Pros and Cons of 3 Types of Roof Underlayment

Are you unsure what roof underlayment is and why it matters after seeing it listed on a proposal from a roofing contractor? Do you want to know why roofers install underlayment and learn how to assess which type of underlayment is best for you?

At RoofSmart, we do hundreds of roof replacements every year. During each of those projects, we make sure to include underlayment as a base layer on the roof. It is a vital protective layer for the roof, especially in a rainy area like Seattle. But, before the roofing job even begins, we take our customers through our detailed proposal.

Customers often ask why roof underlayment matters and if they even need it. We make sure to educate them on the benefits of roof underlayment and explain their options so that they can choose the one that best fits their needs and budget.

In this article, you’ll learn about the pros and cons of these types of roof underlayment:

1. Felt underlayment
2. Synthetic underlayment
3. Self-Adhered underlayment

By the end, you’ll be able to decide which one is the best fit for your needs, preferences, and budget.

What is roof underlayment used for?

Roof underlayment is used to protect your roof deck or wood substrate from getting wet. It is mainly useful during installation because it keeps the roof deck from absorbing any moisture, which would eventually lead to issues like mold and rotting wood.

Having a barrier to protect your roof from getting wet is extremely valuable in the Greater Seattle area because it rains so often. It allows roofers to continue working in light rain instead of having to wait until it clears up.

It is also beneficial to have underlayment on your roof in case any shingles blow off or water somehow gets underneath the shingles. The underlayment will help protect the roof deck from getting wet.

If the roof got wet without any underlayment on, then water would soak into the roof deck. This can lead to mold. If the water continues to seep in for a while, it can lead to rotting wood and structural damage.

What are the pros and cons of each type of roof underlayment?

Each type of roof underlayment has its own advantages and disadvantages that make them ideal in different situations.

1.) Felt Underlayment

Up until about 10 years ago, this was the only roof underlayment option available. This type of underlayment is used for the entire roof deck.

• Pros:
  • This is the most affordable roof underlayment option that still meets the code requirements for roof installation. It usually costs 20 cents per square foot.
  • It is very breathable. Some people like felt because they feel that it has more elasticity (although synthetic underlayment is also flexible).

• Cons:
  • Felt underlayment tears easily.
  • And, when it gets exposed to the elements it can absorb water and wrinkle. These wrinkles can distort the shingles (especially if you’re using a 3-tab shingle). To get rid of wrinkles, the roofer can cut through them and lay the underlayment flat. This is a problem because your underlayment will have big slices through it.
  • For that reason, felt underlayment is no longer popular in the Greater Seattle area. With the amount of rain that we get, many roofing contractors and homeowners prefer synthetic underlayment.

2.) Synthetic Underlayment

This is the most common type of underlayment used across the entire roof deck. It has only been around for about 10 years.

• Pros:
  • Synthetic underlayment has a higher amount of tear resistance than felt. Overall, it has greater strength and durability over time.
  • When it gets wet, this type of underlayment does not absorb water or wrinkle. It keeps water off of the roof while maintaining its structural integrity. The shingles can be installed right on top of it with no issues, even if it is wet. It is a good option for covering a roof during rainy weather.
  • It is also safer for your roofing contractor to walk on than felt underlayment because it provides better traction.

• Cons:
  • It is more expensive than felt (but it is not the most expensive underlayment option). It usually costs 25 cents per square foot (but there are different grades of it that may cost more or less).

3.) Self-Adhered Underlayment

Most people do not use this type of underlayment as the standard. It is mainly installed in areas that are at a higher risk for leaking (not over the whole roof deck). It’s commonly used on lower-pitch roofs, valleys, chimneys, skylights, and any spots that tend to be at a higher risk of leaking.

• Pros:
  • A major advantage to adhesive underlayment is that it self-seals around the nail holes, which gives it better protection against rain and moisture (but not all of them do this). Water is far less likely to get underneath it if the hole around the nail is sealed.
  • It sticks right to the roof deck to help create a strong seal. It also provides a safe walking surface for roofers.

• Cons:
  • It is the most expensive underlayment option, which is why people rarely use it across the whole roof deck. If they did, it would be about $1.25 per square foot to install it.

When is each type of roof underlayment the best fit?

It is up to you to decide which underlayment is best for your roof. Most homeowners in the Greater Seattle area end up using synthetic underlayment, so you might find that it will also work best for you. But, it all depends on your specific circumstances.

Each type of underlayment has its own benefits that might make it a good fit for you. You’ll want to consider your budget, your roof’s needs, and the environment that you live in while making your decision.

If you are looking for the most affordable underlayment option, then felt is a good choice for you. It has the lowest prices of all the options.

Even though felt underlayment meets code requirements, you might find that you want a higher level of protection. If that is the case, then synthetic underlayment is a good option because it can repel water without being damaged.

If you want more protection beyond that and are concerned about certain areas of the roof that are prone to leaking, then adhesive underlayment might be right for you.

For example, if there is a part of your roof that has the wind blowing in water up under the shingles or in directions where it’s not supposed to go, adhesive underlayment gives the added protection you need to help prevent leaks.

Deciding Which Roof Underlayment Is Right for You

Choosing the right roof underlayment depends on your specific needs, budget, and the challenges posed by your environment—especially in rainy areas like Seattle. By understanding the pros and cons of each type of underlayment, you’re equipped to make the best decision for your roof’s long-term protection.

If you’re unfamiliar with underlayment and want to make sure that you’re getting the right kind for you at a reasonable price, then it’s important to find a roofer that is experienced and trustworthy. A qualified roofer will be willing to explain underlayment to you and discuss costs.

Need help figuring out how to find an experienced, qualified roofing contractor that you can trust? Read our article “How Do I Know If A Roofing Contractor is Qualified?” to guide your search for a competent, experienced roofing contractor.