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Unblaanced snow on 12 in 12 roof

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Title: Unblaanced snow on 12 in 12 roof


I didn't think there was that much difference between 7-02 and 7-05. We did a comparison of 7-05 to 7-98 and didn't even see the magnitude of differences that you note below. Here's a link to our paper:

Take a look at that and see if it helps. If not, give me a few more specifics about your particular situation (e.g. span, ground snow load, etc.) and I'll see if I can help.


John "Buddy" Showalter, P.E.
Director, Technical Media
AF&PA/American Wood Council
1111 19th Street, NW, Suite 800
Washington, DC 20036
P: 202-463-2769
F: 202-463-2791

The American Wood Council (AWC) is the wood products division of the American Forest & Paper Association (AF&PA). AWC develops internationally recognized standards for wood design and construction. Its efforts with building codes and standards, engineering and research, and technology transfer ensure proper application for engineered and traditional wood products.

The guidance provided herein is not a formal interpretation of any AF&PA standard.  Interpretations of AF&PA standards are only available through a formal process outlined in AF&PA's standards development procedures.


From: "Jordan Truesdell, PE" <seaint1(--nospam--at)>
To:  seaint(--nospam--at)
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

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.