When most people think of roofing, they picture shingles and gutters. Many people are unaware that an additional layer of defense plays a crucial role in preventing moisture damage to your home and is located immediately between the shingle layer and your roof deck. It is known as roofing underlayment and is an essential part of your roofing system. Let’s find out more about this critical component of your roof.

How Does Roofing Underlayment Work and What Is It?

The material layer under your roof’s shingle layer is known as the roofing underlayment. It’s a secondary layer built right on top of the roof deck, designed to keep moisture from penetrating the wooden layer of your roof and provide protection from wind, rain, and snow.

Various Roofing Underlayment Types

Felt and synthetic are the two main categories of roofing underlayment. Each has benefits and drawbacks, and the type you select may be influenced by your location, the roofing materials you use, the design of your roof, your budget, and your roofing contractor.

Felt Underlayment for Roofing

One of the original varieties of roofing underlayment is felt. It is made by soaking fiberglass mats or paper in asphalt. There are typically two felt roofing underlayments: No. 15 felt and No. 30 felt. No. 30 felt is frequently thicker, stronger, and potentially less prone to tearing or ripping off during installation or weather events than No. 15 felt.


 Cost is the primary benefit of utilizing felt as roofing underlayment. Homeowners frequently choose felt underlayment on a tight budget since it is typically less expensive than synthetic underlayment.


Felt underlayment has several drawbacks when used on a roof. Traditional felt roofing underlayment has the drawback of typically not being able to be left exposed for longer than a few hours. The heat could cause the material to dry out or leach oils. This would affect the felt’s capacity to repel moisture.

Among felt underlayment’s further downsides are:

It is prone to tearing during installation and in strong gusts. It becomes challenging for the shingles to sit flat when the mat is exposed to moisture since water absorbs it and wrinkles the felt. As soon as the felt roofing underlayment is placed, shingles should be installed to provide optimum protection.

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Due to its weight, felt underlayment is more challenging for roofing contractors to carry in rolls up a ladder and onto a roof. It also has a slippery surface, occasionally making installation more difficult. There is less material per roll due to weight. This increases the number of potential seams rather than having a single circuit with no laps.

Synthetic Underlayment for Roofing

Synthetic roofing underlayment is popular among roofers because it offers better weather and water resistance. The strength and durability of these things are improved by using durable polymers in their construction. When correctly installed, this underlayment offers better weather protection than felt and is typically moisture-resistant.

Due to the non-standardization of synthetic roofing underlayment materials, different manufacturers may make their goods with differing performance levels. Make sure to conduct your research and speak with a reliable contractor who can help you select the appropriate roofing materials for your home.


There are four main benefits of using synthetic roof underlayment instead of felt. The following benefits of synthetic roofing underlayment over felt:

  • Tough
  • rapid installation
  • Safe
  • water repels
  • Compared to felt, synthetic underlayment has an incredibly high tear strength and a robust, long-lasting composition.

Underlayment for synthetic roofs is incredibly robust. When there is some lead time before your roof covering is placed, it is especially advantageous because it generally doesn’t tear and is sometimes acceptable for prolonged UV and moisture exposure.

The ability of synthetic underlayment to endure boot action is crucial when your roofing contractor is installing it. At Owens Corning Roofing, we refer to this as “use after abuse” since the product might still function as intended even after the damage it experiences during installation. In some circumstances, synthetic roofing underlayment can be up to four times lighter than felt.

Fast installation: Because synthetic roofing underlayment comes in broader and longer rolls with more material per roll than felt, your roofers will have to climb the ladder fewer times, saving time and speeding up the job. For instance, it might take three rolls of synthetic underlayment to cover a typical 2700-square-foot home, but it might take 14 rolls of No. 30 felt to do the same.

Safe – Many synthetic roofing underlayments, including those sold by Owens Corning, have surfaces with various slip-resistant textures for easier walking. Indicators of where fasteners should go and overlap guides are typically neatly indicated, which aids in consistency and accuracy during installation.

Moisture Resistant: Felt products absorb moisture, but synthetic roofing underlayments are made to reject it. This is important for homeowners who are worried about water getting in, especially if the underlayment will be out in the open for a long time. Unlike felt, synthetic underlayment frequently resists mold formation since it is made of plastic.


The major drawback of synthetic roofing underlayment, even though many of them are competitively priced, is how expensive it is compared to felt. But spending more on better roofing materials up front can save you money in the long run. The peace of mind that comes from knowing your roof is well-protected against moisture cannot be overstated.

Roof Underlayment That Is Right for You

When replacing a roof or building a new home, there are a few things to think about when choosing the underlayment. Synthetic roofing underlayment is better than felt in many ways when it comes to keeping water and moisture out of your roof and house.

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