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Re: Photovoltaic panel weights

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The sliding snow will hit the ground, there is no lower structure to consider. The entrance ramp is on one of the gable end sides.

On 3/17/2014 5:56 PM, Michael James wrote:
Drew,

Being outside the building envelope, the solar panels would probably
use the unheated slope factor chart regardless. At 4:12 the slope factor is almost negligible. However note that the slope factor reduces snow load, the chart overstates the slopes required for snow to slide in order to be
conservative (i.e. snow will almost always slide off a 12:12 pitch before
reaching what would otherwise be the full design load in the absence of
sliding, so it is OK to reduce). Referring to Sec 7.9 (ASCE 7-05), load
caused by sliding snow is a consideration beyond 1/4:12 slope if slippery
or 2:12 slope if not slippery. This is almost certainly conservative going the other way (i.e. snow will most likely never slide off roofs below this pitch) My own practical observations and experience would suggest that in reality snow will really begin to slide off a surface somewhere in between these two extremes. Solar panels in particular seem to warm up once the sun hits any exposed area of the panel, which appears to precipitate melting and sliding under the right conditions. Point I'm getting at is that while you may not be able to get the reduction there is still a good chance that snow could slide off the panels which requires at least a passing consideration of where such snow would end up.

Truncated 1342 characters in the previous message to save energy.

--
*
Drew Morris, PE*| Project Engineer
BBFM Engineers, Inc. <http://www.bbfm.com/>
510 L Street, Suite 200 | Anchorage, Alaska 99501
Ph: (907)274-2236 | Direct: (907)270-2240 | Web: www.bbfm.com

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