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Gravity Design For Rooftop Solar Photovoltaic Arrays PV3-2019

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SEAOC is pleased to announce the publication of “Gravity Design for Rooftop Solar Photovoltaic Arrays” (SEAOC PV3), developed by the SEAOC Solar Photovoltaic Systems Committee. PV3 is the third in a series of publications by the SEAOC PV Committee, following previous recommendations related to seismic design of rooftop solar arrays (PV1, 2012) and wind design (PV2, 2012, updated 2017). The PV committee was formed in September 2011 with the goal of addressing the lack of specific requirements in applying structural building code provisions to solar photovoltaic systems. SEAOC’s work on PV1 and PV2 helped lay the groundwork for new provisions on these topics in ASCE 7-16.

The PV3 report addresses key issues for evaluating the capacity of building roof structures to support gravity loads imposed on them by PV arrays, including:

  • Whether PV systems arrays should be considered as dead load or live load.
  • Conditions where roof live loads would not reasonably occur in conjunction with rooftop PV installations and where they could be reduced or eliminated from consideration to offset the additional dead load of PV systems.
  • Associated appropriate assumptions for tributary area for live load area reductions in conjunction with PV systems.
  • Considerations regarding PV systems supported on open grid framing.
  • Rain loads and ponding.
  • Seismic considerations regarding addition of PV dead load.
  • Snow load and drifts.
  • Solar-ready roof areas.

 
The report further addresses the following considerations related to adding PV systems to existing buildings, including:

  • Need to check for load case where PV panels are not added or present on an existing roof.
  • The need to apply the 300-pound concentrated roof live loads for maintenance workers -- a relatively new design requirement for which many older structures were not designed.
  • Interpretation of the upgrade trigger associated with increasing gravity loads, specifically regarding use of live load offset to justify addition of PV dead load.
  • Determination of allowable stresses for older wood structures.
  • Computation of deflection, deflection limits, drainage and ponding, and protection of architectural elements when adding long-term dead load to an existing structure.
  • Verification of existing conditions prior to adding dead load.