Roofing felt has been around for a long time. More than 170 years ago, prospectors covered their shanty roofs with roofing felt, which was known as felt paper or tar paper back then. And it served as the primary roofing material, too, not just an underlayment. Technology evolved over the years, and roofing felt changed, becoming an underlayment beneath shingles and other types of roofing. And technology continues to evolve, which is why we now have synthetic underlayments that are even better than old-fashioned roofing felt.
What makes synthetic underlayment better? Read below and you’ll find all the facts you need to know!
The Difference Between Roofing Felt and Synthetic Underlayment
Though they serve the same purpose, these two are very different products. Roofing felt is usually made with either polyester or fiberglass fleece. To waterproof it, it’s soaked in chemicals and tar. It comes in 15 pound and 30-pound thicknesses, which are references to how much a 100 square foot roll of roofing felt used to weigh depending on its thickness.
Synthetic underlayment is typically made from woven or spun polyethylene or polypropylene, and it comes in a variety of different thicknesses to suit your needs. These typically weigh a lot less than traditional roofing felt, and many products have layered design. ProtecTite Platinum, for example, features a bottom anti-skid layer followed by a layer of cross-woven scrim, a bonding layer, and then a top non-woven layer featuring a cool surface and GripWalk for enhanced walkability. Materials and design mean that synthetic underlayment is not only lighter than traditional roofing felt, but also much tougher, plus it comes with added features like anti-skid upper and lower layers to make installation and traction easier.
Length, Width and Weight
Another advantage to synthetic underlayment is that there is more material per roll. They’re typically four feet wide, which means they cover about 1,000 square feet of roofing deck. This contrasts to traditional felt rolls, which are normally three feet wide and cover about 400 square feet.
This is one of those advantages that is often understated. Synthetic underlayment is lighter, and the rolls cover more of the rooftop, which means it’s much easier and faster to install and it requires fewer trips up and down ladders to get it on the roof.
How much lighter is synthetic underlayment compared to roofing felt? On average, synthetics weigh about 23 pounds per 10 square feet of material whereas for the same coverage, roofing felt weighs 130 pounds.
Differences in Permeability
Most synthetic underlayments are much less permeable than traditional roofing felt. This means a couple of things. First, because of this, synthetics tend to be more water resistant—and some, like peel and stick underlayment, can be waterproof. In contrast, roofing felt acts as a moisture barrier, but may not be completely waterproof.
The other thing to be aware of where permeability is concerned is that traditional roofing felt will allow the roof to breathe a little bit, which means that moisture in the attic will escape slowly through the felt. Because synthetics are more impermeable, attic moisture can’t escape—and that means proper ventilation in the attic is essential.
Synthetic Offers Easier Installation
The lighter weight and higher coverage isn’t the only reason why synthetic underlayment is easier to install. It’s also less prone to tearing or wrinkling, and when fastened in place properly, it’ll stay in place against wind whereas felt may lift. This means less hassle before the roof goes on.
Again, specialized surfacing on synthetic underlayments help, too. As mentioned above, Epilay’s GripWalk surface safeguards against slips and falls. Synthetics also have cooler surfaces that absorb less heat than traditional felt—and as roofers know, anything that cuts the heat while roofing on a hot summer day makes the job easier!
With that, synthetic underlayment also performs better in cold weather. Tar in roofing felt underlayment makes it stiff when the weather gets chilly, which makes it harder to work with and more prone to cracking. Synthetics are just as flexible in cold weather as in warm.
Synthetic underlayments can be a little more costly—though thinner synthetic underlayment is usually comparable in price to a quality felt product—but the advantages to synthetic underlayment are clear. It’s a durable product that offers better protection, easier installation, and increased safety for those who are installing it. And that is why so many roofers are breaking with tradition and instead using modern synthetic underlayments on their roofing products!
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