Underlayment is the last line of defense for a roof to withstand the elements and helps protect a home's interior. It’s a water-resistant membrane and is the first component to be installed on a roof deck.
For decades, asphalt-saturated felt was the most common underlayment used on steep-slope residential roofs and continues to be the industry standard. However, innovative roofing technology has helped produce engineered underlayment, which offers additional protection for a roof compared to traditional felt.