Peer-to-Peer Standards Exchange

  • 1.  ASCE 7-22 Snow Load Updates

    Posted 06-26-2025 03:10 PM

    ASCE 7-22 updated the ground snow load map to reflect ultimate design loads, which increased the values. At the same time, the service-level load combinations now apply a 0.7 multiplier to snow loads.

    My concern is with how snow drifts are calculated. Drift loads are based on the drift height and the snow density. However, the equation for snow density wasn't updated to reflect the switch to ultimate loads.

    As a result, while the ground snow load increased, that increase doesn't really affect drift loads. But in design, we still apply the 0.7 multiplier to those drift loads. This means that when we start using ASCE 7-22, the drift loads we design for will end up being significantly lower than what previous codes required. Am I missing something?


    #ASCE7-22
    #LoadCombinations
    #SnowandRainLoads
    #SnowandRain

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    Jacob Trapp
    Fond Du Lac WI
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  • 2.  RE: ASCE 7-22 Snow Load Updates

    Posted 06-30-2025 07:25 PM

    The relationship between snow density and ground snow load does not change between the older 5-year MRI and newer reliability targeted loads.  Therefore adjustment of the load factor for ASD is not required.



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    Ronald Hamburger, SE
    Consulting Principal
    Simpson Gumpertz & Heger
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  • 3.  RE: ASCE 7-22 Snow Load Updates

    Posted 06-30-2025 08:35 PM

    To make it simple, let's use the following assumptions:

    • Ground snow ASCE 7-16 = 35 psf.
    • Ground snow ASCE 7-22 = 50 psf.

    Check service level roof pressure for an identical 4ft high snow drift.  

    • Density = 0.13pg +14 
      • 18.55 pcf (ASCE 7-16)
      • 20.5 pcf (ASCE 7-22)
    • Drift pressure = load factor x height x density. 

    ASCE 7-16

    • Service level drift pressure = 1.0 x 4 x 18.55 = 74.2 psf

    ASCE 7-22

    • Service level drift pressure = 0.7 x 4 x 20.5 = 57.4 psf

    Since the majority of the density equation is determined by a constant, an identical height drift is significantly lighter using ASCE 7-22. It is possible that previous codes were approximately 30% heavy on the assumed snow density. But, I have not heard that argument. 



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    Jacob Trapp
    Fond Du Lac WI
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    Original Message


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