[RE-wrenches] wind load

[Rebecca Lundberg]

Hi William,

Thanks for responding. We have three long rows of modules, with rails
attached every other rafter, every 4'. The inspector's argument is that two
attachments for one row might be fine, but that the wind load for the entire
array theoretically could be born by one rafter, and therefore it would pull
the rafter right out of the house. This is only my year 3 as an installer,
and while I'm not afraid to push the inspector if needed, I admit I want to
be sure he isn't right, even though an engineer says so (because I'm not an
engineer :-). So in your experience, is there a limit to an array size that
would be 'safe' for a home if the array is within the edges of the roof and
flush-mounted? I feel like that's the real argument, you might safely attach
one module, but he is saying when you multiply the modules you multiply the
wind load to the house by the same factor.

Rebecca

>
> Message: 3
> Date: Fri, 04 Dec 2009 22:21:43 -0800
> From: William Miller <william at millersolar.com>
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
> Subject: Re: [RE-wrenches] PV wind load
> Message-ID: <6.0.1.1.2.20091204220550.061cd348 at millersolar.com>
> Content-Type: text/plain; charset="us-ascii"; Format="flowed"
>
> Rebecca:
>
> It sounds like you have made an air-tight case (pun intended) and you have
> still not been able to convince this thick-headed inspector.  I have had a
> similar experience last summer that might be relevant:  After being pushed
> around beyond my patience, I fought back.  I worked up the chain of
> command, stayed professional and put it all in writing.
>
> I won the battle and set a precedent.  I have forbidden the building
> department from assigning the problem inspector to my projects and, to my
> amazement,  the department obeys my request!
>
> Good luck, and let us know how it turns out
>
> William Miller
>
>
>
> At 05:55 PM 12/4/2009, you wrote:
> >Solar is somewhat 'new technology' where I live. :-) I have a building
> >inspector that feels that (32) Sanyo modules (6.88 kW array) mounted to a
> >house roof is going to cause undue stress to the roof truss (it is a
> >regular house in a Minnesota suburb, building height is 26', 30 degree
> >roof angle, in a suburban neighborhood. 2" x 4" manufactured truss). We
> >are leaving 12-24" on each edge with no PV, and are careful to attach to
> >the center of each rafter.
> >
> >The inspector is not that concerned with dead load, but is especially
> >concerned with wind load. We have provided an engineering letter that
> >ascertains that a solar array mounted parallel to the roof surface is well
> >within the parameters of what a typical roof truss can handle. We were
> >required to have an engineer look at this address specifically, so we then
> >provided an additional engineer's letter that affirmed that yes, solar
> >mounted in the manner we proposed (with Quick-Mount attachment and Unirac
> >SolarMount rails, all installed according to manufacturers' instructions)
> >would be fine on this home. The building inspector insists that the wind
> >load is excessive, and wants more analysis. Do any of you have ideas,
> >experience, or data that might help me?
> >
> >Rebecca Lundberg
>
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