St. Charles County, MO Roof Snow Load - 20 psf
How much snow is too much for a roof in St. Charles County, MO?
20 psf: that's what ASCE 7-22 requires a typical heated home's roof in St. Charles County to carry. Flat and low-pitch roofs in St. Charles 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. A meaningful design load. Most homes built to modern code handle it, but additions, carports, and flat-roofed sections are worth a second look.
St. Charles County in numbers
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map20 psf
- National rank#548 of 2,758
- Missouri rank#3 of 115
- Population423,726
- Annual snowfall, NOAA normal14.8 in.
- FIPS29183
How St. Charles County compares
20 psf ranks #548 of 2,758 US counties with a mapped snow load (top 20%) - and #3 of 115 in Missouri. That's 1.4 psf above Missouri's own county-average design load of 18.6 psf.
Population 423,726 (FIPS 29183), roughly 38.7811°N 90.6749°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 St. Charles County, MO
NOAA's 30-year normal for St. Charles County: 14.8 in. of snow a year, from the ST PETERS 2 SE, MO US station. (fresh vs. packed vs. ice explains why.)
What this St. Charles 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.
St. Charles 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. See the methodology guide.