Prairie County, MT Roof Snow Load - 20 psf
Prairie County, MT roof snow load, translated
A typical heated home in Prairie County is designed to carry 20 pounds per square foot of snow on its roof, per ASCE 7-22. ASCE 7's low-slope-roof minimum (§7.3.4) raises the governing figure to 20 psf - higher than the 17.5 psf the ground-load formula alone would give, and the code says use the larger one.
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.
Prairie County in numbers
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map25 psf
- National rank#1,289 of 2,758
- Montana rank#21 of 29
- Population1,112
- Annual snowfall, NOAA normal10.8 in.
- FIPS30079
Where Prairie County ranks
#21 of 29 Montana counties by design load, top 47% of 2,758 nationally - that's Prairie County's spot. Montana counties average 19 psf; Prairie County runs 1 psf higher than that.
FIPS 30079, population 1,112, centered near 46.8124°N 105.5039°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.
Prairie County: average annual snowfall
Prairie County sees about 10.8 in. of snow most winters, per the HOYT 2 WSW, MT US station's 1991-2020 NOAA normal. 29.6 mi is a real gap between Prairie County and its nearest reporting station, so local snowfall can diverge from this figure, especially near elevation changes. See the density guide.
Read this before you use Prairie 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.