De Witt County, IL Roof Snow Load - 20 psf
De Witt County, IL: your roof's ASCE 7 snow number, in plain English
De Witt County's roofs are built to hold 20 psf of snow, the ASCE 7-22 figure a permit reviewer checks first. 14 psf is what the ground-load formula alone gives; De Witt County's 20 psf low-slope minimum (§7.3.4) beats it, so that figure is the one that governs on flat and low-pitch roofs.
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.
De Witt County at a glance
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map20 psf
- National rank#1,020 of 2,758
- Illinois rank#64 of 102
- Population15,319
- Annual snowfall, NOAA normal20.7 in.
- FIPS17039
De Witt County by the numbers
Nationally that's #1,020 out of 2,758 rated counties, the top 37%; within Illinois alone, De Witt County ranks #64 of 102. Illinois counties average 19.3 psf; De Witt County runs 0.7 psf higher than that.
De Witt County, FIPS 17039, is home to 15,319 people near 40.1815°N 88.9019°W. Its 20 psf ground snow load figure is the map value; 20 psf is what a roof is actually designed for.
De Witt County's snowfall, most winters
20.7 in. a year: that's De Witt County's NOAA 1991-2020 snowfall normal, measured at CISCO, IL US (15.1 mi away). See the density guide.
Before you rely on De Witt County's number
Treat the De Witt 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.)