Pennsylvania adopts the 2021 International Residential Code as its statewide Uniform Construction Code and writes no frost depth of its own, so the frost line number a footing must reach is the one the municipality or third party agency enforcing the code in your area fills into the code's design criteria table.
Pennsylvania leaves the frost line depth to the local building department, which is where the number for an address comes from.
The Department adopts and incorporates by reference the following codes as the Uniform Construction Code: ... (7) The ‘‘International Residential Code of 2021,’’ except that:34 Pa. Code 403.21. Uniform Construction Code, Pennsylvania Code, read September 23, 2026. Read it at the source
That makes the building department issuing the permit the office with the number, and it is a short call: the counter gives the depth for the address, and the same call settles whether a deck footing or a slab edge needs a footing inspection before the concrete goes in. What Pennsylvania does publish is below, and it is worth having in hand first.
The air freezing index is the quantity the frost provisions of the model codes are written on: add up how far each day’s mean temperature fell below freezing over a winter, in degree days, and take the deepest run the winter managed. It measures how much cold the ground had to absorb, which is why it is the honest way to set one place beside another. Erie is the coldest of the 3 cities on the record in Pennsylvania.
461degree days
average freezing index a winter
Erie Intl AP
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Erie | Pennsylvania | 461 | 1,294 | 119 |
| Pittsburgh | Pennsylvania | 366 | 1,062 | 117 |
| Philadelphia | Pennsylvania | 148 | 504 | 86 |
Computed from NOAA National Centers for Environmental Information, Global Historical Climatology Network daily temperature records for each station, from 1951 onward. These are measurements of winter, not depths.
Only a handful of states answer with one number for the whole state, and they are the only codes that can be set beside each other directly. Ranked by the freezing index at their own reference cities, with Pennsylvania marked at 325 degree days for comparison against what those codes settled on:
Left to right, the mildest winters to the hardest. The figure on the right is what that state wrote into its code.
The nearest by winter are Massachusetts at 4 feet, Connecticut at 42 inches and North Carolina at 12 inches. That is a reading of other states’ codes rather than a depth for an address in Pennsylvania: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
Pennsylvania code read September 23, 2026 from 34 Pa. Code 403.21. Uniform Construction Code, Pennsylvania Code. Codes are amended and a local amendment can be deeper than the state figure, so the building department issuing the permit has the number that binds. Every state is on the frost line depth hub.