Snohomish County, WA Roof Snow Load - 15 psf
What ASCE 7 says about snow load in Snohomish County
That's Snohomish County's design roof snow load per ASCE 7-22, for a typical heated single-family home - the number a permit reviewer starts from. The physics-based figure alone would be 10.5 psf, but ASCE 7's own low-slope minimum (§7.3.4) sets a floor of 15 psf for flat and low-pitch roofs here, which is the number that actually governs.
Converted to something you can actually eyeball on a roof: about 33 in. of fresh powder, 12 in. once it settles and packs down, or just 3 in. if it's turned to ice. This is a meaningful design load - most modern-code homes handle it fine, though an addition, a carport or a flat-roofed section can be a weak spot.
Snohomish County in numbers
- Design roof snow load15 psf
- Ground snow load, ASCE 7 map15 psf
- National rank#1,308 of 2,758
- Washington rank#5 of 10
- Population864,113
- Annual snowfall, NOAA normal3 in.
- FIPS53061
Where Snohomish County's figure sits nationally
Out of 2,758 rated US counties, Snohomish County sits at #1,308, the top 47% nationally - #5 of 10 within Washington. 16 psf is Washington's typical county figure - Snohomish County comes in 1 psf under it.
Near 48.0549°N 121.765°W, FIPS 53061: Snohomish County counts 864,113 residents and a 15 psf map value, which the code's own factors turn into 15 psf.
How much it actually snows in Snohomish County
Most winters bring Snohomish County roughly 3 in. of snow - NOAA's normal at MONROE, WA US, 18 mi off. (fresh vs. packed vs. ice explains why.)
Read this before you rely on it
Snohomish County's number above is ASCE 7-22's default case, not a custom calculation: ordinary residential occupancy, heated, sited on ground that's neither fully sheltered nor fully exposed. Any one of those changing - pitch, exposure, heating, occupancy - moves the real figure.
Nothing here substitutes for an address-level number. Get one free, in about a minute, from the ASCE 7 Hazard Tool using your own coordinates rather than Snohomish County's county-wide figure. Details: the calculation guide.