Synthetic vs. Felt Roofing Underlayment: Which To Choose

When you think about roofs, you typically think shingles or metal roofing. But what you may not know is there’s a layer of protection right on top of the roof deck itself, and under the actual roof that plays an important role in protecting your house from moisture damage. It’s called roofing underlayment.

Let’s dig in and find out more about this important component of your roof’s structure.

What Is Roofing Underlayment?

Roofing underlayment is the layer that lies between the roof covering and the roof deck, which is typically plywood or OSB. It is installed directly on top of the roof deck, and provides an extra layer of protection from the elements.

Types of Roofing Underlayment

There are two leading types of roof underlayment product: felt and synthetic.

Each type has pros and cons, and the one you (or your roofer) choose may depend on the area you live in, roofing materials used, the roof design, and total budget

Felt Roofing Underlayment

Felt roofing underlayment is a long-time standard. It is created by using asphalt to saturate paper or fiberglass mat.

Felt underlayment is usually available in two types: No.15 felt and No. 30 felt. Compared to No. 15 felt, No. 30 felt is thicker & stronger, and less prone to tearing or ripping off during installation or extreme weather.

Felt Underlayment Pros

The biggest advantage of using felt roofing underlayment is cost. Felt tends to cost less than synthetic underlayment, which is why it’s almost always the go-to for budget-minded home owners.

Felt Underlayment Cons

There are some disadvantages to using felt roof underlayment, however. One is that it typically can’t be left exposed for more than a few hours. The material can dry out or discharge oils in the heat. This can greatly impact the felt’s ability to block out moisture.

Other drawbacks of felt roofing underlayment include:

Tearing in high winds and/or during installation.
If exposed to moisture, it can absorb water and wrinkle, making it difficult for shingles to lay flat.
Felt underlayment weighs more than synthetic, which can prove difficult for roofing contractors to drag rolls up a ladder.
It has a slick surface, which can also make it difficult to install.
The weight also means less material per roll. Thus, more possible seams instead of a single run with no laps.

Synthetic Roofing Underlayment

For extra water-resistance and protection from weather, many roofing contractors are choosing synthetic roof underlayment. These products are normally made from polymers, which deliver additional strength and longevity. This underlay is usually moisture-resistant, and when installed by professionals, offers substantially better protection from the elements, when compared to felt.

However, these materials are not standardized. Different manufacturers may construct their products differently, and may have different levels of performance. Be sure to do some research and speak with a reputable roofing company that can help you in selecting the right roof materials for your home.

Synthetic Underlayment Pros

There are four prime benefits of installing synthetic roof underlay over felt. Compared to felt underlayment, the synthetic option is:

Tough
Fast to install
Safe
Water repellant

Synthetic roofing underlayment is significantly durable. It normally does not tear/rip and is advisable for extended UV and water exposure. This is super helpful if there will be some lead time before the final roof covering is installed.

Synthetic roofing underlayment is also typically:

Up to four times lighter
In wider and longer rolls, which results in fewer trips up the ladder for the roofers, saving time and moving the job more quickly.
Safer for the roofing contractor. The surface of these underlayments almost always feature a slip-resistant surface for better walkability. It’s also marked with overlap guides and fastener indicators, which helps to improve consistency and accuracy when installing.
Built to repel water. This is important for moisture infiltration, especially if the underlayment is or will be exposed for a long period of time.

Since it is made of plastic, synthetic roofing underlayment is usually resistant to mold development, a decisive advantage over felt.

Synthetic Underlayment Cons

While synthetics are competitively priced, the largest drawback is cost. The initial investment on high quality roof materials could save you money in the long run, however. It’s hard to put a price on peace of mind when it comes to protecting your home from moisture.

The Right Underlayment for Your Roof

Whether it’s time for a re-roof or new home construction, there are many factors to consider when deciding which type of underlayment to use. Synthetic roofing underlayment has several advantages over felt and is likely a worthwhile investment. When you need to protect your roof and home from the risks of water and moisture infiltration, call the East Texas roofing experts at C&S.