Roof Underlayment Guide

Roof Underlayment Guide

4 August 2021
 Categories: , Blog

There are several components that make up a new roof. You are likely prepared to choose your shingle type and color, but you may be unaware of components like underlayment and the several different choices for it. The following guide can help you better understand underlayment and your roof. 


Underlayment is a membrane layer that goes on over the top of the roof cladding but under the shingles. It is used with all shingle types, from asphalt and tile shingles to metal panel roofs. 

Its main purpose is to provide a second layer of protection over the roof. Roof cladding is typically made of plywood or OSB wood, both of which can suffer moisture damage if any water gets beneath the shingles. Underlayment can guard against minor moisture incursions, such as from driving rain or a temporarily damaged shingle. Although you can't see the underlayment, it is an important protective component of your roof.


There are two main types of underlayment, felt and synthetic. Felt, also called tar paper, was mainly used in the past. It consists of a roofing paper or fiberglass mat that has been impregnated with asphalt. It's a more budget-friendly underlayment option, but felt does have several drawbacks. It's more prone to tearing and moisture damage, has more seams after installation, and can add quite a bit of weight to the roof.

Synthetic is the modern-day industry standard. Although the material varies by manufacturer, synthetic is generally a polymer-based material that provides superior waterproofing ability. It doesn't tear easily, and the larger rolls result in fewer seams and a quicker installation. Synthetic underlayment is also very lightweight, so it can be used under heavier roofing materials like tile without adding too much additional weight to the roof. 


In nearly all cases, synthetic underlayment is the ideal choice for a new roof. It is long-lasting, lighter weight, and more effective than felt. It is recommended by most roofing contractors, as well as many shingle manufacturers, and synthetic may be required by the manufacturers for warranty purposes. 

Felt is no longer in common use by professional roofers, and it's typically only used for small DIY jobs such as shed roofing. The only real benefit of felt compared to synthetic is that felt underlayment typically costs less.

Contact a roofing service in your area if you have questions about the underlayment or other roofing component options that are available.