SnowLoadCheck

Washington County, IL Roof Snow Load - 20 psf

Washington County, IL roof snow load, translated

Moderate
20 psf

A typical heated home in Washington County is designed to carry 20 pounds per square foot of snow on its roof, per ASCE 7-22. 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.

On a roof that means 44 in. of fresh snow, 16 in. once it packs down, or 4 in. of solid ice - three very different piles for the same load. 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.

Washington County at a glance

Where Washington County ranks

#70 of 102 Illinois counties by design load, top 38% of 2,758 nationally - that's Washington County's spot. That's 0.7 psf above Illinois's own county-average design load of 19.3 psf.

FIPS 17189, population 13,535, centered near 38.3531°N 89.4172°W. ASCE 7's underlying ground snow load here is 20 psf before the code's exposure and importance factors bring it to the 20 psf design figure above.

Washington County: average annual snowfall

Washington County sees about 11.7 in. of snow most winters, per the NASHVILLE 1 E, IL US station's 1991-2020 NOAA normal. See the density guide.

Read this before you use Washington County's figure

The figure above assumes the case ASCE 7-22 treats as typical: a heated, ordinary-occupancy home on a partially exposed site. Change any of those - exposure, heating, roof pitch, occupancy category - and the real design number moves.

A building permit needs the number at your exact address, not the county average - the free ASCE 7 Hazard Tool returns that from your coordinates in about a minute and produces a PDF a plan reviewer will accept. See the methodology guide.