Charles County, MD Roof Snow Load - 20 psf
Charles County, MD roof snow load, translated
A typical heated home in Charles 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. Modern-code homes carry a load like this without issue; an older addition, a carport, or any flat-roofed section is where it is worth checking first.
Charles County in numbers
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map25 psf
- National rank#599 of 2,758
- Maryland rank#10 of 21
- Population174,478
- Annual snowfall, NOAA normal13.4 in.
- FIPS24017
Where Charles County ranks
#10 of 21 Maryland counties by design load, top 22% of 2,758 nationally - that's Charles County's spot. That's 0.1 psf below Maryland's own county-average design load of 20.1 psf.
FIPS 24017, population 174,478, centered near 38.4729°N 77.0154°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.
Charles County: average annual snowfall
Charles County sees about 13.4 in. of snow most winters, per the FRANCONIA 1.3 SSE, VA US station's 1991-2020 NOAA normal. See the density guide.
Read this before you use Charles 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.