MN · statewide code figure
How deep do deck footings and fence posts have to go in Minnesota? Below the frost line. Here's the number, and the winter behind it.
The requirement
60″
Footing bottoms in Minnesota must reach 60 inches below grade — the frost line. Across Minnesota it runs roughly 42″–60″ by county.
Reference: Minnesota Rules, part 1303.1600 (Minnesota State Building Code), Footing Depth for Frost Protection (2020 edition). Counties amend their codes — confirm the exact figure with your local building department before you pour.
Depth pre-filled to the Minnesota 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.
Minnesota has some of the coldest winters in the lower 48, with long stretches of subzero air that drive frost 4 to 5 feet into exposed ground in the northern counties. The southern half of the state freezes less deeply, which is why the code allows 42 inches there versus 60 inches up north.
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 rule splits Minnesota into two zones: 60 inches in Zone I (34 northern counties including Duluth/St. Louis County) and 42 inches in Zone II (the southern half, including the Twin Cities metro). An engineer competent in soil mechanics may justify a different depth on a specific site.
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.
60 inches is the working number (statewide code figure). Across Minnesota it runs roughly 42″–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 Minnesota that means at least 60″. The post depth calculator checks both rules for you.
Below the frost line — 60″ 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.