Knox County, IL Roof Snow Load - 20 psf
Knox County, IL roof snow load, translated
A typical heated home in Knox 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 14 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. 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.
Knox County, IL: quick facts
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map20 psf
- National rank#738 of 2,758
- Illinois rank#27 of 102
- Population48,716
- Annual snowfall, NOAA normal25.4 in.
- FIPS17095
Where Knox County ranks
#27 of 102 Illinois counties by design load, top 27% of 2,758 nationally - that's Knox County's spot. 19.3 psf is Illinois's typical county figure - Knox County beats it by 0.7 psf.
FIPS 17095, population 48,716, centered near 40.9309°N 90.2138°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.
Knox County: average annual snowfall
Knox County sees about 25.4 in. of snow most winters, per the KNOXVILLE, IL US station's 1991-2020 NOAA normal. See the density guide.
Read this before you use Knox 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. (How this figure is calculated.)