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RE: Question for the snow gurus

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A little advice to the rocket scientist architect designing the roof that
lets snow slide onto pedestrians: change the direction the roof sheds. If
the snow just needs to be stopped above a door then put a cricket to
redirect the snow from the door [see UBC 1648 for ice splitters-crickets].
It is poor planning to have 3 feet deep snow fall 12 feet onto lawyers that
are out for a peaceful day skiing. Appendix UBC 1643 does not allow sliding
snow onto exits.

I have seen buildings up here that have slippery roof coverings with
intermediate "brakes?" along the slope of the roof. 

We have local amendments requiring ice and water shields at eaves. They work
great here Check out the UBC Chapter 15 local amendment roof covering tables
at the URL below.  

As for how snow behaves, I have a metal roof and it really launches a wad of
snow when it warms up after a good blizzard.

Scott M Haan P.E.
Plan Review Engineer
Building Safety Division http://www.muni.org/building
Development Services Department
Municipality of Anchorage
phone:907-343-8183  fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us



-----Original Message-----
From: Dan Goodrich [mailto:dang(--nospam--at)karren.com]
Sent: Thursday, June 28, 2001 5:15 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Question for the snow gurus


This is pretty close to what is obtained using the UBC formula.  Now
you have me curious.  I'm wondering if the other systems I've seen 
are being designed, or just put on randomly by the contractor.  They
don't look stout enough to contain the kind of forces I'm obtaining.

The architect has specified ice and water shield from the eave up to 3 ft.
from the ridge under the shingles.  Any experience with this causing a 
problem?

Thanks,
Dan Goodrich, P.E.
Utah

> Dan,
> 
> You should design for the weight of snow to be contained times the sine
> of the roof slope (5/13 in this case) because, under critical thaw
> conditions, all of the snow will try to slide off at once.
> 
> A word of caution: don't do this unless you are using a membrane
> roofing.  If you have shingles you can expect the contained snow to
> cause an ice dam which in turn will cause water to back-up under the
> shingles and leak large volumes of water into the building.
> 
> Regards,
> 
> H. Daryl Richardson,
> Calgary
> 
> > Dan Goodrich wrote:
> > 
> > I've designed a ski lodge where the snow load is 150 psf on a
> > 5/12 pitch roof.  The owner has asked about putting log railings
> > on the roof to help keep the snow on the roof, and not on the ground
> > in front of the windows and doors.  I am trying to determine what
> > force
> > to design the connection to the roof system.  UBC Appendix 1648
> > gives a force to design for vertical obstructions.  However, this
> > seems
> > very excessive, especially when compared to what I've observed on
> > other roof systems.  Anyone know of any other guidelines to follow,
> > or procedure?
> > 
> > Thanks,
> > Dan Goodrich, P.E.
> > Utah
> > 
> >
> 
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