Rip, Going down the road of engineering on every roof is a very slippery slope (particularly with ice and snow). The idea that a roof designed for 30psf would get in trouble with an additional 3psf is ridiculous. The Inspector Guidelines that I wrote, which are based many jurisdictions across the U.S. encourage the use of standard, engineered, stand-off mounting systems (e.g. UniRac, ProSolar, DPW, etc...) with buildings that have previously been inspected. If the building has never been inspected, then the rafter sizes and spacings should be provided, or truss calcs for trusses.
I understand that snow loads can be considerable (the Sierra's have locations requiring 300psf), but we also have hurricane locations and other loading issues. The biggest concern that I see with heavy snow loads is the point loading of the truss or rafter. In high snow load areas, the array should be located near the ridge (3') so that snow cannot accumulate above it, should be parallel to the roof, so that snow will not collect behind it, and have the mounting feet every 4-feet with alternating rafters used for the upper and lower rail connections. Rails should be run East-West on a South facing roof so that attachments can be adequately staggered. Snow has a greater tendency to shed from a glass surface making it more likely to be removed earlier than the rest of the roof. Encourage your local jurisdiction to use the Inspector Guidelines at www.irecusa.org. Bill. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Solar Plexus Sent: Tuesday, October 28, 2008 1:25 PM To: RE-wrenches@lists.re-wrenches.org Subject: [RE-wrenches] truss loading Hi All, We were recently notified by our local building department that all future building permits will require a letter from a state licensed engineer stating the existing roof trusses are adequate for the additional load a solar system will add. All roofs in our area have a 30 pound per square foot snow load requirement. The building departments concern is truss manufactures design the trusses to very tight tolerances and there is no room for additional load. Has anyone had to address similar requirements? Any ideas on how to approach this issue would be appreciated. Thanks in advance, Rip _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
