Ada County, ID Roof Snow Load - 10 psf
Ada County, ID roof snow load, translated
A typical heated home in Ada County is designed to carry 10 pounds per square foot of snow on its roof, per ASCE 7-22. Flat and low-pitch roofs in Ada County are actually governed by ASCE 7's §7.3.4 minimum of 10 psf, not the 7 psf the ground-load formula alone would produce.
On a roof that means 22 in. of fresh snow, 8 in. once it packs down, or 2 in. of solid ice - three very different piles for the same load. A modest addition to standard roof loading. Ordinary residential construction handles this without extra bracing.
Snow on Ada County's roofs right now?
Ada County, ID: quick facts
- Design roof snow load10 psf
- Ground snow load, ASCE 7 map10 psf
- National rank#1,655 of 2,758
- Idaho rank#3 of 9
- Population535,799
- Annual snowfall, NOAA normal17.6 in.
- FIPS16001
Where Ada County ranks
#3 of 9 Idaho counties by design load, top 60% of 2,758 nationally - that's Ada County's spot. 12.2 psf is Idaho's typical county figure - Ada County comes in 2.2 psf under it.
FIPS 16001, population 535,799, centered near 43.4515°N 116.2444°W. ASCE 7's underlying ground snow load here is 10 psf before the code's exposure and importance factors bring it to the 10 psf design figure above.
Ada County: average annual snowfall
Ada County sees about 17.6 in. of snow most winters, per the BOISE AIR TERMINAL, ID US station's 1991-2020 NOAA normal. See the density guide.
Read this before you use Ada 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.