Frost line depth in Berks County, PA
How deep the ground freezes in Berks County, PA
19 in. Dig to 20 in, just below the frost. Nearest NOAA station: Reading 4 Nnw, 0.9 mi.
Your building department sets the legal frost line depth (IRC Table R301.2(1)); footings must go below it (R403.1.4.1). Call them before you dig.