Unbalanced Snow Loads on Sawtooth Roof

[BouncedPod]

All,

I am currently working on an addition to an existing pre-engineered metal building and need some opinions as to the correct unbalanced snow load to apply to a sawtooth type roof. I am designing according to ASCE 7-10 section 7.6.3. The existing and proposed buildings have different roof slopes which leads to different ridge heights, and would like some clarification to ASCE's statement "However, the snow surface above the valley shall not be at an elevation higher than the snow above the ridge". Which ridge does everyone interpret ASCE to refer to, or do the unbalanced snow loads even apply because the addition roof slope is less than the noted 3/8:12? Refer to the attachment for clarity.

 

[RPMG]

Slopes 3/8" and less are flat roofs, not sawtooth.

For sawtooth roofs, one just draws a flat line of snow, with the depth varying with the roof elevation. There are minimums/maximums in the code.

 

[BouncedPod]

RPMG,

Is it your view then that if only one of the roof slopes is less than 3/8:12, noted in ASCE 7 section 7.6.3 as the limit to apply unbalanced snow loads to sawtooth roofs, that the section does not apply?

 

[RPMG]

I don't download attachments from this site because it isn't secure, so I'm not sure that I understand the question. The sawtooth provisions apply to slopes greater than 3/8". One section of less slope would not unclassify the whole roof as non-sawtooth.


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[BouncedPod]

The existing roof has a slope of 1.5:12 and the proposed roof is planned to match eave heights a slope up and away from the eave at a slope of 1/4:12 creating a valley. I am looking for clarification as to whether one slope of greater than 3/8:12 and one slope less than would classify the roof as a sawtooth and therefore force unbalanced sawtooth snow loads to be added to the existing building.

 

[RPMG]

New additions do not add balanced/unbalanced snow load to existing buildings. Snow drift is a separate topic that has its own provisions.