Paul,
That’s the first I’ve ever heard of the concept of increasing wind loads due to built-up snow. Although I will grant most of my experience is mid-Atlantic
I can’t see it making much of a difference. It doesn’t seem to me, even with heavy snow buildup, that you’d increase the mean roof height much more than 5 feet or so. That translates (glancing at the height adjustment tables) to about a 5% increase in the wind pressure. But the wind load is nowhere near that accurate to begin with. For starters, if you’re using the low-rise method, you’re locked to the design pressures for 30 feet mean roof height even if you only have a 15 or 20 foot mean roof height. Then if you’re in Exposure B, you’re actually designing to almost an Exposure C surface roughness; the roughness values picked for Exposure B are at the lower bound (i.e. nearly open terrain).
Plus, if you’ve got that much snow it’s probably building up on the ground as well as on the roof too. So “grade plane” is higher too…
Regards,
Gary J. Ehrlich, PE
Program Manager, Structural Codes & Standards
National Association of Home Builders (NAHB)
ph: 202-266-8545 or 800-368-5242 x8545
fax: 202-266-8369
gehrlich@nahb.com
From: Paul Blomberg [mailto:paul.blomberg@gmail.com]
Sent: Tuesday, June 10, 2008 2:44 PM
To: seaint
Subject: Wind Load on Deep Snow Profile
I'm putting together design criteria and am curious how you handle / take into consideration the added projected wind surface area due to built up snow on the roof of a building?
I have a new metal building going into northwestern
I normally include this additional snow profile to calc the wind loads but this my first heavy snow load situation where the increased load is significant.
Paul.
Phoenix, AZ