Need a roof replacement? Were you given the option to choose or recommended either felt or synthetic roof underlayment?
Roof underlayment is one of the most important roofing components that every roof needs. The two common types of underlayment used in residential roofing are the old-school felt and new-school synthetic.
Both have their place in roofing, but one is used more than the other. So, the question is felt underlayment or synthetic underlayment the best?
For over 35 years, Bill Ragan Roofing has helped homeowners make the best roofing decisions by simply providing transparent and unbiased advice. So, let's do an honest break down and comparison of felt and synthetic roof underlayment, including pros and cons, durability, pricing, and much more.
By the end of this article, you'll learn:
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.
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.
Both felt and synthetic roof underlayment have their place in the roofing industry. Felt was the preferred underlayment for years, so you’ll still find roofers who use it today.
However, synthetic underlayment was created as technology improved, which means it's considered
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:
Cons:
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:
Cons:
Understanding the pros and cons of both types of underlayment, is great. However, let's breakdown it down more in-depth to understand which roof underlayment is better based on the main comparisons, like weight, price, and more.
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.
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 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 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.
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):
Keep in mind that there are many factors that determine roofing costs, such as:
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.
Synthetic underlayment is by far the better option for roof replacements. Felt underlayment may be cheaper, but the extra durability and protection synthetic provides is well worth the small price difference.
Synthetic underlayment vs. felt underlayment (quick breakdown) |
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| Synthetic underlayment | Comparison | Felt underlayment |
| Lighter | Weight | Heavier (more materials and increase labor cost) |
| Non-skid material | Safe to work on | Slick and bunches up |
| Moisture-resistant | Water repelling | Absorbs water |
| Hard to tear and holds nails well | Durability | Tear prone |
| More expensive, but slightly | Price | Cheaper |
Based on the table and what we've covered it's clear that synthetic roof underlayment is the way to go. Now, if you’re on a really tight budget, felt underlayment may be a consideration.
However, be weary of roofers using felt just to lower prices and hope you don't notice.
While technically it’s own thing, ice and water shield is also a waterproof membrane installed on roof decking that’s fully waterproof. However, high heat ice and water shield is used as underlayment on premium roof systems, such as metal, synthetic, etc.
This is for multiple reasons, but it's not common on standard asphalt shingles. However, while it’s technically not underlayment in most cases, ice and water shield goes hand in hand with it.
Ice and water shield is more commonly used to reinforce vulnerable roof areas prone to leaks (valleys, against walls, etc.) instead of the entire roof decking. For areas that see frequent ice damming, it's also used on the roof's edges to provide more leak protection when the starts to melt.
After reading this article, you know synthetic roof underlayment is the better option over felt underlayment. Felt is still used, but synthetic is by far more commonly used on residential roofs in the United States today.
No matter which you get, the important thing is that underlayment is included in your roof replacement. However, it's just one piece of the puzzle.
Every homeowner getting a new roof needs to know all the components and materials that will be installed. After all, they make up a lot of the cost of your new roof and determine the quality.
That's why I wrote another article breaking down all the crucial roofing materials that must be part of your roof replacement.
Check out 9 Materials Included With Your Roof Replacement to learn what you’re paying for when you get a new roof.