Gary,
The snow loads that structural engineers design to are a worst-case scenario.
It is true that snow tends to slough off of PV arrays quicker than your normal
roof. However, if there is a major snow event, especially if it starts at night
(this recent blizzard on the East Coast would be a good example), snow will
build up on the array the same as it does everywhere else.
In many cases, a PV array actually makes the engineering assumptions worst. Any
snow that lands on the modules transfers down to the attachments, and
point-load the structural members. The weight of the snow is less distributed
when it sits on a PV array, placing additional stress on individual members. I
work in Massachusetts currently, and we often have to perform rafter upgrades
to roofs that are fine otherwise for exactly this reason.
If you have any snow load requirements in your area, I would highly recommend
you have a structural engineer review the structure, even if a structural stamp
is not required.
Jeffrey Quackenbush
________________________________
From: Bob-O Schultze <bo...@electronconnection.com>
To: RE-wrenches <re-wrenches@lists.re-wrenches.org>
Sent: Tuesday, February 19, 2013 3:00 PM
Subject: Re: [RE-wrenches] Snow loads
I would certainly agree with Will here. You can't make that argument as stated,
it's wrong. Please don't try to make it to your AHJ, you take the chance of
f-ing it up for everyone around there. I think the best argument you can try
is: aside from the usual 3-4lbs/sq/ft that the array itself ads to the roof
load, snow will be very unlikely to build up on the modules to the degree that
it builds up anywhere else on the roof. The freezing-rain-before-a-snow
phenomena is very real and it WILL happen sooner or later. Not often perhaps
and under most conditions the snow will leave the modules before the roof.
But...Gotta be real about that.
Bob-O Schultze
On Feb 19, 2013, at 11:06 AM, Will White wrote:
Most structural engineers I’ve seen take a reduction for slippery surface but I
think you’d be stretching things to say adding PV panels reduces the load to
zero. I have a 45 degree pitch roof and I get snow build up some times
especially if we get freezing rain before the snow.
Also if you have an asphalt shingle roof you can create an unbalanced load with
snow sliding off the south side and sticking on the north side. Most engineers
take this into consideration too.
Thanks,
Will
__________________________________________________________________________________________
Will White
Regional Field Operations Manager – New England
Real Goods Solar
64 Main St.
Montpelier, VT 05602
Tel: (802) 223-7804
Cell: (802) 234-3167
www.realgoodssolar.com
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Gary Bassett
Sent: Tuesday, February 19, 2013 1:48 PM
To: re-wrenches@lists.re-wrenches.org
Subject: [RE-wrenches] Snow loads
Has anyone in the snow belt areas have any luck with convincing their local
building inspectors that the snow melts or slides from panels, much like a
metal roof only better. Thus your snow load would be reduced to zero where the
panels have been installed.
Gary
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