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Synthetic Underlayment vs. Felt Underlayment: Which Is Right For Your Roof?

Posted on March 23, 2024

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synthetic underlayment vs felt

Deciding between synthetic underlayment and felt underlayment for your roof is not always as clear-cut as you may think. These two types of roof underlayments have differing advantages, shortcomings, features, and demands that require careful consideration before making a final decision. 

As a homeowner or contractor aiming to make an informed choice, understanding these options is essential. Luckily, this blog post is for you! Continue reading this guide on synthetic underlayment vs. felt to know which one is the right choice for your roof. 

Understanding What Felt and Synthetic Underlayment Is

Before discussing the debate between synthetic vs. felt underlayment, let’s first try to understand what these two types of underlayment are. 

1. Felt Underlayment

Felt underlayment

Felt underlayment, often referred to as felt paper or tar paper, is traditionally manufactured from natural materials. If you dig a little deeper, you’ll find that it’s primarily made from recycled waste paper mixed with asphalt. This composition allows it to effectively create a waterproof barrier on your roof. 

Felt roofing underlayment is available in two primary types: #15, and #30. These are otherwise known and labeled as 15-pound and 30-pound underlayment due to the way that the number represents the thickness of the material. This means that a #30 felt is twice as thick as its counterpart, providing enhanced durability and longevity at an additional cost, as expected. 

2. Synthetic Underlayment

Synthetic underlayment

As the name suggests, synthetic underlayment is made using man-made materials that offer superior performance compared to traditional organic options. Polyethylene or polypropylene are commonly used materials in this category. These materials are well-known for their exceptional toughness yet lightweight feel.

The combination of the robustness of these materials with the advanced manufacturing process results in a surprisingly durable, waterproof layer that provides better protection against harsh weather conditions compared to felt.

While synthetic roof underlayment is made using an advanced manufacturing process, they aren’t without their problems. To learn more, check out: 7 Common Problems With Synthetic Roof Underlayment

Synthetic Underlayment vs. Felt: A Sharp Line Between The Two

When it comes to felt vs. synthetic underlayment, the comparison is all about understanding the characteristics of each. Specifically, two key factors come into play: durability and resistance to elements. Let’s dive into how felt and synthetic underlayment measure up.

1. Durability and Resistance to Elements

Both durability and weather resistance are tremendously important in terms of roofing materials. After all, your roof takes a beating from the sun’s harsh UV rays, pouring rain, heavy snowfall, and gusty winds. 

Longevity of Felt Underlayment

Felt has been a favorite choice for decades due to its substantial durability. Traditionally composed of a blend of natural materials such as cellulose (wood) fibers mixed with bitumen (asphalt), felt underlayment boasts a lifespan typically averaging 20 to 30 years. 

However, this longevity comes with some downsides. Namely, because it’s made largely from organic matter, felt doesn’t do well in damp environments. It absorbs water instead of repelling it, which can lead to swelling or buckling of the roofing material laid on top of it over time.

Longevity of Synthetic Underlayment

When we look at synthetic underlayment, it offers superior durability compared to its traditional counterparts. Since it’s constructed using high-quality polymers like polypropylene or polyester fiber mesh infused with plastic layers for added strength and water resistance, these materials offer extreme durability.

Moreover, many quality brands guarantee their synthetic underlayment can last for 50 years or even a lifetime, depending entirely on the product and manufacturer. 

Because they are engineered to resist UV exposure and withstand extreme weather conditions, synthetic underlayments thrive where felt ones have shortcomings, especially in regard to wetter climates.

2. How Long Can Roof Underlayment Be Left Exposed? 

When installing a new roof, homeowners often ask us, how long can roof underlayment be exposed? This question may also come into play if you find that roofing materials such as shingles have blown off the roof. The difference in the amount of time roof underlayment can remain exposed depends on whether it’s made out of felt or synthetic material. 

Felt Underlayment

Let’s be clear, in terms of exposure time, felt isn’t the most resilient option. While the exact time can vary based on factors such as climate conditions, generally speaking, #15 felt should not remain exposed longer than a month. For #30 felt, the accepted exposure time can extend up to two months.

Due to its organic nature and composition (being made of cellulose), tar paper tends to degrade faster when in direct contact with UV rays or rainwater, and as a result prolonged exposure can lead to curling edges or tearing which hinders its waterproof capabilities.

Synthetic Underlayment

Expert roofing contractors suggest synthetic roof underlayments can typically withstand exposure for up to six months without a significant decline in performance.

Unlike their felt counterpart, they offer advantages like a higher resistance to wind uplift and UV rays. Furthermore, synthetic roof underlayment is waterproof! Their non-absorbent surface effectively prevents water infiltration while enhancing your roof’s overall weather protection system.

Synthetic Underlayment vs. Felt: Which Is Better For Your Home? 

Even if you know the pros and cons of synthetic and felt underlayment, it can be daunting to make a final decision. No homeowner wants to settle for something less than the best when it comes to their home’s protection, so you will need to consider additional factors to choose the right one confidently. 

Here are some of those factors: 

1. Consider Your Climate

When choosing roof underlayment for your home, it is essential to factor in your local climate, as it can impact how effective your underlayment is.

If your area experiences harsh winters or heavy rainfall frequently, synthetic underlayment might be a better fit. However, for areas with mostly dry climates, a high-quality felt underlayment could be the right choice. 

2. Think About Your Budget

While each type of underlayment serves its purpose well within its respective price range, synthetic options are typically more expensive upfront. However, the material’s longevity and enhanced durability against weather elements may make it a more cost-effective choice in the long run. But if you’re on a strict budget and looking for an affordable solution, felt roof underlayment can do the job effectively. 

3. Consider Your Desired Installation Timeline

Synthetic underlayment is often lighter to handle and quicker to install than its felt counterpart. This means less time is needed for labor, and therefore, you’ll be dealing with cheaper installation costs. 

Final Thoughts

As we’ve discussed, there’s no one-size-fits-all answer when it comes to choosing between synthetic underlayment vs. felt. Your choice completely depends on a variety of factors, including your local climate, budget, and the desired timeline for completing your project. 

To make an informed decision, it’s important to discuss these factors in detail with trusted professionals. By doing so, you’ll be able to select the right type of underlayment for your needs.

Contact A. Fricker Roofing and Waterproofing In Tulsa, OK, For Your Roof Replacement

Now that you know the difference between synthetic and felt underlayments, it is easy for you to make an informed decision. However, we always recommend that homeowners consult with a professional roofer in their area to discuss their roofing needs. 

If you are considering a roof replacement for your home or commercial building, talk with one of our expert roofers at A. Fricker Roofing and Waterproofing in Tulsa, OK. 
Our skilled professionals can proficiently handle any roofing project, whether it’s a new roof installation or a complete roof replacement. Contact us today at (918) 402-7167 to find out more about how we can help you!

synthetic underlayment vs felt