Synthetic vs. Felt Roofing Underlayment

When you think of a roof, you probably count shingles or metal as the main component. Did you know there’s another, less well known layer of protection? It’s called underlayment, and as it turns out, it’s important stuff. Its biggest function is preventing moisture damage.

What Is This, Anyway?

Roofing underlayment is situated between the shingles and the roof deck (the latter is typically made from plywood or OSB). It’s installed directly on the roof deck. Its function is to provide a secondary layer of protection against the elements – rain, snow, high winds, stuff like that.

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The Options Are…

When it comes to types, roofing underlayment is pretty simple. You have felt, you have synthetic, and there are a few side types that aren’t used very often, so we aren’t covering them here.
Each type has positives and negatives. Which of these you choose often depends on where you are (i.e. local environment, climate, and similar), what roofing materials you’re using, the design of your roof, your budget, and what your roofing contractor suggests. If you haven’t decided on a contractor yet (perhaps you’re reading ahead to stay informed – good for you!), we at 1OAK Roofing would be glad to get you started.

Felt Underlayment

Felt is one of the oldest underlayments. It typically costs less than synthetic, making it a good choice for people with tight budgets; this is its main advantage. Unfortunately, it does have a few downsides.
One drawback is that it often can’t be left exposed for more than a few hours, as this can compromise its moisture-protection ability. Felt underlayment can tear during high winds and during installation. It’s available in two kinds – No. 15 and No. 30 – and the latter is less likely to tear, being thicker. During initial installation, felt underlayment can wrinkle if exposed to moisture, meaning that the shingles should typically be installed immediately afterward for minimum problems. Felt underlayment weighs more than synthetic, which makes it trickier to get onto a roof, and the weight means it has less material per roll, causing more seams. It’s also somewhat slippery, which can make installing it a hassle.
Felt is not exactly the best underlayment out there, but if you have a tight budget, it might be your thing.

Synthetic Underlayment

Synthetic is a newer arrival on the roofing scene. Its biggest disadvantages are the following:
Synthetic underlayment isn’t standardized and may be made from different materials depending on the manufacturer. Do your research when selecting this type. It also costs quite a bit more than felt does.
Its advantages are its toughness, its installation speed (it’s faster than felt since it weighs less), its safety for the workers installing it, and its ability to repel water, instead of absorbing it.

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