The Benefits & Drawbacks Of Felt Underlayment And Synthetic Underlayment

Posted on: 7 January 2021


When it comes to building a roof, there are three important layers: the decking, the underlayment, and the shingles. The decking is the plywood that forms the base of your roof. The underlayment is the protective layer that acts as a barrier between the shingles and the decking. The shingles are the exposed portion of your roof that has to be able to withstand years of environmental exposure and wear.

When it comes to underlayments, there are two primary categories: felt underlayment and synthetic underlayment. These two different types of underlayment are the most common ones used on residential projects.

Felt Underlayment

Felt underlayment is often used with asphalt shingles. It is designed to be thick and heavy, although some types of felt underlayment are not as strong as synthetic underlayment. 

Once felt underlayment is placed on a roof, it should be covered up with shingles immediately. When it is left exposed for a while, it tends to be less weather resistant, so a felt underlayment should not be placed on a roof unless shingles will be immediately installed next. It shouldn't be exposed to wind or rain before it is covered up.

Over time, felt underlayment tends to wrinkle up and can be prone to water absorption after years of usage.

Felt is easy to work with and is not that labor-intensive to install. It can act as a solid barrier between your decking and your shingles.

Synthetic Underlayment

Synthetic underlayment is a newer material than felt underlayment. It tends to cost more than felt underlayment, depending upon the grade of synthetic material you choose for your roof.

Synthetic underlayment is light and easy to move around; it is not more cumbersome than felt to work with. It doesn't wrinkle as easily over time, and it is not likely to rot because it doesn't contain organic material. It provides extended protection and is great for low-pitched roofs where rain and ice could get under the shingles.

Synthetic underlayment can withstand exposure to the elements, so if you need to put down the underlayment and then lay down shingles later, you can do so.

The two most common types of underlayment materials for residential roofs are felt underlayment and synthetic underlayment. Felt underlayment is a more traditional material and is relatively affordable; however, it can break down more easily over time due to the organic materials used in the product. Synthetic underlayment is more expensive and can withstand environmental exposure. Talk to your roofing professional to determine what type of underlayment will work best for your new roof installation project.