You don't have to understand every aspect of roof construction to understand the purpose of an underlayment. Roofs involve a layer of plywood to support your shingles and add rigidity, and in between that decking and the shingles there is a third layer of material known as underlayment. It's designed mainly to stop moisture that manages to make it past the shingles, and basic asphalt-soaked felt was the primary option for decades. Find out why this material is on its way out as synthetic underlayments replace it.

Limited Supply

First, asphalt products in general are being phased out in many industries because asphalt is not as widely available or as affordable as it once was. Asphalt is generally produced as a byproduct of crude oil refinement to make gasoline and other products. As the process advanced, these byproducts became rarer. While asphalt roofing felt was once a good way to use up a byproduct available at a low cost, now supplies are limited and it's simply not worth making roofing felts for many manufacturers. Other underlayment products either use asphalt in limited quantities or none at all.

Low Water Resistance

Asphalt-impregnated felt does resist moisture to a certain amount, but not as much as you might think, since it's installed on so many millions of roofs. Water doesn't usually travel past the shingles above unless they're damaged or missing, so standard felt is only designed to capture a little moisture and dry out again after the storm passes. In contrast, most synthetic underlayment products offer far more water resistance. Some are even rated as waterproof so that missing shingles won't even cause the plywood decking to get damp. For the longest-lasting roof, waterproof materials are better than ones that are only water resistant.

Insufficient UV Protection

The underlayment on your roof protects it from more than just moisture. Sun exposure has a surprisingly detrimental effect on the plywood that forms the decking of your roof. When a shingle goes missing or many of them curl up at the edges, this lets light through to speed up the breakdown of the wood and formation of a serious roof leak. Old-fashioned asphalt roofing felt has limited UV protection, but modern synthetic options are a lot more resistant to the effects of sunlight. This means that the roof can stay uncovered longer during the assembly process as well.

Wrinkling and Crumpling

Have you ever noticed that a neighbor's roof looks almost wrinkled or rippled, even if it's brand new? This is an effect caused by the asphalt felt below buckling as it absorbs moisture, which can come from humid air alone if the shingles are still intact. Heavy-duty shingles will stay straight and even on top, but thinner and lighter shingles tend to move with the felt and will show the effects at the surface. While this buckling is minor and doesn't affect the health of the roof in most cases, it can create gaps that let water in when the wrinkling is bad enough. Synthetic underlayments tend to have adhesive backings to prevent this, and their water resistance also helps prevent buckling.

Heavy Weight

Finally, asphalt felt tends to weigh more than the more modern rubberized materials. This is rarely a problem for roof structural considerations, but it does slow down installation and wears out the crew handling the installation. It also adds up over the years if you plan to have your roof covered with new layers of felt and shingles rather than stripped off and replaced from the bottom up. Lighter underlayments keep the total weight down as you add on the new layers.

To learn more about roofing, check out websites like http://www.skerlec.com.