Rock Island County, IL Roof Snow Load - 20 psf
How much snow is too much for a roof in Rock Island County, IL?
20 psf: that's what ASCE 7-22 requires a typical heated home's roof in Rock Island County to carry. §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.
Picture it, not just weigh it: 44 in. if it's fresh powder, 16 in. once it settles, or a mere 4 in. if it's ice. 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.
Rock Island County in numbers
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map20 psf
- National rank#622 of 2,758
- Illinois rank#15 of 102
- Population142,731
- Annual snowfall, NOAA normal36.1 in.
- FIPS17161
How Rock Island County compares
20 psf ranks #622 of 2,758 US counties with a mapped snow load (top 23%) - and #15 of 102 in Illinois. 19.3 psf is Illinois's typical county figure - Rock Island County beats it by 0.7 psf.
Population 142,731 (FIPS 17161), roughly 41.4684°N 90.5721°W. The 20 psf ground snow load ASCE 7-22 maps here becomes 20 psf once the code's own design factors are applied.
Typical snowfall in Rock Island County, IL
NOAA's 30-year normal for Rock Island County: 36.1 in. of snow a year, from the MOLINE QUAD CITY INTL AP, IL US station. (fresh vs. packed vs. ice explains why.)
What this Rock Island County figure assumes
This is a county-level reference figure for a typical heated home built to Risk Category II (ordinary residential), on a partially exposed lot - the assumptions ASCE 7-22 itself treats as the default case. A steeper roof, a fully exposed hilltop lot, an unheated structure, or a higher risk category all change the actual number.
Rock Island County's permit office wants an address-specific figure, not this county average - the ASCE 7 Hazard Tool is free, takes under a minute, and outputs a PDF most reviewers accept. See the methodology guide.