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RE: Snow Loads

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I don't think the assumption that "snow will still slide off" an un-obstructed roof is quite correct. In snow country you can always see that snow is accumulated in the valleys of such roofs and there are many studies to show that. You could use UBC as a guideline. Canadian and European codes have also some recommendations.
Reza Dashti P.Eng
Vancouver, BC


Subject: RE: Snow Loads
Date: Fri, 9 May 2008 13:25:06 -0400
From: gehrlich(--nospam--at)
To: seaint(--nospam--at)



I presume you’re talking about the typical valleys in a gable/dormer roof system? (As opposed to industrial sawtooth roofs, folded-plate roofs, etc.)


There is not, to my recollection, a specific provision for typical valleys in ASCE 7-05. The question has come up a couple of times in the Snow Loads subcommittee as we work on the ASCE 7-10 updates. The general feeling seems to be that there is not an issue as long as the valley is unobstructed by a parapet or other feature; the assumption is the snow will still slide off. If you feel the snow won’t slide, you could take Cs = 1.0 and also Ce = 1.2 for a “sheltered roof” (per footnote ‘a’ of Table 7-2). Or you could use the sawtooth roof provisions, which I have done in the past, and you’ll be conservative. (At least according to the committee…)




Gary J. Ehrlich, PE
Program Manager, Structural Codes & Standards
National Association of Home Builders (NAHB)
1201 15th Street, NW, Washington, DC 20005
ph: 202-266-8545  or 800-368-5242 x8545
fax: 202-266-8369

From: Martin N. Pohll [mailto:mpohll(--nospam--at)]
Sent: Friday, May 02, 2008 4:03 PM
To: seaint(--nospam--at)
Subject: Snow Loads


1997 UBC Appendix Section 1641.3.2 had provisions for snow loads at valleys.


Is there a similar provision in ASCE 7-05


Martin N. Pohll

6934 Domingo Court

Rancho Murieta, CA 95683

(916) 769-4620

(916) 354-0581

(916) 354-3820 FAX


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