[RE-wrenches] wind load

[William Miller]

Rebecca:

I am not a structural engineer, nor would I second guess a structural 
engineer's findings.  The audacity here is that your inspector posture's 
him/herself as knowing more than a licensed engineer and is imposing unfair 
demands.  Your maximum responsibility ends with an engineer's project 
specific wet stamp.

My complaint is when I receive impromptu demands from a building 
inspector.  I insist that every requirement be published and equally 
enforced.  If the AHJ wants an engineering report on every roof mount 
installation, so be it -- as long as every contractor and owner-builder has 
the exact same requirement and the requirement is in writing in a publicly 
accessible forum.  Then at least the playing field is level and all 
contractor's know what to expect when bidding a job.

The down side to heightened requirements imposed by an AHJ is that it makes 
all installs more expensive, allowing fewer projects to be completed and 
leaving your area with a larger carbon foot print.

I have a clause in my contract that allows extra charges if a standard 
permit package proves inadequate.  This requires a change order signed by 
the client.  The client will be informed immediately if the project gets 
bogged down with unfair or arbitrary demands.  This way the client can get 
involved politically, if appropriate.  If it becomes necessary, the more 
angry calls your county elected officials receive, the better.

I hope this is helpful information.  I think you can tell I have had some 
bad experiences!

William Miller


At 04:03 AM 12/5/2009, you wrote:
>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 
>><<mailto:william at millersolar.com>william at millersolar.com>
>>To: RE-wrenches 
>><<mailto:re-wrenches at lists.re-wrenches.org>re-wrenches at lists.re-wrenches.org>
>>Subject: Re: [RE-wrenches] PV wind load
>>Message-ID: 
>><<mailto:6.0.1.1.2.20091204220550.061cd348 at millersolar.com>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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