Washington County, OR Roof Snow Load - 10 psf
Washington County, OR roof snow load, translated
A typical heated home in Washington 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 Washington 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. Standard residential construction handles a load this size without extra bracing; it is a modest addition on top of ordinary roof loading.
Washington County in numbers
- Design roof snow load10 psf
- Ground snow load, ASCE 7 map10 psf
- National rank#1,653 of 2,758
- Oregon rank#6 of 15
- Population611,272
- Annual snowfall, NOAA normal2.7 in.
- FIPS41067
Where Washington County ranks
#6 of 15 Oregon counties by design load, top 60% of 2,758 nationally - that's Washington County's spot. Oregon counties average 12 psf; Washington County runs 2 psf lower than that.
FIPS 41067, population 611,272, centered near 45.5535°N 123.0976°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.
Washington County: average annual snowfall
Washington County sees about 2.7 in. of snow most winters, per the FOREST GROVE, OR US station's 1991-2020 NOAA normal. See the density guide.
Read this before you use Washington 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. See the methodology guide.