Today’s photovoltaic (PV) industry must rely on licensed structural engineers’ various interpretations of building codes and standards to design PV mounting systems that will withstand wind-induced loads. This is a problem, because–although permitting agencies require assessments of the structural attachment of solar equipment to rooftops—the safety and sufficiency of these attachments are not adequately addressed in any codes or standards. The result is a multitude of code interpretations from a range of individuals and groups, often yielding different design loads for the same design specifications.
Solar America Board for Codes and Standards Recommendation
- At present, they recommend basing the structural design of roof-mounted PV systems on the ASCE Standard 7-05 as follows:
- Section 18.104.22.168, main wind-force resisting system (MWFRS), is the recommended starting point for designing the PV mounting structure, with the PV module oriented above and parallel to the roof surface.
- Section 22.214.171.124.1 addresses wind loads on components and cladding. We recommend the use of Section 126.96.36.199.1 and supporting Figures only for the design of the PV module attachment clips and hardware to the structure, and for calculating loads on individual PV modules.
- We do not recommend Section 6.5.15, 188.8.131.52, and Figure 6-21 for the design of PV systems.
- This report provides basic guidance for applying ASCE Standard 7-05 to existing codes and standards for the typical residential application of PV arrays mounted parallel to the roof slope and relatively close (3 to 6 inches) to the roof surface.
- They recommend wind tunnel testing be conducted for the most common rooftop PV installations to verify methods and calculations. The installation types include standoff mounting parallel to the roof, stand-off mounting at an incline relative to the roof, and ballasted installations on flat roofs.
- They recommend that codes and standards be modified to specifically address the mounting of PV arrays to rooftops to eliminate potential barriers to market development in high wind regions.
- They recommend that local jurisdictions and design professionals use the recommendations in this report to ensure continuity in interpreting existing codes and standards.