Understanding underlayment

By Emma Peterson. 

Learn about the two main categories of underlayment and where they should be used on your roof. 

Underlayment is a crucial part of your roof, but too often it flies under the radar. In this AskARoofer Podcast, Alice Reynolds and Megan Ellsworth spoke with Dominic Favazza from GCP to understand the importance of this part of the roof system. Dominic has been in the industry for over 12 years, working both on commercial roofs and residential. He explained the basics of underlayment, saying, “In its simplest form, underlayment is what lies between the shingles and the roof deck." It acts as an extra barrier between the roof deck, which is typically made of OSB or plywood, to help protect from the elements.  

Overall, there are two types of underlayment, mechanically fastened and self-adhering. Mechanically fastened underlayments are most typically found in the form of synthetics, tar paper or felt paper. As for self-adhered, it is specifically designed for optimum waterproofing and durability. Dominic explained, “Self-adheres are typically going to be associated with what we would consider high stress areas. So, your eaves, your valleys, your rakes, up to your warm wall.”  

A key part of understanding underlayments is that you don’t have to choose just one! Dominic elaborated, “You can go from an ice and water shield, which is going to be a self-adhered membrane, around the edge of the roof to the middle of that with a synthetic rolled out and mechanically fastened underling.” When it comes to choosing your type of underlayment, or combination of types, your area’s weather concerns and building codes are big factors; as are your budget constraints and your home’s structural design. Dominic summed it up by saying, “Try to think about your roof as not just the shingles, but as a system. And that system’s needs differ depending on where you live.” 

Read the transcript or Listen to the podcast to learn more about choosing and maintaining the right underlayment for your roof!