Mercer County, PA Roof Snow Load - 20 psf
Mercer County, PA: your roof's ASCE 7 snow number, in plain English
Mercer County's roofs are built to hold 20 psf of snow, the ASCE 7-22 figure a permit reviewer checks first. The physics-based figure alone would be 17.5 psf, but ASCE 7's own low-slope minimum (§7.3.4) sets a floor of 20 psf for flat and low-pitch roofs here, which is the number that actually governs.
In depth, not weight: that's roughly 44 inches of fresh, light snow, 16 inches of old, settled snow, or as little as 4 inches of solid ice - snow that heavy is rare here but ice from a freeze-thaw cycle adds up far faster than the depth suggests. 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.
Got real snow on a Mercer County roof right now?
Mercer County in numbers
- Design roof snow load20 psf
- Ground snow load, ASCE 7 map25 psf
- National rank#642 of 2,758
- Pennsylvania rank#33 of 38
- Population108,140
- Annual snowfall, NOAA normal27.5 in.
- FIPS42085
Mercer County by the numbers
Nationally that's #642 out of 2,758 rated counties, the top 23%; within Pennsylvania alone, Mercer County ranks #33 of 38. 20.9 psf is Pennsylvania's typical county figure - Mercer County comes in 0.9 psf under it.
Mercer County, FIPS 42085, is home to 108,140 people near 41.3°N 80.2528°W. Its 25 psf ground snow load figure is the map value; 20 psf is what a roof is actually designed for.
Mercer County's snowfall, most winters
27.5 in. a year: that's Mercer County's NOAA 1991-2020 snowfall normal, measured at NEW CASTLE 1 N, PA US (20.3 mi away). See the density guide.
Before you rely on Mercer County's number
Treat the Mercer County figure as a starting point, not a final answer: it assumes standard occupancy, a heated structure and a moderately sheltered site, per ASCE 7-22's own defaults. Exposed terrain, an unheated building or a steeper roof all shift the real number.
For a real application, skip the county number and go straight to the ASCE 7 Hazard Tool - enter your coordinates and it returns a site-specific figure a plan reviewer will recognize. Details: the calculation guide.