Polypropylene Roof Underlayments

Benefits

• Compared to felt underlayments, synthetic underlayments offer greater protection against tearing, moisture, rain, wind and ultraviolet rays. They provide up to six months of weather-barrier protection, which makes them extremely useful in emergencies and for delays in new home construction. Polypropylene roof underlayments weigh less than felt underlayments. Some polypropylene roof underlayments are available with slip-resistant and fire-resistant properties. At first glance, the cost is prohibitive. Polypropylene roof underlayments can be as much as 30 percent higher than felt paper, according to the National Association of Home Builders. However, the initial cost may be offset by lower labor costs.

Installation

• Polypropylene roof underlayments are recommended for high-slope installations. The installation process is relatively simple. The lighter weight of the material makes it easier to handle than felt. The material is applied along the bottom edge first, parallel to the overhang eave. End and edge laps vary depending on roof style. The exact layout and overhang requirements may differ by manufacturer. Polypropylene roof underlayments are attached with roofing nails, although in high wind areas plastic caps may be needed.

Quality Control

• Quality control measures for polypropylene roof underlayments are set forth by the International Building Code with evaluation reports on specific products issued by the ICC Evaluation Service. Manufacturers are required to have a documented quality control program for underlayments, with the program administered by an inspection agency accredited by the International Accreditation Service, Inc.

Disadvantages

• Polypropylene roof underlayments are relatively new, and therefore still subject to a learning curve. The underlayment can cause problems if it is not installed improperly. For example, polypropylene roof underlayments are not self-sealing, so installing the material with staples compromises the moisture resistance of the material. In 2010, the National Roofing Contractors Association voiced several concerns about synthetic underlayments. One concern was a lack of ASTM (American Society for Testing and Materials) standards. Another was apprehension that the underlayments might void manufacturers’ material warranties for some shingle types. Third, the NRCA noted some brands of synthetic underlayments did not meet current code requirements.