Are you about to replace your asphalt shingle roof? Do you want to ensure you get a high-quality roof with the best underlayment and other roofing components?
Looking for quality over a low price is the best mindset to have when getting a new roof. It not only helps you avoid bad roofers, but it also ensures you don't get their cheap products.
And one of the easiest ways to bring down prices is by offering lower grade underlayment. But underlayment plays such a vital roll as your roof's last line of defense against leaks.
Now, the important thing is that it’s installed on your asphalt roof properly in general. However, there is one type of underlayment that most roofing contractors agree on being the “best”.
For over 35 years, 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.
By the end of this article, you'll learn:
- What is roof underlayment? (Types, pros, and cons)
- What’s the best type of underlayment for asphalt shingles? (plus the reasons why)
What is roof underlayment?
Roof underlayment is a water-resistant roofing component installed directly over the top of your roof decking. It's between the decking and roofing material to provide an extra layer of protection from the elements.
(Example of synthetic underlayment installed)
Think of it as a safety net if water gets under your shingles that prevents it from getting to the wood underneath. Underlayment also acts as a barrier if shingles get blown off during storms with high winds.
However, 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 roof underlayment
The “old-school” underlayment that was used before the invention of synthetic underlayment. It’s made from a paper or fiberglass mat soaked in asphalt that comes in 15lb or 30lb.
Pros of felt underlayment:
- Cheap
- Better than having no underlayment
Cons of felt underlayment:
- Tears easily in high winds
- Absorbs water rather than repelling it
- Not ideal for humid climates
Synthetic roof underlayment
Synthetic underlayment is made from woven/spun polyethylene or polypropylene polymers that resist tearing and moisture. This is the standard roof underlayment used on most homes in the United States.
Pros of synthetic underlayment:
- Tear-resistant in wind
- Repels water
- Lightweight
- Safer for installers to walk on
- Performs well in heat and humidity
Cons of synthetic underlayment:
- Slightly more expensive than felt
What’s the best type of underlayment for asphalt shingles?
Both types of roof underlayment do the job, but synthetic underlayment is by far the best option for asphalt shingles. 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
Weight may not seem like but a big deal, but it actually impacts the labor cost of your roof replacement. Felt underlayment weighs more than synthetic underlayment, meaning it doesn’t have as much material per roll as synthetic.
This leads to needing more more rolls of it, which takes more time and manpower to get it up the ladder and install it on your roof. While this doesn't skyrocket labor costs, it’s just something to keep in mind.
Synthetic underlayment is safer to work on
Once your underlayment is installed, the roofers will start to install the main roofing material. Well, they have to walk around to do this.
Because synthetic underlayment is made to be non-skid, it’s a lot safer to work on for crew. This means even as they're walking on it and installing the rest of your roof, they’ll feel safe and won’t have to worry about slipping like they would on felt underlayment.
Synthetic underlayment is more durable
Synthetic underlayment is more durable than felt underlayment. This is mainly due to the material, but synthetic underlayment also holds nails better than felt.
Felt underlayment is much more prone to rip from high winds and movement during the installation process. While felt does do the job, synthetic underlayment provides added strength and protects your roof from weather better than felt.
Synthetic underlayment repels water instead of absorbing it
Synthetic roof underlayment is specifically made to repel water, but felt isn't. So, if your shingles blow off, water wicks off synthetic underlayment while felt underlayment won't.
Instead, felt underlayment absorbs water or moisture when exposed to it. On top of this, it wrinkles when wet, which is why shingles need to be installed as soon as felt underlayment is laid down to avoid bunching up or moisture absorption.
Synthetic underlayment isn't much more expensive than felt
The cost of roof underlayment is included in the overall cost of your roof replacement, so it’s impossible to nail down an exact price. However, synthetic underlayment is more expensive than felt, but just slightly.
Typical roof underlayment cost ranges (material costs only):
- Felt underlayment: around $0.25 per square foot
- Synthetic underlayment: $0.25–$0.50+ per square foot
Keep in mind that there are many factors that determine roofing costs, such as:
- Roof pitch
- Roof size
- Number of valleys, walls, penetrations, etc.
- Underlayment brand
- Local supplier costs and labor rates in your area
At the end of the day, roof underlayment is wrapped into the overall price of your roof replacement. However, it must be included on every roof, so it will always affect the cost.
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 The 10 Asphalt Shingle Roof Components to learn all the components and materials that make up an asphalt roof system.
