SnowLoadCheck

St. Clair County, IL Roof Snow Load - 20 psf

How much snow is too much for a roof in St. Clair County, IL?

Moderate
20 psf

20 psf: that's what ASCE 7-22 requires a typical heated home's roof in St. Clair County to carry. The physics-based figure alone would be 14 psf, but ASCE 7's own low-slope minimum (§7.3.4) sets a floor of 20 psf for flat and low-pitch roofs here, which is the number that actually governs.

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. Clair County, IL: quick facts

How St. Clair County compares

20 psf ranks #573 of 2,758 US counties with a mapped snow load (top 21%) - and #9 of 102 in Illinois. 19.3 psf is Illinois's typical county figure - St. Clair County beats it by 0.7 psf.

Population 251,149 (FIPS 17163), roughly 38.4702°N 89.9285°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. Clair County, IL

NOAA's 30-year normal for St. Clair County: 11.2 in. of snow a year, from the BELLEVILLE SIU RSCH, IL US station. (fresh vs. packed vs. ice explains why.)

What this St. Clair 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. Clair 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. Details: the calculation guide.