Beefing Up Low Slope Roofing Installation

02/07/2011 | By Richard L. Fricklas

Beefing Up Low Slope Roofing Installation

With commercial construction at low ebb, innovation has generally focused on gathering financial incentives for installing PV systems or vegetated roofs.

Though the low slope roofing industry has essentially stabilized, the methods of installation have evolved. Reasons for innovation include compliance with more restrictive environmental issues, such as volatile organic compounds (VOC), the ability to recycle, enhanced reflectivity (albedo) and/or emissivity, and cleaner and quieter application techniques.

Much credit for the changes should go to the Roofing Committee on Weather Issues (RICOWI), whose field teams traveled to the sites of hurricanes and reported on needed improvements in wind resistance. Credit also goes to work directed by Dr. Bas A. Baskaran, group leader of the Performance of Roofing Systems and Insulation subprogram at the Institute for Research in Construction, part of the National Research Council of Canada in Ottawa.

The State of the Industry
For now, the low slope roofing industry is holding steady at five categories:

1. Conventional bituminous build-up roofing (BUR)
2. Polymer-modified bituminous roofing (MB)
3. Single-ply polymeric roofing, especially PVC and TPO
4. Hydrostatic (low slope) metal roofing
5. Sprayed in place polyurethane foam and associated surfacing

As for the beef, requirements for thermal insulation have grown from low thermal resistance products such as wood fiber, perlite, glass fiber, and foamed glass with R values of less than 3 per inch, to Rs of 5 per inch or more. (R values are reported in resistance units, e.g., hours that it takes a Btu to travel from the warm side of a construction to the cold side.) These early products were fine for bridging the rib openings of a steel deck and were efficient enough while energy was cheap. By the time of the oil embargo of 1973-1974, concerns were raised that R values of 3 were inadequate. The crisis called for serious energy conservation.

In the next (and current) generation, cellular plastic foams began to replace the low R materials. A number of composite products hit the market to beef up deficiencies in an all-foam material. One issue was fire resistance. Foam plastics applied directly to a steel deck could not meet requirements for resistance to an under-deck fire. One composite consisted of a base layer of fire-resistant perlite-board, a core of urethane foam, and a top facer or asphalt-saturated roofing felt. Another used a fiberglass base. Both complied with requirements. Another successful innovation was to mechanically attach gypsum board (usually 1/2 inch thick) to a steel deck, followed by the urethane or isoboards.

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