Allegheny County, PA Roof Snow Load - 20 psf
What ASCE 7 says about snow load in Allegheny County
That's Allegheny County's design roof snow load per ASCE 7-22, for a typical heated single-family home - the number a permit reviewer starts from. 17.5 psf is what the ground-load formula alone gives; Allegheny 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.
Converted to something you can actually eyeball on a roof: about 44 in. of fresh powder, 16 in. once it settles and packs down, or just 4 in. if it's turned to ice. 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.
Allegheny County, PA: quick facts
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map25 psf
- National rank#507 of 2,758
- Pennsylvania rank#26 of 38
- Population1,231,814
- Annual snowfall, NOAA normal19.8 in.
- FIPS42003
Where Allegheny County's figure sits nationally
Out of 2,758 rated US counties, Allegheny County sits at #507, the top 18% nationally - #26 of 38 within Pennsylvania. Pennsylvania counties average 20.9 psf; Allegheny County runs 0.9 psf lower than that.
Near 40.4698°N 79.9805°W, FIPS 42003: Allegheny County counts 1,231,814 residents and a 25 psf map value, which the code's own factors turn into 20 psf.
How much it actually snows in Allegheny County
Most winters bring Allegheny County roughly 19.8 in. of snow - NOAA's normal at GLENWILLARD DASHIELDS L&D, PA US, 13 mi off. (fresh vs. packed vs. ice explains why.)
Read this before you rely on it
Allegheny County's number above is ASCE 7-22's default case, not a custom calculation: ordinary residential occupancy, heated, sited on ground that's neither fully sheltered nor fully exposed. Any one of those changing - pitch, exposure, heating, occupancy - moves the real figure.
Nothing here substitutes for an address-level number. Get one free, in about a minute, from the ASCE 7 Hazard Tool using your own coordinates rather than Allegheny County's county-wide figure. Details: the calculation guide.