Roofers are faced with all kinds of choices as they design and install new roofing systems. One of those choices is the type of underlayment to be installed beneath the roofing itself. It should be a water-resistant barrier that acts as a secondary line of defense against moisture infiltration. In some cases—after severe weather, for example—some underlayments can even serve as a barrier against moisture damage while waiting for repairs or the installation of a new roof.
These days, there are three different types of underlayment out there. Asphalt saturated felt has been around the longest, which makes it a popular choice because roofers are familiar with it. But there is also rubberized asphalt and non-bitumen synthetic underlayment, too. Let’s take a look at each of the three along with their advantages and disadvantages.
Asphalt Saturated Felt Underlayment
Asphalt saturated felt has been on the market a long time. This is a paper product that is saturated in crude oil byproducts to help protect the paper itself against water. It comes in 15-pound and 30-pound thicknesses with the 30-pound felt being the thicker of the two.
This type of underlayment isn’t completely impervious to water, but it is considered water resistant. In particular, 30-pound felt is more resistant than 15-pound, which means it’ll give the roof a bit more protection.
There are a few common failure points to watch for when installing asphalt saturated felt:
- It’s not resistant to UV damage, which means that when installing it, it must be covered by the primary roofing material immediately.
- Because felt tears easily, it is easily damaged during installation. You’ll need to take care when installing fasteners or walking across it.
- Over time, it doesn’t last as long as other underlayments because the volatile compounds that make it water resistant dissipate. This is particularly true in warmer environments.
Rubberized Asphalt Underlayment
Rubberized asphalt can refer to a variety of underlayments that all have one thing in common: They have a rubber-like look and feel to them. Most of these products are a peel-and-stick underlayment, which means that instead of requiring fasteners, installers need only peel off the membrane to adhere them to the roof. Because they’re peel-and-stick, most of these products will self-seal around nails and staples.
These underlayments work very well to protect a roofing system against water damage, and they’re more heat resistant than asphalt saturated felt, too, which means they’ll last longer once installed. Additionally, in situations where roofers may need to wait a bit before installing the primary roof covering, rubberized asphalt can usually be left exposed to the elements for between 90 to 180 days.
The drawback to these underlayments is the cost. For the added benefits, you’re likely to pay more than you would for asphalt saturated felt.
Non-Bitumen Synthetic Underlayment
Synthetic underlayments differ from the other two types in that they don’t include asphalt or rubber. Instead, these are generally made from polyethylene or polypropylene polymers. In comparison to asphalt underlayments, synthetics are much lighter and have much high wind resistance and tear strength. There won’t be an issue with asphalt degrading over time, and these products, because of their lighter weight and resilience, are typically easier to install, too. Most synthetic underlayments are also highly resistant to UV rays, which makes them ideal for situations in which the roof may need to be left uncovered. For instance, Epilay’s underlayments feature up to a year’s UV protection.
The drawback? Cost may be an issue—this is one of the more expensive underlayment types on the market. However, ease of installation and a long use life offsets this. You may also need to check with the supplier for your primary roofing material because in some instances, certain types of roofing may require a specific underlayment beneath in order to meet warranty requirements.
A good underlayment is a vital part of any roofing system, and there are lots of different options to consider. Weather, moisture resistance, the area’s climate, local building codes, and the requirements for the roofing product that you’ll be using—these are all things you’ll need to factor in order to choose the perfect underlayment!