The earliest use of felt, or tar paper, dates back to the California Gold Rush. In the time since temporary shacks in California, felt paper’s use and manufacturing methods have evolved into several different types of underlayment that are required for building codes and roofing warranties.
Felt paper’s purpose is not to make the roof waterproof. In fact, the purpose of an underlayment is to protect the wood sheathing from any condensed moisture on the underside of the shingles. Basically, if no underlayment or felt was used the wood decking would warp and be damaged. Today, manufacturers produce several different kinds of underlayment, giving contractors and homeowner’s options.
The industry standard for many years, felt allows air to pass through, thus making the roofing system function as it should. Most residential tear off and re-shingle jobs take only a day or two. So the standard, inexpensive 15 lb felt, is only exposed to elements a short time.
It sounds better than 15 lb felt to many, at twice the cost. Though still inexpensive compared to some new synthetic materials, 30 lb felt will allow less air flow than 15lb. But some just prefer the idea of a heavier felt underlayment.
Newer synthetic materials, such as Rhino, are used by contractors because “new” sounds better, relatively cheap product, faster to install and easier to walk on than traditional felt paper. The product will not curl or ripple if left exposed to the elements like felt can. However, most synthetic underlayments are impermeable. They do not let air pass through, making the importance of proper attic ventilation more of a factor. Soffit vents clear of insulation and the proper amount of roof vents is important on every roof. When using these brands of synthetic, correct venting will prevent premature deterioration of your asphalt shingles.
GAF Deck Armor is one of the only breathable synthetic underlayments. Others such as Owens Corning Deck Defense and Titanium are not permeable, but offer the exceptional strength and protect homes from wind driven rains. These high end underlayments are significantly more expensive. If you are going to re-roof your home, these products would not be recommended. However, if you are building a new construction home, the extra cost is worth the protection that these premium products offer.
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