Are there any wind-related building code requirements or design standards pertaining to the attachment of rooftop equipment?

Rooftop equipment is typically torn off in high winds because equipment anchorage to the roof is inadequate, the strength of the equipment is inadequate, or the equipment is corroded. FEMA P-55, Coastal Construction Manual (FEMA 2011), includes prescriptive attachment recommendations for small equipment (see Section 12.8.2.1). Such equipment may include exhaust fans, vent hoods, and some residential air conditioning units. FEMA P-55 also provides guidance on job-site strengthening of fan hoods and cowlings through the use of stainless steel cables.

If the mounted equipment is more than 30 inches above the curb, the attachment design should be based on the calculated wind loads from ASCE 7-10, Minimum Design Loads for Buildings and Other Structures. Chapter 29 of ASCE 7-10 contains provisions for determining the lateral force and vertical uplift force on rooftop equipment for buildings with a mean roof height less than or equal to 60 feet. Figure 29.5-1 of ASCE 7-10 provides a force coefficient for chimneys, tanks, rooftop equipment, and similar structures. The force coefficient, Cf, is applied to equations found in Section 29.5.1 of ASCE 7-10 to calculate both the lateral and uplift design wind forces. The lateral force is based on the vertical area of the equipment as projected on a vertical plane perpendicular to the direction of the wind. The uplift force is based on the horizontal area of the equipment as projected on the horizontal plane above the equipment and parallel to the direction of the wind.

To avoid corrosion problems, FEMA P-55 (Section 12.8.2.1) recommends nonferrous metals, stainless steel, or steel with a minimum G-90 hot-dip galvanized coating for the equipment itself, equipment stands, and equipment anchors when located within 3,000 feet of a body of water producing salt spray. Stainless steel fasteners are also recommended.

References:

• ASCE. 2010. Minimum Design Loads for Buildings and Other Structures. ASCE 7-10, Reston, VA, May 2010.
• FEMA. 2011. Coastal Construction Manual. Washington, DC. FEMA P-55. August 2011.