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For roofers making the choice between asphalt felt versus synthetic underlayments, there are a lot of factors to consider. Asphalt has been the standard for decades, and it remains a popular choice because roofers are familiar with it and because it’s typically cheaper to install. The price for #30 felt averages around 10 cents per square foot while synthetics can cost between 11 and 15 cents a square foot.

Synthetic underlayment—apart from peel-and-stick varieties, which are self-sealing—also require cap fasteners to prevent leaks whereas asphalt felt can be installed with less expensive nails or staples.

But on the plus side, synthetic underlayment is much more durable than asphalt. It’s less likely to tear, and when properly installed, less prone to leaks, too. It also comes with other advantages—lighter weight, which makes it easier to handle and install, and it isn’t prone to wrinkling during installation the way asphalt can, for instance.

Above all else, though, synthetic underlayments can handle much longer exposure than asphalt felt. How do the two compare in terms of exposure? Let’s take a look.

Asphalt Versus Synthetic: Exposure Times

Most asphalt felt doesn’t give exposure times because this product is designed to be covered immediately. In wet weather, it wrinkles, cold will make it crack, and high temperatures and UV rays both will degrade the material rather quickly. All of this means that asphalt felt should only be used when the roof will be covered in the same day.

Synthetic underlayment, on the other hand, is resistant to moisture and extreme temperatures. In addition, it typically resists UV damage for between six to 12 months. This is pretty standard across all synthetic underlayment brands, but looking at Epilay products in particular, all of our Protectite products—Platinum, Ultra, Superior and Plasfelt—are rated to withstand up to one year’s exposure. Plystick Plus, our peel-and-stick underlayment, can be left exposed for up to six months.

Why Choose Underlayment with Longer Exposure Ratings?

There are lots of reasons why you’d want that six months to a year’s worth of exposure time. On large scale projects, for example, the work might be done in stages, making it difficult to cover the roofing with underlayment in the same day.

Builders always have to worry about supply delays, too. If a shipment of materials is late for whatever reason, or if you’ve scheduled an order for roofing material that might take some time to arrive, then synthetic underlayment will let you get the underlayment down so that you can focus on other parts of the project while you wait.

It’s also an extra insurance policy for homeowners, especially in storm-prone areas. In the aftermath of tornados, hurricanes or straight-line winds, there could be dozens or hundreds of homes in the affected area that require roof repair. This makes it a challenge both for homeowners, who need something covering their rooftop right away, and for roofers, who are hard pressed to serve everyone in need. Homeowners with synthetic underlayment can rest in peace, knowing that so long as the underlayment is intact, they can safely wait until roofers are able to make the repairs.

Of all the reasons to choose synthetic underlayment, exposure times are one of the best. If for any reason you need to leave a roof uncovered for a short period, then synthetic products give you the ability to safely do so.