Philadelphia County, PA Roof Snow Load - 20 psf
What ASCE 7 says about snow load in Philadelphia County
That's Philadelphia County's design roof snow load per ASCE 7-22, for a typical heated single-family home - the number a permit reviewer starts from. 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.
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.
Philadelphia County, PA: quick facts
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map25 psf
- National rank#501 of 2,758
- Pennsylvania rank#25 of 38
- Population1,573,916
- Annual snowfall, NOAA normal16.1 in.
- FIPS42101
Where Philadelphia County's figure sits nationally
Out of 2,758 rated US counties, Philadelphia County sits at #501, the top 18% nationally - #25 of 38 within Pennsylvania. That's 0.9 psf below Pennsylvania's own county-average design load of 20.9 psf.
Near 40.0094°N 75.1333°W, FIPS 42101: Philadelphia County counts 1,573,916 residents and a 25 psf map value, which the code's own factors turn into 20 psf.
How much it actually snows in Philadelphia County
Most winters bring Philadelphia County roughly 16.1 in. of snow - NOAA's normal at PHILA FRANKLIN INST, PA US, 4.1 mi off. (fresh vs. packed vs. ice explains why.)
Read this before you rely on it
Philadelphia 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 Philadelphia County's county-wide figure. Details: the calculation guide.