St. Mary's County, MD Roof Snow Load - 20 psf
St. Mary's County, MD roof snow load, translated
A typical heated home in St. Mary's 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 14 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.
St. Mary's County in numbers
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map20 psf
- National rank#633 of 2,758
- Maryland rank#11 of 21
- Population116,469
- Annual snowfall, NOAA normal11.5 in.
- FIPS24037
Where St. Mary's County ranks
#11 of 21 Maryland counties by design load, top 23% of 2,758 nationally - that's St. Mary's County's spot. 20.1 psf is Maryland's typical county figure - St. Mary's County comes in 0.1 psf under it.
FIPS 24037, population 116,469, centered near 38.2231°N 76.5345°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.
St. Mary's County: average annual snowfall
St. Mary's County sees about 11.5 in. of snow most winters, per the CORBIN, VA US station's 1991-2020 NOAA normal. 45.6 mi is a real gap between St. Mary's 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 St. Mary's 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.