The best weight for roofing felt is the 30 pound product, because it provides a thicker and stronger base for roofers that won't shed, especially on steep roofs where foundation is critical. Most roofing contractors prefer to use synthetic felt because of its various advantages in terms of strength, weight, safety, and cost. However, not all roof types are compatible with synthetic felt, and in that case, most will suggest opting for a 30-pound felt if you can afford it. Heavy-duty roofing felt is available in 15 and 30 pound weights.
The 30-pound product is the best weight for roofing felt because it provides a thicker, stronger base for roofers that won't shed, especially on steep roofs. Roofing experts have found that adding a layer of protection between the structural roof covering (the layer of wood that covers the joists) and the roof shingles helps create a more attractive and durable roof. Lighter, thinner rolls mean more square coverage per roll, resulting in fewer trips up a ladder for roofers. Divide the area of your roof by the area of the felt rolls you plan to use and allow approximately an additional 10% for waste.
You may hear some say: “If the felt paper is nailed, it basically spoils or cannot be applied as a waterproofing agent. For more than 25 years, organizations such as the National Association of Roofing Contractors (NRCA) and the Canadian Asphalt Shingle Manufacturers Association (CASMA) have included roofing felt in their roofing and waterproofing recommendations. Finally, the permeability indices of synthetic underlayment may be less than 0.1, which makes synthetics essentially impermeable vapor barriers. In addition, on steeper roof slopes, 30-pound felt paper is needed for the installer's anti-slip protection, and is also less likely to break during shingle installation.
However, roofing felt does not offer the lowest moisture permeability characteristics of synthetic underlayment. This protects the wood from damage and essentially gives you a better looking and more durable roof. No matter what residential roofing project you are undertaking, in the words of the Canadian Asphalt Shingle Manufacturers Association, using a felt or synthetic underlayment simply makes “good roofing sense.” It can also increase your home's fire rating and provide roofers with slip protection when installing shingles. Read on to understand the purpose of roofing felt paper and how this product will add an integral layer of protection to your roof and residence.
Conversely, the 15-pound felt can break, leaving the underlying roof structures unprotected. Roofers may consider adding layers of underlayment for superior protection, which is especially useful on low-slope roofs. Also known as tar paper, this first underlayment proved to be an effective and economical roofing solution for decades, giving roofing covers a secondary layer of water protection against the damaging effects of the elements.