Asphalt-Saturated Felt Underlayment: A Complete Guide

Asphalt-Saturated Felt Underlayment: A Complete Guide

The roof is an integral part of every home as it protects you from elements like sunlight, rain, and potential hazards during storms. If you once hired a roofing company for a roof replacement or maintenance, you have likely heard about and discussed roofing underlayment. If you haven’t, take time to know what it is and what it does for your roof—it’s crucial for every roofing system, after all!

The primary barrier of your roof is the shingles. They do well to block rain and snow and absorb the sun’s strong rays. However, they don’t cover every single millimeter of space on your roof. Shingles can also be torn away from your roof by a strong wind, and you need a second layer of defense underneath to keep your interiors safe and dry.

In a nutshell, a roofing underlayment is material placed on a roof deck. This underlayment provides an extra layer of protection against elements like rain and snow. Different materials can be used for roof underlayment: rubberized asphalt, non-bitumen synthetic, and asphalt-saturated felt.


In this article, we will take a close look at asphalt-saturated felt underlayment: what it is, its advantages and disadvantages, and how it fares compared to other underlayment types.

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What is Asphalt-Saturated Felt Underlayment?

Asphalt-saturated felt is the oldest and most popular underlayment type that roofing professionals have been using for decades. It is made from organic or fiberglass substrate. The felt is saturated in crude oil byproducts to make the paper firm enough to be water-resistant.

This underlayment is installed in many residential roofing systems. Despite being water-resistant, asphalt-saturated felt is not entirely waterproof.

Asphalt-saturated felt is available in two thicknesses: 15 pounds and 30 pounds. The 30-pound felt is the better choice between the two thicknesses as it is more resistant to any form of damage during installation. It can also protect the roof longer since it is stiffer and thicker.

For many years, asphalt-saturated felt has been the top choice among roofers and architects since it is cost-effective and easy to install. Local building codes also approved the use of felt as roof underlayment.

Pros and Cons of Installing Asphalt-Saturated Felt Underlayment

Using asphalt-saturated felt as your roofing underlayment can bring both advantages and drawbacks. Here are some of them:

Pros of Asphalt-Saturated Felt

  • Asphalt is the cheapest option among all underlayment types. 
  • High-quality asphalt felt provides an excellent seepage barrier, protecting roofing systems from roof leaks
  • Using an ASTM D226 and ASTM D4869-compliant underlayment offers better protection in terms of water absorption.

Cons of Asphalt-Saturated Felt

  • Low-quality asphalt material can be easily torn and damaged during installation.
  • Asphalt felt is made of volatile compounds. Sunlight exposure will damage the felt easily since the compounds fade, making the felt more susceptible to water absorption and more fragile.

Asphalt-Saturated Felt Underlayment vs. Synthetic Underlayment: Which is Better?

Here are some ways asphalt felt underlayment is better than synthetic underlayment:

  • Asphalt felt is cheaper than other synthetic materials. Today, 30-pound felt costs 10 cents for every square foot. A vapor impermeable synthetic underlayment ranges from 11 to 15 cents per square foot, while the vapor-permeable synthetic underlayment costs 20 to 90 cents per square foot.
  • Asphalt felt is more durable than synthetic underlayment in terms of water absorption. Hence, synthetic underlayment is more likely to cause moisture damage to the roof over time.
  • Asphalt underlayment provides more water-barrier properties than synthetic underlayment.
  • When installing asphalt felt underlayment, you only need basic installation tools like roofing nails or staples.

In contrast, here are the ways synthetic underlayment is more advantageous than asphalt-saturated felt underlayment:

  • Synthetic underlayment, being made of lightweight material, is easier to install compared to asphalt felt. 
  • Synthetic underlayment becomes much more effective in terms of the water barrier property in terms of the pure density of the material. Hence, roofs with synthetic underlayment have less weight when soaked in rainwater.
  • If asphalt’s best quality is seepage barrier, synthetic underlayment’s most significant advantage is sturdiness. It is more tear-resistant than asphalt when high winds and foot traffic test the underlayment.
  • Synthetic underlayment is also much more efficient than felt when it comes to moisture absorption. It is much less susceptible to fungal growth and becomes wrinkle-free when compared to felt.
  • As mentioned above, asphalt felt degrades in quality over time when exposed to heat and sunlight. Synthetic underlayment provides longer resistance to ultraviolet rays. Synthetic underlayment is also very dependable during the cold season, while asphalt felt starts to form wrinkles and cracks.
  • Synthetic underlayment rolls are 3.5 feet long and cover about 875 square feet, so installation will take comparatively less time.

Choosing the Right Underlayment for Your Roof

Now that you know the distinct advantages and disadvantages of asphalt felt and synthetic underlayment, you can make a much more informed decision. However, choosing which underlayment type works best for your roof is not a case of preference based on qualities. 

Choosing the proper underlayment depends on your roofing system. For instance, metal roofs should require synthetic underlayment because metal is a heat conductor. It will trap much more heat during the daytime, so you need an underlayment that can easily resist these extreme conditions. In this case, it is synthetic underlayment. 

In contrast, Asphalt-saturated felt underlayment works best with a traditional asphalt shingle roof. Temperatures and weather conditions are more diffuse, which the felt can handle with aplomb.

Lastly, you also need to factor in the climate you live in. If you are in a hot area where summers get scorching, you should choose the more heat-resistant underlayment. This way, your whole roofing system will stand the test of the elements, and your home will stand strong for many years to come!


Asphalt-saturated felt underlayment is a roofing underlayment that has its set of advantages and drawbacks based on the quality and thickness of the material. Its inherent properties make it beneficial for specific environmental and other elemental factors. Choose your underlayment material by considering the roofing system you have, the kind of environment you are in, and the price that suits your budget.

Needing a Roof Underlayment Replacement?

If you require a roof replacement due to missing or damaged shingles and you need the best roof material types, look no further than Southern Premier Roofing residential & commercial roofing. After 15 to 30 years of wear and tear, a replacement may be advised. Always hire a true professional for your roof work in located in several areas, Fayetteville, Hope Mills, Charlotte, and Boise. Contact our experts today!

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