Johnson County, TN Roof Snow Load - 20 psf
Johnson County, TN roof snow load, translated
A typical heated home in Johnson 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; Johnson 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. 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.
Johnson County at a glance
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map20 psf
- National rank#976 of 2,758
- Tennessee rank#1 of 95
- Population18,506
- Annual snowfall, NOAA normal12 in.
- FIPS47091
Where Johnson County ranks
#1 of 95 Tennessee counties by design load, top 35% of 2,758 nationally - that's Johnson County's spot. Tennessee counties average 10.3 psf; Johnson County runs 9.7 psf higher than that.
FIPS 47091, population 18,506, centered near 36.4532°N 81.8612°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.
Johnson County: average annual snowfall
Johnson County sees about 12 in. of snow most winters, per the MTN CITY 2, TN US station's 1991-2020 NOAA normal. See the density guide.
Read this before you use Johnson 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.