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RE: Wind load design for Photovoltaic panel installations

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I've been cutting my teeth on the new codes and realize how much I have to learn.  My opinion is that you would use the ASCE provisions for monoslope free roofs or solid signs, whichever is more applicable to you actual situation.  But to further complicate things, for something on a roof, should you figure the topographic factor as if the building below the solar panels was an escarpment itself?  The more I learn the new codes the questionier I get.


Bob Garner, S.E.


From: Dennis Wish [mailto:dennis.wish(--nospam--at)]
Sent: Wednesday, August 13, 2008 1:04 AM
To: seaint(--nospam--at)
Subject: Wind load design for Photovoltaic panel installations


Can anyone guide me to the section of the ASCE 7-05 that I would need to use to design the wind load conditions for contractors and distributers who are retrofitting solar electrical panels onto existing roofs? I would consider the component to be open from the bottom and would need to find the design section in the current IBC 2006 and ASCE 7-05 for wind design acting upward on the panels as well as the resultant wind force acting downward on the panels based on the slope of the roof and the geographic location or the building departments requirements for local wind speed and wind category.


Can anyone get me started? I think the problem is going to narrow down to checking the existing roof capacity for the additional downward and upward force of wind plus the weight of the panels and their means of connecting to the roof. In areas where the roof is designed using metal plate wood trusses there is going to be a potential problem with proving the retrofit weight of the panels on systems that are traditionally designed only for the weight of the materials original to the design of the home. At least two local contractors have contacted me about this problem since the local building departments are requiring a design by a local engineer to assure the capability of the roof to carry the additional load and the potential for uplift that could dislodge the panels from the roof – tearing the roof away with the panel mountings.


Has anyone worked on this type of problem since the adoption of the new code in January? If possible, please reply to me privately (unless others are interested in this type of problem for their area) as I need to decide whether or not to take on this type of work assignment considering the potential liability of the wind effect under the new code on an existing roof.





Dennis S. Wish, PE


Dennis S. Wish, PE

California Professional Engineer

Structural Engineering Consultant

La Quinta, CA 92253

760.564.0884 (Phone, Fax and Answering Machine)