Madison County, IA Roof Snow Load - 20 psf
Madison County, IA roof snow load, translated
A typical heated home in Madison County is designed to carry 20 pounds per square foot of snow on its roof, per ASCE 7-22. 14 psf is what the ground-load formula alone gives; Madison County's 20 psf low-slope minimum (§7.3.4) beats it, so that figure is the one that governs on flat and low-pitch roofs.
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. A meaningful design load. Most homes built to modern code handle it, but additions, carports, and flat-roofed sections are worth a second look.
Madison County in numbers
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map20 psf
- National rank#988 of 2,758
- Iowa rank#69 of 99
- Population17,161
- Annual snowfall, NOAA normal30.7 in.
- FIPS19121
Where Madison County ranks
#69 of 99 Iowa counties by design load, top 36% of 2,758 nationally - that's Madison County's spot. Iowa counties average 21.7 psf; Madison County runs 1.7 psf lower than that.
FIPS 19121, population 17,161, centered near 41.3306°N 94.0152°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.
Madison County: average annual snowfall
Madison County sees about 30.7 in. of snow most winters, per the WINTERSET 1S, IA US station's 1991-2020 NOAA normal. See the density guide.
Read this before you use Madison 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. Details: the calculation guide.