[RE-wrenches] Structural Review for Residential PV Systems

[Bruce Leininger]

A local jurisdiction is starting to require that we document non-truss 
rafter dimensions, span and attachment points.  This seems to be a fad 
that other jurisdictions have required at times, and other times not.  
When the existing structure was deemed insufficient, we've either paid a 
structural engineer to do some calcs and recommend more attachment 
points, or sistered the rafters to match the spacing given in the 20 psf 
table in the UBC.

Would the dead load from the PV modules ever be more than that from 
adding a second layer of comp roofing, which does not require a 
structural analysis?  Would the live point loads from the PV system ever 
be greater than the point load of a person walking on the roof?  If the 
answers are "no" and "no", then it seems that a roof that supports a 
person walking on it would not be adversely affected by the installation 
of a non-ballasted residential PV system.

I looking for help with the following:

    1.  Has there been an occasion when a residential PV system
    (non-ballasted), that was installed per the manufacturer's
    instructions, detached from a roof or caused damage to the structure
    of the roof?
    2.  Is there a good explanation for why structural review for
    residential PV systems is necessary?
    3.  Are there studies or resources that I can present to building
    officials to explain why structural review for residential PV
    systems is not necessary?

Thanks for your help.

Bruce

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