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Synthetic underlayments have been around for a while, but prior to their development, roofing felt was the industry standard. More and more, builders are switching to synthetics, but some still have questions about which products to choose. If you’re thinking about using a synthetic underlayment for a metal roofing project, here are some of those questions answered!

Why Does Metal Roofing Need Underlayment?

The most important reason to install underlayment beneath a metal roofing system is to prevent water damage. Primarily, the underlayment is there to stand as a barrier between moisture and the roof deck, preventing damage caused by wind-driven rain that may infiltrate seams, or water that might seep in around fasteners as things like snow and ice start to melt.

Another important reason to install underlayment is to prevent damage caused by ice dams. These are the ridges of snow and ice that often accumulate along the edges of a rooftop. The problem here is that ice dams trap water on the roof—and that trapped water can seep in around fasteners and seams, so the underlayment is there to prevent that water from reaching the wood beneath.

What Type of Underlayment Should You Use?

The choice for underlayment beneath a metal roof comes down to traditional roofing felt or one of the newer synthetic underlayments available today. Felt is a popular choice not only because it was the industry standard prior to the development of synthetics, but also because it is inexpensive, and most roofers are used to working with it. In many cases, traditional felt works well—but be mindful that it has one key drawback, which is that it isn’t watertight. What this means is that if moisture seeps through the metal, then it could also eventually seep through the felt, too. That’s one reason why this type of underlayment is best suited to dry climates where moisture is in general less problematic.

In humid areas, synthetic underlayments are often a better choice because they’re impermeable to water. Moisture won’t seep through to the roof deck, which means these underlayments will prevent damage from wind-driven rain, ice dams, and water pooling on the rough. Additionally, these types of underlayments are usually sturdier, designed with multiple layers of polyethylene or polypropylene, which makes them strong enough to stand up to the weight of metal and less likely to tear during installation.

Choosing the Right Epilay Underlayment

Epilay’s underlayments come in several grades, from Protectite Platinum, which features 17 MIL thickness, all the way to Protectite Superior, which is a 7 MIL underlayment. There is also Protectite Plasfelt, which is our lightest underlayment, but still comes with superior tear strength to traditional felt underlayments. All of the products in the Protectite line are water repellent and non-absorbent, and all of them are rated to work well with metal roofing systems. The choice comes down to two things. Local building codes will be the primary consideration, so make sure to choose the right thickness that meets area standards. The other consideration will be the intended life of the roof. You’ll want to choose an underlayment that matches the rooftop’s expected lifespan to maximize the roof’s longevity. Each of Epilay’s products comes with a limited warranty, from ten years for Plasfelt all the way up to forty years for Protectite Platinum.

And there you have it! Synthetic underlayment is the ideal choice for a metal roofing system. Choose the thickness that fits with area building codes and will stand up to metal’s long lifespan to create a solid roofing system that will protect the rest of the home against water damage.