A new asphalt-saturated, high-performance polyester (HPP) underlayment can be used under a variety of primary roofs, including metal, shingles, and tile. (PHOTOGRAPH COURTESY OF TARCO ROOFING)

Five industry experts — Arturo Horta, roofing manager, DuPont Building Innovations; Fernando Mesa, vice president of sales, Polyglass USA; Frederick J. O'Connor, corporate director of technical Systems, Tamko Building Products Inc.; Steve Payne, market development manager, construction products, Johns Manville; and Steve A. Ratcliff, president and CEO, Tarco Roofing — discuss the state of metal roofing underlayment:

Q: Are the self-adhered products taking over from the old nailed underlayment?

Horta

Horta: No. Self-adhered products have very limited usage in metal roofing. These types of products are only used in northern climates when required by code and only cover a small section of the roof, such as eaves and valleys. Product cost and labor to install them are the major issues of these self-adhered products. Mechanically fastened roofing underlayments, secured to roof sheathing with nails or staples, are still the preferred choice of roofers, roofing contractors, and the metal roofing industry in general.

Payne

Payne: They are not taking over, but self-adhered and hybrid-material (asphalt and nonwoven polyester) products are definitely becoming more prevalent — with good reason. One of the biggest benefits of self-adhered underlayment is its resistance to the effects of wind-driven rain and ice dams. Water backing up at the eaves and rakes can find its way through the seams of conventional felt far more easily than it can with a self-sealing underlayment. In most parts of the country, though, mechanically attached hybrid-material underlayments are more than adequate, as well as less expensive. They're less prone than felt to buckling and weather damage before the roof goes on and are more resistant to mold and mildew growth.

Mesa

Mesa: Self-adhesive underlayments continue to grow in popularity and in many instances are the standard for metal roofing applications. Reasons for the growing popularity of self-adhesive products include ease and speed of installation, reduced labor costs, reduced material costs for fasteners, and, of course, increased staying power during high-wind weather events. Many self-adhesive underlayments also feature a self-healing property that provides sealability to fasteners that penetrate them during the installation of the finished roofing system.

O'Connor

O'Connor: Organic underlayment remains very popular, especially considering self-adhered underlayment has been on the market for more than 20 years. Both products are of good service in roofing construction, depending on the nature of the project. "Taking over" would be overstating the reality, given the time of market entry and higher cost of self-adhered products. With organic felt playing a major role as an underlayment installed in the field of the roof area, self-adhered underlayment has historically worked at critical points on the roof, such as eaves, rake edges, penetrations, and dormers. Use of self-adhered over the entire roof is expanding; however, consideration must be given by the design professional with respect to proper ventilation. There is a considerable amount of building code activity involving self-adhered underlayments. Depending on code evolution with respect to roofing underlayments, self-adhered use could very well expand.