Peer-to-Peer Standards Exchange

 Snow drift on adjacent building with gable roof

  • ASCE Standards
  • Snow and Rain Loads
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Anonymous Member posted 03-19-2024 01:51 PM
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I am working on a project with a new building being constructed adjacent to a an existing building with a gable roof. Per ASCE 7, i know unbalanced snow loading is not required for a gable roof with a slope exceeding 7 to 12. Would a gable with a slope exceeding 7 to 12 need to still be designed for the full or a reduced snow drift from the adjacent building? 

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Christian Parker

Interesting question.  I'm picturing the new building roof below the eave height of the existing--is that correct?

At first blush, I don't think the relief ASCE 7 provides for unbalanced load applies to drift on an adjacent building.  Unbalanced load would be mainly along the ridge, internal to the existing building footprint, and it's easy to picture why high-slope pitched roofs wouldn't be subject to a concentration of snow at the ridge, with wind stagnating on the windward side and snow-laden air being directed up and away at the ridge (the commentary just says that significant unbalanced load on high-slope roof has not been observed).  For drift, I suppose sheltering of the leeward face in a high-slope gable roof might somewhat reduce the load all the way on the other side of the lot, but I wouldn't count on this being a significant reduction.  You should check sliding snow however, this may govern anyway.

While I haven't got too deep into 7-22, I've heard that the method is substantially different and includes a winter wind speed factor, which you could potentially play around with to get an order of magnitude sense for whether any reduction is realistic.