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Snow Drift from BOCA 1978 or 1981

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Title: Snow Drift from BOCA 1978 or 1981

Greetings all.

Does anyone out there have access to BOCA 78 or 81?  I'm interested in the Snow Drift requirements on lower level roofs for multi-level roof building.

I have a copy of BOCA 84 the formula is as follows:

                                Cs=15*h/g

                                Cs min = 0.8
                                Cs max = 3.0
                                h = Difference of roof heights
                                g = ground snow load (from 25,50,100 yr maps)
                               
                                Drift = Cs*g   
                               
I'm having a "discussion" with an Architect who insists on putting 2 story buildings right next to single story buildings.

In this particular case I'm looking at a set of drawings from 1983 were this was done and the lower roof (good for about 50psf) was "not" reinforced.  According to BOCA 99 the max drift load would be about 90 psf on the lower roof.  So the Architect wants to put another 2 story on the other side of the building, and wonders "What's all the fuss!"

So before I approach the owner with the information that his existing roof is not adequate by today's standards, I want to see if the original design was flawed.

Thank for your input.

Keith Hyndman, P.E.
khyndman(--nospam--at)engineeringsi.com
Engineering Solutions Inc.
436 Creamery Way, Suite 100
Exton, PA 19341
Phone: 610-524-1357
Fax: 610-524-1317