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When it comes to roofing, underlayments, and roofing ventilation systems, there are a lot of misconceptions floating around. A big one is that your underlayment needs to be “breathable” in order to let your roof ventilate itself properly.

That’s a myth that isn’t exactly true—and we’re going to show you why, plus clear up some other misconceptions.

The Real Advantages of Synthetic Roofing Underlayment

People ask all the time whether synthetic underlayment is “breathable,” and the answer is that no, it isn’t—and it isn’t supposed to be. Actually, that’s one of the big advantages of synthetic underlayments like Epilay Protectite. These products are designed to be impermeable to moisture, which makes them impermeable to air, too.

That’s a good thing because it means that moisture and humidity will have a tough time seeping through the underlayment, where it can cause mildew, mold, and rot. In fact, when you use a peel-and-stick underlayment like EpiStik Plus, you can use it to create a completely watertight roofing system since the adhesive will seal along laps and around fasteners.

That’s as opposed to underlayments like traditional roofing felt. Roofing felt will stop some moisture from reaching the roof deck, but not all of it—and worse, it performs poorly when exposed directly to moisture, which means that when you use it, the underlayment needs to be covered immediately with shingles or another roofing material.

In the wake of a damaging storm, that can prove disastrous since roofers may not have time to visit every home to fix every roof. It means you’ll have to tarp the roof and hope for the best until contractors have a chance to make repairs. Meanwhile, with synthetic underlayment, this isn’t a concern since it’s not only engineered to perform well against moisture but also to withstand UV exposure for weeks or even months if needed.

So How Do You Ventilate a Roof Properly?

In most cases, properly venting a roof has little to do with underlayment or your primary roofing material. Rather, it means actually installing vents in the building’s attic so that fresh air can flow in, and hot, moist air can flow out. These often come in the form of gable vents, soffit vents, and ridge vents, all of which can help ensure good airflow.

Do You Ever Need Breathable Underlayment?

There are a few rare situations where you may want a breathable underlayment. These include flat roofs or low-sloped roofs where moisture can pool and areas that experience extreme humidity. In these instances, your roofing system should either be completely watertight to prevent seepage through to the roof deck—or the underlayment should be breathable so that the roof deck is better able to dry out.

The Most Important Factor: Professional Installation

Whether building a new home or reroofing an existing home, the most important part of creating a properly ventilated roofing system is professional installation. Experienced roofing contractors will know how to best protect a roofing system against moisture, and they should understand how to create a properly ventilated roof that protects the whole home. That kind of experience plus the durability and moisture resistance of Epilay underlayment will ensure that your roof will perform well against the elements.

In Summary

The idea that underlayment needs to be breathable so that a roof can be properly ventilated is a myth—except in certain rare cases where water may be prone to pooling on the rooftop. Barring that type of situation, it’s typically much better to go with a non-breathable synthetic underlayment to create a roofing system that keeps water out.