NY · set by county and city amendment
How deep do deck footings and fence posts have to go in New York? Below the frost line. Here's the number, and the winter behind it.
The requirement
48″
Footing bottoms in New York must reach 48 inches below grade — the frost line. Across New York it runs roughly 36″–60″ by county.
Reference: 2020 Residential Code of New York State, Table R301.2(1) and Section R403.1.4.1 (frost line depth entry completed by each local jurisdiction per NYS DOS Technical Bulletin TB-1009-RCNYS) (2020 edition). Counties amend their codes — confirm the exact figure with your local building department before you pour.
Depth pre-filled to the New York frost line. The hole bottom has to reach it — a few inches deeper seats the base cleanly below.
| Bag size | Exact | Buy (with spare) |
|---|
The buy column adds a 10% spare margin and rounds up. Running out mid-pour is the one mistake you can't fix.
Long, cold winters freeze the ground 3 to 4 feet deep across most of the state. The Atlantic moderates NYC and Long Island so frost stays shallower there, while the Adirondacks and North Country see some of the deepest ground freezing in the eastern United States.
The depth tracks how much freezing a winter actually delivers. NOAA's Air Freezing Index keeps a running score of how far and how long air temperatures sit below freezing; deeper scores mean deeper frost, and building codes translate that climate record into the footing depth above. Water expands about 9% when it freezes — when that happens under a footing, the ground lifts it. That's frost heave, and it cracks foundations, tilts fence lines, and pops deck piers. Getting below the frost line puts your concrete where the ground never freezes.
The state Uniform Code applies statewide, but each town, city, or village fills in its own frost line depth in Table R301.2(1) using air freezing index, soils, and local history. Roughly 36 in. is typical for NYC and Long Island (NYC enforces its own code), 42-48 in. across upstate, and up to 60 in. in the Adirondack North Country.
Treat this page as the starting number, not the permit. County and city amendments are where the real precision lives, and inspectors enforce the local figure — one phone call to the building department settles it.
48 inches is the working number (set by county and city amendment). Across New York it runs roughly 36″–60″ by county. Confirm the exact figure with your local building department — county amendments are common.
Bury one third of the above-grade height, never less than 24″, and never shallower than the frost line — in New York that means at least 48″. The post depth calculator checks both rules for you.
Below the frost line — 48″ minimum, bearing on undisturbed soil beneath it. Size the diameter with the deck footing calculator, then figure bags with the depth pre-filled above.
Yes — 811 covers every state, and the locate is free. Call a few business days before any post hole or footing dig and crews mark the buried utilities.