Cook County, IL Roof Snow Load - 20 psf
Cook County, IL: your roof's ASCE 7 snow number, in plain English
Cook County's roofs are built to hold 20 psf of snow, the ASCE 7-22 figure a permit reviewer checks first. The physics-based figure alone would be 17.5 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.
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.
Already snow on the roof in Cook County?
Cook County at a glance
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map25 psf
- National rank#496 of 2,758
- Illinois rank#1 of 102
- Population5,182,617
- Annual snowfall, NOAA normal38.8 in.
- FIPS17031
Cook County by the numbers
Nationally that's #496 out of 2,758 rated counties, the top 18%; within Illinois alone, Cook County ranks #1 of 102. 19.3 psf is Illinois's typical county figure - Cook County beats it by 0.7 psf.
Cook County, FIPS 17031, is home to 5,182,617 people near 41.8943°N 87.6455°W. Its 25 psf ground snow load figure is the map value; 20 psf is what a roof is actually designed for.
Cook County's snowfall, most winters
38.8 in. a year: that's Cook County's NOAA 1991-2020 snowfall normal, measured at CHICAGO MIDWAY AP 3SW, IL US (12.8 mi away). See the density guide.
Before you rely on Cook County's number
Treat the Cook 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.)