Washington County, MO Roof Snow Load - 20 psf
How much snow is too much for a roof in Washington County, MO?
20 psf: that's what ASCE 7-22 requires a typical heated home's roof in Washington County to carry. Flat and low-pitch roofs in Washington County are actually governed by ASCE 7's §7.3.4 minimum of 20 psf, not the 14 psf the ground-load formula alone would produce.
Picture it, not just weigh it: 44 in. if it's fresh powder, 16 in. once it settles, or a mere 4 in. if it's ice. Modern-code homes carry a load like this without issue; an older addition, a carport, or any flat-roofed section is where it is worth checking first.
Washington County at a glance
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map20 psf
- National rank#918 of 2,758
- Missouri rank#32 of 115
- Population23,583
- Annual snowfall, NOAA normal9.1 in.
- FIPS29221
How Washington County compares
20 psf ranks #918 of 2,758 US counties with a mapped snow load (top 33%) - and #32 of 115 in Missouri. Missouri counties average 18.6 psf; Washington County runs 1.4 psf higher than that.
Population 23,583 (FIPS 29221), roughly 37.9426°N 90.897°W. The 20 psf ground snow load ASCE 7-22 maps here becomes 20 psf once the code's own design factors are applied.
Typical snowfall in Washington County, MO
NOAA's 30-year normal for Washington County: 9.1 in. of snow a year, from the DE SOTO, MO US station. 25.3 mi is a real gap between Washington County and its nearest reporting station, so local snowfall can diverge from this figure, especially near elevation changes. (fresh vs. packed vs. ice explains why.)
What this Washington County figure assumes
This is a county-level reference figure for a typical heated home built to Risk Category II (ordinary residential), on a partially exposed lot - the assumptions ASCE 7-22 itself treats as the default case. A steeper roof, a fully exposed hilltop lot, an unheated structure, or a higher risk category all change the actual number.
Washington County's permit office wants an address-specific figure, not this county average - the ASCE 7 Hazard Tool is free, takes under a minute, and outputs a PDF most reviewers accept. (How this figure is calculated.)