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Re: ASCE 7-05 Section (#4) clarification needed

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What Scott says goes along with our Canadian codes.

Dennis Wish wrote:

This makes more sense and I would have to yield to you on this because of the lack of snow loads in the majority of Southern California. According to the 97 UBC we applied what the building official provided as the snow load for the elevation and region regardless of slope and had an increase on the eaves. The wording of this section is somewhat ambiguous for those of us not familiar with snow loads according to the IBC provisions.

Unless anyone else has another interpretation, I will accept Scotts explanation of snow loading and add this to Multi-lat(mt). Thanks Scott.


*From:* Scott Maxwell [mailto:smaxwell(--nospam--at)]
*Sent:* Sunday, July 20, 2008 7:06 AM
*To:* seaint(--nospam--at)
*Subject:* RE: ASCE 7-05 Section (#4) clarification needed

I interpret this as if the flat roof snow load (Psubf) exceeds 30 psf, then you take 20% of the FLAT roof snow load (Psubf) and add that to the seismic mass. You do NOT take 20% of the SLOPED roof snow load (Psubs)...that is the "regardless of actual roof slope" part. And you do NOT take 20% of the portion that exceeds 30 psf.

Thus, if you have a 40 psf flat roof snow load and a 12:12 roof pitch on a non-slippery roof such that the sloped roof snow load is 24 psf, then you would add 8 psf (20% of 40 psf) to the seismic mass...NOT 4.8 psf (20% of 24 psf).



Adrian, MI

    -----Original Message-----
    *From:* Dennis Wish [mailto:dennis.wish(--nospam--at)]
    *Sent:* Saturday, July 19, 2008 9:56 PM
    *To:* seaint(--nospam--at)
    *Subject:* ASCE 7-05 Section (#4) clarification needed

    I need an interpretation to note number 4 of ASCE 7-05 Section which states:

    “Where the flat roof snow load, Pf, exceeds 30 psf (1.44 kN/m^2),
    20 percent of the uniform design snow load, regardless of actual
    roof slope.”

    This seems to conflict with itself. My first interpretation is
    that if the snow load for a flat roof (say ¼” in 1-foot) slope or
    a shed roof exceeds 30 psf then you would add 20% or 6 psf to the
    roof dead load. However, the last section of the statement reads
    “regardless of actual roof slope” in which case I would interpret
    the 20% of the Snow Load exceeding 30-psf to be added to any
    sloped roof.

    How do others interpret this statement. If the roof is flat should
    20% of any Snow Load be considered whereas only 20% of the Snow
    load exceeding 30-psf be used if the roof is pitched?

    Dennis S. Wish, PE

    Dennis S. Wish, PE

    California Professional Engineer

    Structural Engineering Consultant

    La Quinta, CA 92253


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