Snow loads for steel buildings, explained without the jargon

Ground snow load vs. roof snow load

Ground snow load (Pg) comes from a code map — 20 psf in Columbus, 25 in Cleveland, 30 in Pittsburgh. Your engineer converts it to a flat-roof load using exposure, thermal, and importance factors, which usually lands somewhere between 70% and 100% of Pg.

Drift is where the money goes

Snow does not sit evenly. It piles against parapets, against taller adjacent structures, and — most commonly on the buildings we quote — against the wall where a lean-to meets the main building. Drift loads routinely run two to three times the flat-roof load in that strip, and they govern the framing there.

Practical decisions this affects

• Roof pitch: steeper roofs shed more, which can reduce the design load slightly, but they add panel area and cost.
• Lean-to placement: putting a lean-to on the leeward side changes the drift case, sometimes dramatically.
• Unheated buildings: a cold building carries a higher thermal factor than a heated one, so an unheated shop is designed for more snow than a heated one.
• Openings near drift zones: a big door under a drift strip may need a heavier header than the same door elsewhere.

If you don't know your snow load

That is completely normal and it does not slow your quote down. Give us the project ZIP and we pull the ASCE 7 value and any local amendment during estimating. It gets flagged on your project record as needing verification until an engineer confirms it.