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RE: Snow Drift load in Roof Valleys

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I stand corrected - I thought I saw something about drift loads in valleys
in ASCE 7.  I don't doubt that that additional load is substantial, but I
don't see anywhere where ASCE (or IBC for that matter) requires you to
design for it.  Maybe they will add that in the next ASCE 7?


-----Original Message-----
From: Joe Grill [mailto:jgrill(--nospam--at)swiaz.com]
Sent: Wednesday, October 20, 2004 12:13 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Snow Drift load in Roof Valleys


Actually, I don't agree.  The valley surcharge that Mike is referring to in
the "97 UBC is very evident in high snow load country.  You really see it in
the spring when the areas away from the valley have melted and the
surcharged snow areas in the valleys remain.  Somewhere at home I have a
copy of one of the services documents (maybe the Corps of Engineers) that
have a lot of great photos that show why the snow provisions are the way
they are (or were anyway).
Joe Grill

-----Original Message-----
From: Brian S Bossley [mailto:bsbossley(--nospam--at)venturaengineering.com]
Sent: Wednesday, October 20, 2004 8:49 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Snow Drift load in Roof Valleys

IBC references ASCE 7 in the first paragraph, which has all the information
you would need for snow drifts.


-----Original Message-----
From: Michael L. Hemstad [mailto:hemstad.ml(--nospam--at)tkda.com]
Sent: Wednesday, October 20, 2004 11:40 AM
To: seaint(--nospam--at)seaint.org
Subject: Snow Drift load in Roof Valleys


List,
For gable roofs with intersecting ridge lines (i.e. for L-shaped
buildings), 1997 UBC Appendix Chapter 16, in Section 1641.3.2, dictated
an increased accumulation of snow in the valleys caused by the roof
intersections.  Figure A-16-12 shows a good picture of what I mean.  I
can't find anything like that in the IBC (I'm looking at 2000), only a
general unbalanced load for any gable roof, ignoring the valley effect
of such intersections.

Does anyone have any background as to why the valley drift criteria were
not included in the IBC, or have I just not found it?

Thanks,

Mike Hemstad, P.E.
TKDA
St. Paul, Minnesota

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