Retrofit Single-Ply Roof Systems: An Assessment of Wind Resistance James R. Kirby, AIA, Building and Roofing Science Architect, GAF
Metal buildings with metal panel roof systems are commonly used across the United States for storage and commercial office space. A retrofit single-ply roof system (RSPRS) is often installed on top of the metal panel roof after it has been determined that the metal roof no longer provides useful service. Before jumping into the discussion about retrofit single-ply installations, it’s necessary to mention that there are generally four ways to replace or re-cover an existing metal panel roof system.
A retrofit single-ply roof system over a metal roof can be installed in one of the following ways: ■ The membrane can be mechanically attached into the substructure
■ Metal roof panels can replace the existing metal panels, or they can be installed as a re-cover roof system. ■ Single-ply roof systems can be installed as a re-cover roof system. ■ Roof coatings can be applied to the existing metal roof. ■ Spray polyurethane foam can be installed over the existing metal roof. The focus of this article is the use of single-ply roof systems as re-covers over existing metal panel roofs.
Attachment Options
(i.e., the purlins) through the insulation layer. This is generally considered to be best practice. ■ The membrane can be adhered to insulation that is mechanically attached to the metal roof panels. This can be problematic because the metal roof panels are not equivalent to a steel deck. ■ The membrane can be adhered to insulation that is adhered to the metal roof panels. This could be problematic for long-term performance.
The method of attachment for a retrofit single-ply roof system over an existing metal panel roof is of Membrane Adhered to Mechanically utmost importance for the long-term success of the Attached Insulation overall roof system and for the wind-uplift resisWhile it is possible to use an adhered membrane tance of the single-ply system. over mechanically attached insulation into existing 22
FLORIDA ROOFING | March 2020