The Difference Between Synthetic Underlayment and Felt
When it's time to install or replace your roof, most homeowners focus on shingles, but there's another essential layer you should know about—the underlayment. This layer sits between the roof deck (the wooden structure) and the shingles, providing an extra defense against the elements. The two most common types are synthetic underlayment and traditional felt underlayment. Understanding the differences between the two can help you make the best choice for your home.
What is Roof Underlayment?
Underlayment is a protective sheet installed directly on your roof deck before the shingles go on. Its main job is to provide a waterproof barrier and extra layer of protection. While your shingles bear the brunt of sun, rain, and wind, underlayment adds another line of defense, especially during extreme weather. So, choosing the right underlayment is key to keeping your home safe and dry.
Synthetic Underlayment: The New Roofing Standard
In recent years, synthetic underlayment has become the top choice for roofing professionals, and for good reason. It’s made from high-quality polymers, which provide a stronger, more reliable layer of protection.
Superior Durability: Synthetic underlayment is designed to resist tears, punctures, and wear, even in harsh conditions. This means it will hold up better during installation and against strong winds or storms. Felt, by comparison, is more prone to ripping or weakening over time.
Waterproof Protection: One of the biggest benefits of synthetic underlayment is that it repels water. Because it doesn't absorb moisture like felt does, it provides much better protection against water damage. This can help prevent leaks and mold, which are common issues in roofs that use felt underlayment.
Lightweight and Easy to Work With: Synthetic underlayment is lighter than felt, which makes it easier for roofing crews to install. Its lighter weight also means less stress on your roof deck. This results in faster, more efficient installation and fewer opportunities for errors that can cause problems down the line.
UV Resistant and Long-Lasting: Synthetic underlayment can be exposed to UV rays for a longer period without breaking down, giving it more longevity during installation delays. This can be especially helpful if weather or scheduling issues cause a pause in your roofing project. Felt, on the other hand, becomes brittle when exposed to the sun for too long.
Longer Lifespan: Because synthetic underlayment is so durable, it typically outlasts traditional felt by several years. This means less maintenance, fewer repairs, and a longer-lasting roof that provides reliable protection throughout its lifespan.
Felt Underlayment: Still in Use, But Not Ideal
Felt underlayment has been the traditional choice for many years, but it’s becoming less common due to its limitations:
Prone to Tearing: Felt is made from paper or fiberglass mat that is soaked in asphalt, which makes it thicker and more rigid. However, this also makes it more prone to tearing during installation, especially if roofers are working in windy or wet conditions. A torn underlayment exposes your roof deck to potential water damage.
Water Absorption: One of the biggest downsides of felt is that it absorbs water. When it gets wet, it wrinkles and bubbles, creating gaps that can let moisture through. Over time, this can lead to mold growth, wood rot, and leaks, which are expensive to repair.
Heavy and Bulky: Felt underlayment is heavier and bulkier than synthetic, making it harder to handle and install. The added weight can also make it sag between roof rafters, which can cause further problems down the road.
UV Sensitivity: Felt doesn’t stand up well to prolonged exposure to the sun. If there’s any delay in the installation of your shingles, felt can dry out and become brittle, making it less effective at protecting your roof.
Building Codes: Why Synthetic is Now Required
A major reason to choose synthetic underlayment is that it's required by building codes in many areas. As roofing technology has advanced, synthetic underlayment has become the industry standard due to its superior performance and safety benefits. In many places, felt underlayment no longer meets building codes because it doesn’t offer the same level of protection.
Using materials that don’t meet code can lead to problems during inspections, delays in your project, and potential issues with warranties or selling your home in the future. Sticking with synthetic underlayment ensures your roof is up to code and fully compliant with local regulations.
Which Should You Choose?
When it comes to protecting your roof and home, synthetic underlayment is the clear winner. It’s more durable, waterproof, easier to install, and meets modern building codes. While felt is still used in some cases, it simply doesn’t offer the same level of protection or long-term reliability as synthetic.
Choosing synthetic underlayment is an investment in your roof’s future, ensuring it can withstand whatever nature throws at it—whether it’s wind, rain, snow, or heat. The added durability and compliance with building codes make synthetic underlayment the best choice for homeowners who want peace of mind and a roof that lasts for years to come.
