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Re: Question for the snow gurus

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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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