Hi Rebecca......when necessary we often locate the truss company thru the builder or the homeowner and have had very good luck with their engineers giving the their stamp to their own trusses as being capable of having a solar array of the requested size installed on that set of trusses.....<br>
Typically we approach their engineer with a set of information on the proposed array including weight, attachment method, spacing and frequency of attachments and typically the engineer is happy to look it over....typically free of charge...<br>
When you show the inspector or the permit plan checkers your array to roof attachment plan with the truss company engineers approval they feel that they are being removed from the liability of a failure and are much happier to go with your requests......<br>
Good Luck...<br> <br>-- <br>Sunny Regards,<br>Kirpal Khalsa<br>NABCEP Certified Solar PV Installer<br>Renewable Energy Systems<br><a href="http://www.oregonsolarworks.com">www.oregonsolarworks.com</a><br>541-218-0201 m<br>
541-592-3958 o<br><br><div class="gmail_quote">On Sat, Dec 5, 2009 at 12:19 PM, Chris Worcester <span dir="ltr"><<a href="mailto:chris@solarwindworks.com">chris@solarwindworks.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div bgcolor="white" link="blue" vlink="purple" lang="EN-US">
<div>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">One thing we’ve had to do here is stagger the connections
to the rafters from row to row thus each rafter is secured to, not every other
one. This is easy enough to do, and just adds one extra standoff or Quick Mount
in your case on the staggered row. (we are in a high snow load area and
the idea of offsetting the connection points to the rafters on every other row
is so the snow load doesn’t stress the rafters too much, spreading out
the weight)</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">This is a win-win solution that your inspector should have no
problem with.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Otherwise the truss to top plate connection might need to be
addressed by your structural engineer for its uplift value. Hopefully the home
had Simpson truss holdowns, like A-35 clips, installed during the framing, and
if this is in the original engineering that should suffice.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div>
<p class="MsoNormal"><span style="font-size: 10pt; color: navy;">Sincerely,<br>
<br>
Chris Worcester</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; color: navy;">Solar Wind Works<br>
NABCEP Certified PV Installer<br>
Phone: 530-582-4503<br>
Fax: 530-582-4603<br>
<a href="http://www.solarwindworks.com/" target="_blank">www.solarwindworks.com</a><br>
<a href="mailto:chris@solarwindworks.com" target="_blank">chris@solarwindworks.com</a><br>
"Proven Energy Solutions"</span><span style="font-size: 11pt; color: rgb(31, 73, 125);"></span></p>
</div>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div>
<div style="border-style: solid none none; border-color: rgb(181, 196, 223) -moz-use-text-color -moz-use-text-color; border-width: 1pt medium medium; padding: 3pt 0in 0in;">
<p class="MsoNormal"><b><span style="font-size: 10pt; color: windowtext;">From:</span></b><span style="font-size: 10pt; color: windowtext;">
<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>
[mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of </b>Kent
Osterberg<br>
<b>Sent:</b> Saturday, December 05, 2009 8:46 AM<br>
<b>To:</b> RE-wrenches<div class="im"><br>
<b>Subject:</b> Re: [RE-wrenches] wind load</div></span></p>
</div>
</div>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Rebecca,<br>
<br>
With three rows and six lags in every other rafter there is a tremendous force
on each of the rafters. Unirac has excellent information in their
installation <a href="http://www.unirac.com/pdf/ii227.pdf" target="_blank">manual</a> that
shows all the engineering info needed for ASCE-7, which is meets the
requirements for most building departments. If you go through the
calculations, you can determine the maximum force or load on each lag
bolt. And you should go through the calculations to make sure that the
spacing and lag bolt penetration is adequate. The adequacy of the roof
structure is a question for the structural engineer. Modern truss
structures will handle it, and presumably that's what your structural engineer
looked into. At this point, I agree with William: it is time to go over
the inspector's head with the argument that he doesn't have the authority to
question the engineering.</p><div class="im"><br>
<br>
Kent Osterberg<br>
Blue Mountain Solar<br>
<br>
<br>
<br>
Rebecca Lundberg wrote: </div><div class="im">
<p class="MsoNormal">Hi William,<br>
<br>
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.<br>
<br>
Rebecca</p>
</div><div>
<blockquote style="border-style: none none none solid; border-color: -moz-use-text-color -moz-use-text-color -moz-use-text-color rgb(204, 204, 204); border-width: medium medium medium 1pt; padding: 0in 0in 0in 6pt; margin-left: 4.8pt; margin-right: 0in;">
<p class="MsoNormal"></p><div class="im"><br>
Message: 3<br>
Date: Fri, 04 Dec 2009 22:21:43 -0800<br>
From: William Miller <<a href="mailto:william@millersolar.com" target="_blank">william@millersolar.com</a>><br></div><div class="im">
To: RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>><br></div><div class="im">
Subject: Re: [RE-wrenches] PV wind load<br>
Message-ID: <<a href="mailto:6.0.1.1.2.20091204220550.061cd348@millersolar.com" target="_blank">6.0.1.1.2.20091204220550.061cd348@millersolar.com</a>><br></div><div><div></div><div class="h5">
Content-Type: text/plain; charset="us-ascii";
Format="flowed"<br>
<br>
Rebecca:<br>
<br>
It sounds like you have made an air-tight case (pun intended) and you have<br>
still not been able to convince this thick-headed inspector. I have had a<br>
similar experience last summer that might be relevant: After being pushed<br>
around beyond my patience, I fought back. I worked up the chain of<br>
command, stayed professional and put it all in writing.<br>
<br>
I won the battle and set a precedent. I have forbidden the building<br>
department from assigning the problem inspector to my projects and, to my<br>
amazement, the department obeys my request!<br>
<br>
Good luck, and let us know how it turns out<br>
<br>
William Miller<br>
<br>
<br>
<br>
At 05:55 PM 12/4/2009, you wrote:<br>
>Solar is somewhat 'new technology' where I live. :-) I have a building<br>
>inspector that feels that (32) Sanyo modules (6.88 kW array) mounted to a<br>
>house roof is going to cause undue stress to the roof truss (it is a<br>
>regular house in a Minnesota suburb, building height is 26', 30 degree<br>
>roof angle, in a suburban neighborhood. 2" x 4" manufactured
truss). We<br>
>are leaving 12-24" on each edge with no PV, and are careful to attach
to<br>
>the center of each rafter.<br>
><br>
>The inspector is not that concerned with dead load, but is especially<br>
>concerned with wind load. We have provided an engineering letter that<br>
>ascertains that a solar array mounted parallel to the roof surface is well<br>
>within the parameters of what a typical roof truss can handle. We were<br>
>required to have an engineer look at this address specifically, so we then<br>
>provided an additional engineer's letter that affirmed that yes, solar<br>
>mounted in the manner we proposed (with Quick-Mount attachment and Unirac<br>
>SolarMount rails, all installed according to manufacturers' instructions)<br>
>would be fine on this home. The building inspector insists that the wind<br>
>load is excessive, and wants more analysis. Do any of you have ideas,<br>
>experience, or data that might help me?<br>
><br>
>Rebecca Lundberg</div></div>
</blockquote>
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