Roof Mount Arrays in Snow Country [RE-wrenches]

Bill Hoffer Sunergy at charter.net
Sun Jan 20 10:26:12 PST 2008


Johnathan

Years ago I designed a system for the North Cascades National Park here in
Washington.  A near flat roof with a very low pitch and 200 psf snow load.
We used Solarex modules and got them to sign a sheet saying that the modules
could handle the installation.  The season before the creeping snow load
completely ripped off the chimney!  To make the matter worse it was a metal
roof over a huge timber frame construction and they wanted to minimize
penetrations.  The mounting rails (4x6" tubular steel doublebacked taped to
roof to prevent ice ripping them off)were huge and we had to use Grade 8.2
fasteners.  Good thing that we got Solarex to sign the statement, but we did
not fail from snow load, but from ice forming under the modules (which were
8 inches off the roof). The ice popped up every piece of glass from the back
side up and destroyed every module.  Solarex replaced them and now they are
removed every winter! (facility is closed in winter as is the pass).  My
point is there is a very good reason that roofs are normally very steep
pitched in snow country, so snow sluffs off before it gets too built up
(code allows reductions in snow loads for steeper pitched roofs).  Be very
cautious about roof mount systems on a roof that is not properly designed
for the region or else you will end up footing a huge bill to replace those
modules!  Make sure your client signs an understanding of the possibilities
of severe damage to the arrays due to snow ice buildups.  I am sure that no
module manufacturer today would make the same mistake that Solarex did back
then!

Bill Hoffer
Sunergy Engineering Services
2504 Columbia Ave nw
East Wenatchee WA 98802
(509)884-8638
Sunergy at charter.net

PS my rails have survived perfectly!


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