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Asphalt Shingle Roof | Roofing materials

What’s the Best Type of Underlayment for Asphalt Shingles?

February 27th, 2023 | 4 min. read

What’s the Best Type of Underlayment for Asphalt Shingles?

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Underlayment plays a vital role on an asphalt shingle roof. So, it makes sense to look for the best type of underlayment when it’s time for a roof replacement. 

The truth is, you can’t go wrong with the type of underlayment you choose. The important thing is that it’s installed on your asphalt roof properly.

However, there is one type of underlayment that most roofing contractors agree on being the “best”. 

For over 30 years, the team at Bill Ragan Roofing has helped homeowners understand the different roofing components and the recommended choice for each one. Now I’ll do the same thing for you by breaking down the best type of roof underlayment for an asphalt shingle roof. 

This article starts with a brief explanation of what underlayment is and the two types. After that, you’ll learn the best type of underlayment for an asphalt shingle roof and why it’s recommended.  

What is roof underlayment?

Roof underlayment is the roofing component installed directly over your roof decking. It lies between the decking and your asphalt shingles to provide an extra layer of protection from the elements.

synthetic roof underlayment installed over roof decking before asphalt shingles are installed(Synthetic underlayment installed over roof decking)

There are two types of roof underlayment for asphalt shingles: felt underlayment and synthetic underlayment. 

So, before we get to one which underlayment is best for asphalt shingles, you need to know the difference between the two types. 

Felt underlayment is the older of the two and comes in 15 lb and 30 lb rolls. The big difference between the two types of felt underlayment is that 30 lb is thicker, stronger, and less likely to tear than 15 lb.

Synthetic underlayment has been around for about 20 years and is made of woven/spun polyethylene or polypropylene. No matter which underlayment you choose, it’s a crucial roofing component that every roof needs. 

What’s the best type of underlayment for asphalt shingles?

Both types of roof underlayment do the job, and you can’t go wrong either way. However, I always recommend synthetic underlayment when getting asphalt shingles installed. 

The reason for this simply comes down to durability, functionality, and pricing. Let’s dig deeper into these reasons, so you fully understand why synthetic underlayment is the best choice for asphalt shingles.

Synthetic underlayment weighs less than felt underlayment

You probably don’t think the weight of underlayment is that important. However, the weight actually impacts the labor cost of your roof replacement

Synthetic underlayment weighs less than felt underlayment. Due to felt underlayment being heavier, it doesn’t have as much material per roll as synthetic underlayment. 

This leads to using more rolls, which takes more time and manpower to get up the ladder for installation. This won’t add much  to the labor cost, but it is a reason why roofing contractors prefer synthetic underlayment. 

Synthetic underlayment is more durable and safer than felt underlayment

The biggest reason I recommend synthetic underlayment for asphalt shingles is that it’s more durable than felt underlayment. Felt underlayment is more prone to rip in the event of high winds, which leaves your decking exposed to water. 

Even if it doesn’t get ripped by the wind, it’ll absorb and hold water when it gets wet. This not only leads to an eventual leak, but it’ll also rot your roof decking. 

Synthetic underlayment does the opposite and repels water if it gets wet. It also holds roofing nails better than felt underlayment. 

Another big reason why roofing contractors recommend synthetic underlayment is for safety reasons. Synthetic underlayment is a non-skid material, so you don’t have to worry about it tearing or crew members slipping.

This makes it safer for your roofer to work as they install your asphalt shingles.  

Synthetic underlayment isn’t that much more expensive than felt underlayment

While roof underlayment is an important component, it doesn’t have a huge impact on the overall cost of a new roof. With that in mind, synthetic roof underlayment does cost more than felt roof underlayment. 

Even though it costs more, synthetic underlayment isn’t much more expensive. But I understand pricing is a huge factor in the decision-making process. 

While the initial material investment is higher, synthetic underlayment is a better quality material that offers more benefits than felt underlayment. But at the end of the day, it’s up to you to choose the right roof underlayment for your situation. 

What are the rest of the components of an asphalt shingle roof?

Now you know why I recommend synthetic roof underlayment and consider it the “best” for asphalt shingles. Remember, both types of underlayment do the job of protecting your roof decking. 

Synthetic underlayment’s benefits simply make it the better option, and it gives you more peace of mind than felt underlayment. Regardless of which one you choose, your asphalt shingle roof must have underlayment. 

But underlayment is just one important piece of a roof system that must be included in a replacement. The last thing you want is to invest in a new asphalt roof and later learn it’s missing a crucial component. 

That’s why you need to know the rest of an asphalt shingle roof’s components to ensure everything is included in your roof estimate.

Check out this article on The 9 Asphalt Shingle Roof Components to learn all the components and materials that make up an asphalt roof system.

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