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Re: Wind load design for Photovoltaic panel installations

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Agreed.  A solar panel weighing 3 psf, standing off 6" from the roof surface having a pitch of 8:12, essentially takes the place of the 16 psf roof live load.  Once the panel is removed for a reroof, then the roof structure should still be adequate for a 16 psf live load, with a 7-day load duration factor (per NDS for wood) of 1.25.
Yes, if the panel is inclined near vertical to a "flat" roof surface, then, yes, the roof still needs to support the panel weights in addition to the standard roof live load.
I may have lost track of Dennis' original post, but it seems to me (at least in the project I am looking at) that the roof members see no difference in their initial design.

On Wed, Aug 20, 2008 at 8:57 PM, Conrad Harrison <sch.tectonic(--nospam--at)> wrote:



I don't believe the live load becomes zero. My understanding is that the live loading allowance is for construction and maintenance. During Installation of the solar panels, that loading still needs to be allowed for on the house roof. However, if the solar panels are offset from the roof surface, then no additional live loading would be expected on the top of the solar panels themselves. There after no live loading can be applied to the roof below the panels, but that would be dependent on the angle of the panels relative to the roof slope. If the house roof is relatively flat and the panels are near vertical (relatively speaking), then can still access roof behind the panel.


But no one should be standing or stacking materials on the solar panel. From another perspective the panels could be considered a brittle roof structure. So if they are laid hard against the existing roof structure, and possible to walk from ordinary roof and accidentally tread on panels: then want the roof below to provide adequate support.


So I would say there is no additional live load applied to the panel, but also no live load removed from the roof.



Conrad Harrison

B.Tech (mfg & mech), MIIE, gradTIEAust



South Australia

David Topete, SE