Winnebago County, IL Roof Snow Load - 20 psf
Winnebago County, IL roof snow load, translated
A typical heated home in Winnebago County is designed to carry 20 pounds per square foot of snow on its roof, per ASCE 7-22. §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 17.5 psf the base ground-load formula gives.
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.
Winnebago County at a glance
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map25 psf
- National rank#564 of 2,758
- Illinois rank#7 of 102
- Population283,790
- Annual snowfall, NOAA normal38 in.
- FIPS17201
Where Winnebago County ranks
#7 of 102 Illinois counties by design load, top 20% of 2,758 nationally - that's Winnebago County's spot. Illinois counties average 19.3 psf; Winnebago County runs 0.7 psf higher than that.
FIPS 17201, population 283,790, centered near 42.3374°N 89.1612°W. ASCE 7's underlying ground snow load here is 25 psf before the code's exposure and importance factors bring it to the 20 psf design figure above.
Winnebago County: average annual snowfall
Winnebago County sees about 38 in. of snow most winters, per the ROSCOE 2 SE, IL US station's 1991-2020 NOAA normal. See the density guide.
Read this before you use Winnebago 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.