Marion County, IL Roof Snow Load - 20 psf
Marion County, IL roof snow load, translated
A typical heated home in Marion County is designed to carry 20 pounds per square foot of snow on its roof, per ASCE 7-22. 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.
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.
Marion County, IL: quick facts
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map20 psf
- National rank#806 of 2,758
- Illinois rank#34 of 102
- Population36,437
- Annual snowfall, NOAA normal14.7 in.
- FIPS17121
Where Marion County ranks
#34 of 102 Illinois counties by design load, top 29% of 2,758 nationally - that's Marion County's spot. Illinois counties average 19.3 psf; Marion County runs 0.7 psf higher than that.
FIPS 17121, population 36,437, centered near 38.6482°N 88.9204°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.
Marion County: average annual snowfall
Marion County sees about 14.7 in. of snow most winters, per the KINMUNDY, IL US station's 1991-2020 NOAA normal. See the density guide.
Read this before you use Marion 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.)