it’s name implies, a roof underlayment is the material that is applied to the roof deck prior to the installation of shingles or other roof materials. It takes more than just shingles to protect your roof. It takes an integrated system of components and layers designed to withstand the forces of nature outside while controlling temperature and humidity inside.
Underlayment plays a critical role in protecting from water in filtration from the freeze/thaw cycle and wind-driven rain and water flow around chimneys, vents, eaves valleys and skylights.
Traditionally, roofing felt infused with asphalt or fiberglass was used as the primary underlayment for most residential roofs. However, synthetic roof underlayment are gaining in popularity on the mountain environment. Synthetic underlayment offers superior moisture resistance and longevity.