Return to index: [Subject] [Thread] [Date] [Author]

Re: Question for the snow gurus

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Dan,

	No, I don't have any experience with this type of roofing system.

	My experience is limited to structural only.  I have designed a few
buildings with snow loads in the 100 to 200 p.s.f range but all of them
have either been (nearly) flat or much steeper than 5/12 to remove snow
before it builds up to this level.

	I do know of one fatality from snow sliding off a roof.  As I recall it
was in or near Revelstoke, B. C. several years ago.  A small child went
missing and was subsequently found under the snow from the roof.

	It's common for buildings (mostly pre engineered) at industrial
facilities to be equipped with "ice rakes" or gable canopies above
doorways to protect employees against falling ice or snow.  The snow
loads I have experienced with these is more like 40 p.s.f. or less.

	There is a publication by National Research Council of Canada, in their
Canadian Building Digest, Division of Building Research, on this topic. 
It is CBD 228, Sliding Snow on Roofs.  It won't tell you much more than
I have already; but it will some formal back-up if you need it.  Their
address is 

Division of Building Research,
National Research Council of Canada,
Ottawa, Canada. K1A 0R6
I do not know their e-mail address or their telephone number.

	I hope this helps.

				Regards,

				H. Daryl Richardson

Dan Goodrich wrote:
> 
> 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
> > >
> > >
> >
> > ******* ****** ******* ******** ******* ******* ******* ***
> > *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> > *
> > *   This email was sent to you via Structural Engineers
> > *   Association of Southern California (SEAOSC) server. To
> > *   subscribe (no fee) or UnSubscribe, please go to:
> > *
> > *   http://www.seaint.org/sealist1.asp
> > *
> > *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> > *   send to the list is public domain and may be re-posted
> > *   without your permission. Make sure you visit our web
> > *   site at: http://www.seaint.org
> > ******* ****** ****** ****** ******* ****** ****** ********
> >
> 
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********