Roofing Codes: Wind Resistance of Low-Slope Roof Systems
February 9, 2006
Chapter 15: Roofs and Roof StructuresSection 1505.2 - Wind Resistance of Low- Slope Roof Systems
The low-slope roof systems described in Section 1507.5 which are mechanically attached, adhered to the roof deck or ballasted shall be designed to resist the design wind load pressures of Section 1609.0. Roof systems with built-up, modified bitumen, fully adhered or mechanically attached single-ply, metal panels, and other types of membrane roof coverings shall also be tested in accordance with FM 4450, FM 4470, UL 580 or UL 1897 listed in Chapter 35.
This code implies that all low-slope roof systems should be designed and installed to meet wind resistance requirements. Wind resistance for roof systems is primarily wind uplift resistance. Section 1609.0 (referenced in the code) states that “All buildings, other exposed structures, components, cladding and roof coverings shall be designed to resist the pressures caused by wind in any direction as provided for herein.” The provisions and formulations provided in Section 1609.0 are identical to formulations used by ASCE and Factory Mutual. The section provides the required reference material to determine wind uplift resistance for specific structures. The procedure to determine roof wind uplift classifications on specific buildings during the design phase is based a calculation that takes into account the basic wind speed in the geographical area, ground surrounding the building and the roof uplift pressure at the field of the roof. The building’s height and perimeter construction are also considered. It is the responsibility of the specifier to complete these calculations. It is the specifier’s responsibility to determine the proper wind uplift classification for the building.
The code also states the all applied roof materials shall be tested and approved for use by FM (Factory Mutual) and UL (Underwriters Laboratories). Required FM testing is in accordance with their standard 4450-90 Approval Standard for Class I Insulated Steel Deck Roofs and 4470–86 Approval Standard for Class I Roof Coverings. The required UL testing is standard 580-94 Test for Uplift Resistance of Roof Assemblies. This provides a departure from conventional thinking that only Factory Mutual Insured properties must meet their wind uplift and testing standards.