Ground Snow Load Explained (and How to Find Yours)
What ground snow load (Pg) means, why it varies so much by location and elevation, and exactly where to look up the value for your site.
Ground snow load, written Pg, is the weight of accumulated snow on open ground at a site, in pounds per square foot. It is the single biggest input to any roof snow calculation, and it varies enormously: from 0 psf across the Gulf Coast to well over 100 psf in the mountains.
Why it varies so much
Snow load depends on climate and, crucially, elevation. Two towns in the same county can have very different ground snow loads if one sits a few thousand feet higher. That is why ASCE 7 marks mountainous regions as 'case study' zones, where a site-specific study is required rather than a single map value.
Where to find your value
The authoritative source is the ASCE 7 Hazard Tool, which returns the ASCE 7-22 ground snow load for a specific latitude/longitude. Your local building department is equally valid and often easier. Many adopt a published county or town value in their code amendments, and that adopted number is what governs a permit.
Ground vs roof snow load
Ground snow load is not what your roof carries. A normal heated, sheltered house carries roughly 60–70% of the ground value once the ASCE 7 factors are applied. Use the ground value as the starting point and convert it with the roof snow load calculator.
Get your design roof snow load in seconds with the free ASCE 7-22 calculator.
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