47.5 MB - The Whole Building Design Guide

Loads and Attachment Methods 9Information on loads on rooftop equipment was first introducedin the 2002 edition of ASCE 7. For guidance on load calculations,see “Calculating Wind Loads and Anchorage Requirements forRooftop Equipment” (ASHRAE, 2006). A minimum safety factorof 3 is recommended for critical facilities. Loads and resistanceshould also be calculated for heavy pieces of equipment since thedead load of the equipment is often inadequate to resist the designwind load. The 30’ x 10’ x 8’ 18,000-pound HVAC unit shownin Figure 3-69 was attached to its curb with 16 straps (one screwper strap). Although the wind speeds were estimatedto be only 85 to 95 miles per hour(peak gust), the HVAC unit blew off the medicaloffice building.To anchor fans, small HVAC units, and reliefair hoods, the minimum attachmentschedule provided in Table 3-2 is recommended.The attachment of the curb to theroof deck also needs to be designed and constructedto resist the design loads.Mechanical penetrations through theelevator penthouse roof and walls mustpossess adequate wind and waterresistance to ensure continuity of elevatorservice (see Section 3.3.3.3). In additionto paying special attention to equipmentattachment, air intakes and exhaustsshould be designed and constructed toprevent wind-driven water from enteringthe penthouse.Figure 3-69:Although this 18,000-pound HVAC unit wasattached to its curb with16 straps, it blew offduring Hurricane Ivan.(Florida, 2004)9. Discussion is based on: Attachment of Rooftop Equipment in High-wind Regions—Hurricane Katrina Recovery Advisory (May 2006,revised July 2006)MAKING CRITICAL FACILITIES SAFE FROM High Wind3-83