SnowLoadCheck

Jefferson County, IL Roof Snow Load - 20 psf

Jefferson County, IL: your roof's ASCE 7 snow number, in plain English

Moderate
20 psf

Jefferson County's roofs are built to hold 20 psf of snow, the ASCE 7-22 figure a permit reviewer checks first. ASCE 7's low-slope-roof minimum (§7.3.4) raises the governing figure to 20 psf - higher than the 14 psf the ground-load formula alone would give, and the code says use the larger one.

In depth, not weight: that's roughly 44 inches of fresh, light snow, 16 inches of old, settled snow, or as little as 4 inches of solid ice - snow that heavy is rare here but ice from a freeze-thaw cycle adds up far faster than the depth suggests. 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.

Jefferson County at a glance

Jefferson County by the numbers

Nationally that's #807 out of 2,758 rated counties, the top 29%; within Illinois alone, Jefferson County ranks #35 of 102. That's 0.7 psf above Illinois's own county-average design load of 19.3 psf.

Jefferson County, FIPS 17081, is home to 36,107 people near 38.3008°N 88.9242°W. Its 20 psf ground snow load figure is the map value; 20 psf is what a roof is actually designed for.

Jefferson County's snowfall, most winters

10.4 in. a year: that's Jefferson County's NOAA 1991-2020 snowfall normal, measured at MT VERNON 3 NE, IL US (5.1 mi away). See the density guide.

Before you rely on Jefferson County's number

Treat the Jefferson County figure as a starting point, not a final answer: it assumes standard occupancy, a heated structure and a moderately sheltered site, per ASCE 7-22's own defaults. Exposed terrain, an unheated building or a steeper roof all shift the real number.

For a real application, skip the county number and go straight to the ASCE 7 Hazard Tool - enter your coordinates and it returns a site-specific figure a plan reviewer will recognize. (How this figure is calculated.)