New Jersey Frost Depth: 30 Inches South, 36 Inches North

New Jersey does not leave the frost line depth to each municipality. The Department of Community Affairs writes the values straight into the adopted residential subcode and then deletes the model code's instruction to fill the column in locally. Two zones are defined. SNJ, which is Monmouth and Burlington counties and all counties to the south, takes 2 feet 6 inches, 30 inches. NNJ, which is Mercer and Middlesex counties and all counties to the north, takes 3 feet, 36 inches. Note that the code states them in feet and inches, not inches, so a drawing calling for a 30-inch footing in Bergen County is six inches short of the adopted requirement. New Jersey deliberately removed the sentence directing the jurisdiction to fill in the frost line depth column, which is what makes these figures statewide rather than a starting point for local variation.

Footing depth is verified at the foundation inspection before concrete is placed, by the local enforcing agency under the Uniform Construction Code. A footing shallower than the zone value will not pass. The zone boundary runs between Middlesex and Monmouth on the coast side, so builders working near that line need to confirm which county the site is actually in rather than which one is nearest.