SnowLoadCheck

McLean County, IL Roof Snow Load - 20 psf

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

Moderate
20 psf

McLean County's roofs are built to hold 20 psf of snow, the ASCE 7-22 figure a permit reviewer checks first. §7.3.4's low-slope minimum of 20 psf is what actually governs on a flat or low-pitch roof here - higher than the 14 psf the base ground-load formula gives.

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. A meaningful design load. Most homes built to modern code handle it, but additions, carports, and flat-roofed sections are worth a second look.

McLean County at a glance

McLean County by the numbers

Nationally that's #602 out of 2,758 rated counties, the top 22%; within Illinois alone, McLean County ranks #13 of 102. That's 0.7 psf above Illinois's own county-average design load of 19.3 psf.

McLean County, FIPS 17113, is home to 172,069 people near 40.4946°N 88.8445°W. Its 20 psf ground snow load figure is the map value; 20 psf is what a roof is actually designed for.

McLean County's snowfall, most winters

20.1 in. a year: that's McLean County's NOAA 1991-2020 snowfall normal, measured at NORMAL 4NE, IL US (6.7 mi away). See the density guide.

Before you rely on McLean County's number

Treat the McLean 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. See the methodology guide.