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Synthetic Underlayments Versus Felt

Why you should switch to synthetics

Mcn Kyp Owens Corning Oct17 2
Today’s roofing contractor has plenty to keep in mind: price pressures, safety, code compliance, maintaining a staff of quality installers, not to mention keeping homeowners happy. In the midst of these concerns, it can be easy to overlook a critical component of a high-performance roofing system: the underlayment.

For decades, felt paper was the only underlayment option. As synthetics came along about two decades ago, the benefits they offered in terms of safety, ease of use and durability were unquestionable, but also came with a high price tag. As technology advanced in synthetic product development, prices became more affordable. In fact, many synthetics now feature a price point between what contractors would pay for #15 or #30 felt. Some contractors have stayed with felt just out of habit. When they have a chance to sample synthetic underlayment on the job, many leave felt behind and never look back. The benefits in safety and performance far outweigh the minimal additional cost, and many contractors also find the synthetics can be a great point of differentiation in their roofing systems, truly adding a layer of quality to their final product.

So, what makes synthetic underlayments so attractive to contractors and homeowners? There are four main reasons why so many contractors are making the switch to synthetics.

Improved Safety

Although not a replacement for fall protection, synthetics provide a slip-resistant walking surface that allows installers to move around the roof with ease when installing all components in a metal roof system. Many synthetics have a lighter, cooler surface color (like grey), which creates more comfortable working conditions in hot weather. The products are lightweight, easy to handle, and contain more material per roll than #15 or #30 felt paper, all of which are key considerations for minimizing material movement on and around the roof. In a tight labor market, these features can be a selling point for recruiting installers; workers feel better knowing their employer uses materials that help keep them safe and comfortable on the job.

Synthetics are Tougher

Synthetics resist tearing far better than felt. This is easy to demonstrate, just take a piece of #15 or #30 felt paper and note how easy it is to tear it in half. The same will not be true with synthetics. Higher strength means less tearing around fasteners during installation and fewer opportunities for water infiltration. Further, synthetic products can be left exposed to ultraviolet (UV) light for 30 to 180 days before covering with the primary roof covering. Felt products do not offer this level of protection, they will wrinkle and degrade with extended exposure. Finally, synthetic underlayment can withstand high surface temperatures up to 240 F, making them an ideal product for metal roofing applications.

Faster to Install

Synthetic underlayments are printed with overlap and nailing guides on the product. As well, clear installation instructions are provided with synthetics; making the products fast and easy to install. Synthetic rolls are lighter, wider and longer than #15 or #30 felt. This allows for fewer trips up the ladder, faster deck coverage and a reduced number of laps and cuts. Because they contain more material per roll than felt, synthetics can shorten installation time. In short, synthetics allow for an efficient installation, which is a big reason why these products are in demand by contractors.

Synthetics Repel Water

A primary purpose of underlayment is to be a second line of defense against water infiltration. A roof is a big investment, and most homeowners want to know their home is protected if water finds its way beneath the primary roof covering. Unlike felt underlayments that absorb water, synthetics are manufactured to repel and shed water. Further, synthetics are not a food source for mold, unlike felt. These attributes provide homeowners peace of mind that their home will be protected against water infiltration and mold growth.

There are three things a good roof should do: It should seal the home from water and ice damming damage, defend the home against the elements and allow the home to breathe through proper balanced ventilation. Synthetic underlayments are a critical part of the seal equation, creating a durable, tough barrier of protection before a single roofing panel is installed. Unlike many felt products, they carry a limited warranty, and provide numerous performance advantages as discussed in this article. It is no surprise that synthetics are becoming the preferred underlayment product in most markets. They are highly engineered products designed to provide next generation performance for today’s roofing systems.

Chris Kasprzak is a product manager at Owens Corning in Toledo, Ohio. To learn more, visit