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RE: Unblaanced snow on 12 in 12 roof (UNCLASSIFIED)

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Classification:  UNCLASSIFIED 
Caveats: NONE

I always check unbalanced snow for rafters, roof deck, headers and ridge
beam. I've found in Alaska it almost always controls. I think I've seen a lot
of people wrongly assume the balanced snow will produce bigger affects.  

The new ASCE 7 formulas make it a pain in the but for over 20'=W where I used
to be able to do it quickly with a calculator. 

Whoever wrote the new unbalanced snow formulas should be waterboarded at
Gitmo.

-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com] 
Sent: Saturday, February 03, 2007 4:47 AM
To: seaint(--nospam--at)seaint.org
Subject: Unblaanced snow on 12 in 12 roof

I was just looking at an existing roof the the owner would like to add some
new load to.  The slope is 12 in 12, in an uninsulated attic space, 25psf
ground snow load. By my reading in ASCE 7-05, the entire roof effectively has
to be designed for Ixpg=25psf, whereas in the past
(ASCE7-02) the load would be 1.5ps = 1.5*(0.7*I...*pg)*Cs or
1.5*(0.7*1*...*25)*0.6 = 15.75 psf.

Is there some errata I've missed? This is nearly a 60% load increase from the
previous code. I realize that it only affects steeper roofs (8 in 12 to 32 in
12), but it seems like there's a gap in the code application. 


By the way - does anyone actually check to see if ridge board roofs work for
unbalanced snow loads, or do we all just close our eyes and hope that a
couple .131 toenails and friction keep the roof from collapsing? 
Experience dictates the latter - both on paper and in the field.

-- 

Jordan


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Classification:  UNCLASSIFIED 
Caveats: NONE


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