Key Takeaways
- Underlayment sits between the roof deck and the shingles. It’s the secondary water barrier that goes under shingles, metal, or tile, and it protects the deck when moisture gets past the finished roof covering. Once the roof is on, you never see it again.
- Felt is water-resistant, not waterproof. Asphalt-saturated felt holds off water infiltration well, but it wrinkles once it gets wet, and wrinkled felt shields the deck poorly. It comes in 15-pound and 30-pound weights, with 30-pound used on steep-pitch roofs, and it can last up to 30 years when it’s installed right.
- Synthetic underlayment is polymer-based and hard to tear. It’s made from polyethylene and polypropylene, so it stands up to tearing and UV exposure through a long Texas tear-off. It also puts less weight on older roof structures, and it protects better than felt when a storm strips shingles.
- Synthetic acts as a vapor barrier, so ventilation matters. On a roof that doesn’t vent well, synthetic can be the wrong call. There’s also no manufacturing standard governing what goes into synthetic underlayment, so quality varies a lot from product to product.
- Building codes and shingle warranties can decide this for you. Some local codes still require felt. Some shingle manufacturers require synthetic to keep warranty coverage valid, and using the wrong one can void it. Check both before you pick on price.
Roof underlayment is an important layer of the roofing system, installed between the roof deck and the shingles, metal, tile, or other primary roof covering. It provides a secondary layer of protection for the roof deck if moisture gets beneath the finished roofing material.
Two of the most common options are traditional asphalt-saturated felt and synthetic roof underlayment. Both can be appropriate roofing materials, but they differ in weight, tear resistance, moisture resistance, installation, cost, and product-specific performance.
In this guide, we’ll compare synthetic vs. felt roof underlayment, explain the pros and cons of each, and discuss what Dallas-Fort Worth homeowners should consider when choosing an underlayment for a new or replacement roof.
What Is Roofing Underlayment?
Simply defined, roof underlayment is the layer of your roofing system that is situated between the sheathing and the outermost layer of your roof. When you look at your roof, you won’t be able to see your underlayment level because it’ll be covered by your shingles or other roofing material. It’s important to note that roof underlayment provides a secondary moisture barrier to help keep your home dry from the elements. It goes a long way in preserving your overall roof’s lifespan and enhancing its performance.
Why Is Roofing Underlayment Important?
Your primary roofing material is designed to handle most of the weather your roof receives, but it is not the only layer protecting the roof deck. Underlayment provides an additional layer beneath shingles, metal, tile, or other roofing materials that can help protect the deck from moisture that reaches beneath the finished roof covering.
Underlayment can also help create a smooth surface for installation and provide temporary protection to the roof deck during the roofing process. The performance requirements depend on the roofing system and the specific underlayment being installed.
Underlayment selection may also affect manufacturer requirements, roofing-system approvals, and warranty eligibility. Homeowners should follow the specifications for the roofing material being installed rather than assuming that every type of underlayment is interchangeable.
Felt Underlayment
Felt is considered one of the most traditional underlayment roofing materials. It’s typically constructed of a compound of organic materials or fiberglass mixed with asphalt. While felt underlayment is not completely waterproof, it’s highly resistant to water infiltration. It’s a very durable material that has been shown to last up to 30 years when installed properly.
Most felt underlayment is available in different thicknesses ranging from 15 to 30 pounds. If your roof has a very steep pitch, you’ll want to go with the 30-pound felt as it’s more resistant to damage. However, if your roof doesn’t have a very steep pitch, you can get away with the 15-pound felt. All felt underlayment is attached with either staples or plastic caps. The latter has been shown to be more resistant to strong wind gusts and water leakage.
One of the biggest advantages of using felt underlayment is its extreme affordability. It does meet all building codes and has been proven to be effective for literal decades. However, felt underlayment does come along with some drawbacks. It’s more dangerous to work on for installation purposes and is more prone to ripping or tearing during installation. It’s a very heavy material to carry around, and it will wrinkle up when it’s exposed to moisture. You may find that it will cost more for labor to have felt underlayment installed on your roof as compared to installing a synthetic underlayment.
Synthetic Underlayment
Synthetic underlayment is considered a newer material that’s gained a lot of popularity in recent decades. It’s constructed of long-lasting polymers, like polyethylene and polypropylene. Synthetic underlayment is extremely difficult to tear and can withstand exposure to ultraviolet rays from the sun. It’s very moisture-resistant and is much thinner than felt. It’s a very lightweight material that’s easier to carry around as well as easier to install. It also will put less weight on your roof, which is ideal for older homes with a less rigid roofing structure.
While synthetic underlayment has a lot of benefits over traditional felt underlayment, it does have some drawbacks that go along with it. Some building codes have not yet caught up to using synthetic underlayment and still require the use of felt underlayment. Synthetic underlayment tends to be more expensive to purchase than felt.
It’s important to note that synthetic underlayment acts as a vapor barrier for your roof. If your rooftop doesn’t get adequate ventilation, then synthetic may not be the best underlayment option. You should also be aware of the fact that there’s no manufacturing standard for the components that must be put in synthetic underlayment. So, you’ll want to consult one of our experienced roofers to determine synthetic underlayment products that are of good quality.
Some Factors to Consider
When deciding between felt and synthetic underlayment, there are a few different key factors you’ll want to take into consideration. First and most obvious, you’ll need to determine the building codes in your area to ensure that you’re not required to install only felt underlayment. Second, you want to look at the warranty information for the type of roofing material that you’re going to have installed.
For example, some shingle manufacturers may require that you have synthetic underlayment under their shingles in order to maintain warranty coverage. If you were to use felt instead, they could actually void the warranty coverage and leave you paying out of pocket for any defects.
Another factor you’ll need to consider is the roofing contractor that you hire. It’s well-known that synthetic underlayment is lighter to carry, safer to walk on, and less prone to damage during installation. For these reasons, particular roofing contractors may only offer the installation of synthetic underlayment. You should check with your roofing provider to see if they have any restrictions as far as what they’re willing to install.
One factor that you simply can’t overlook is the overall budget you have for the project. There’s no doubt that going with felt underlayment will be much cheaper than using a synthetic underlayment. However, it’s important to keep in mind that felt underlayment will not stand up as well to moisture and mold.
In the event that your roof ends up missing some of its shingles due to a nasty storm, synthetic underlayment will be more effective at protecting your home than felt underlayment. Felt will simply wrinkle when it comes into contact with moisture, which will reduce its overall effectiveness at protecting your home.
Choosing Underlayment For Dallas Weather
Underlayment is your secondary water barrier, and choices should reflect steep heat cycles, wind-driven rain, and hail events common across DFW. Synthetic sheets resist wrinkling and UV better during long Texas tear-offs, while modern felts remain a budget-friendly option for simple roofs with quick dry-in. Attachment pattern, edge metal integration, and valley treatment matter as much as material grade.
Pair underlayment selection with your primary roofing. Architectural shingles benefit from high-grip surfaces and ice-and-water shields in valleys. See options on asphalt shingles. Metal systems need high-temp, smooth underlayments under clips and seams to reduce abrasion and heat. Explore standing seam metal details. Live in a storm corridor? Reinforce eaves and rakes and schedule a post-install check after major weather with our storm damage team.
Quality Roof Installation Service
KPost Company provides quality roof installation service for community members throughout the entire Dallas, TX area. We can also help with all your solar, emergency repair, roof inspection, gutter installation, storm damage, roof replacement, and roof maintenance needs. Give us a call today to schedule a consultation with one of our highly experienced roofers.
