SnowLoadCheck

Mason County, IL Roof Snow Load - 20 psf

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

Moderate
20 psf

Mason 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 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.

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. This is a meaningful design load - most modern-code homes handle it fine, though an addition, a carport or a flat-roofed section can be a weak spot.

Mason County in numbers

Mason County by the numbers

Nationally that's #1,064 out of 2,758 rated counties, the top 39%; within Illinois alone, Mason County ranks #74 of 102. That's 0.7 psf above Illinois's own county-average design load of 19.3 psf.

Mason County, FIPS 17125, is home to 12,543 people near 40.237°N 89.9136°W. Its 20 psf ground snow load figure is the map value; 20 psf is what a roof is actually designed for.

Mason County's snowfall, most winters

12.9 in. a year: that's Mason County's NOAA 1991-2020 snowfall normal, measured at MASON CITY 4SE, IL US (14.7 mi away). See the density guide.

Before you rely on Mason County's number

Treat the Mason 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. Details: the calculation guide.