Deck footings

How deep do deck footings need to be in Minnesota?

Short answer: At least 42 inches below grade in 53 counties, including the Twin Cities, Rochester, Mankato and St. Cloud. At least 60 inches in the 34 northern counties, including the Duluth, Brainerd, Bemidji, Alexandria and Moorhead areas.

Source: Minnesota Rules 1303.1600, footing depth for frost protection. Checked November 4, 2026.

Footings sit below the frost line so the ground can't heave the deck in winter. Find your county below.

60 inches: 34 northern counties

42 inches: 53 counties in southern and central Minnesota

The rule calls these Zone I (5 feet) and Zone II (3 1/2 feet). A soils engineer can show that less depth is safe, and then the city may allow it.

Deck footing cross-section A deck post sits on a concrete footing that goes at least 42 inches below grade, below the frost line. 42 in. minimum Deck boards Ledger bolted to the house Beam Post Grade Concrete footing Frost line
Not to scale. In southern Minnesota, including the Twin Cities, footings must reach at least 42 inches below grade so frost can't heave the deck. In the northern counties it is 60 inches. Some cities, like Eagan, want any engineered footing, such as a Diamond Pier, named on the plans.

When the rule applies

Your city's building department has the final word. See permit links for 33 cities, or find a deck builder near you.

Sources: Minnesota Rules 1303.1600, footing depth for frost protection · Bloomington, residential deck handout (PDF) · St. Cloud, deck, screen and covered porch handout (PDF) · Eagan, deck supplement (PDF) · Golden Valley, decks handout (PDF)

Questions

How deep are deck footings in the Twin Cities?

At least 42 inches below grade. Hennepin, Ramsey, Anoka, Dakota, Washington, Scott and Carver counties are all in the 42-inch zone of Minnesota Rules 1303.1600.

How deep are deck footings in Duluth, Brainerd or Moorhead?

At least 60 inches. St. Louis, Crow Wing and Clay counties are among the 34 northern counties where the state sets footings at 5 feet.

Do freestanding decks need frost footings?

Not always. St. Cloud, for example, requires 42-inch footings for an attached deck, while a freestanding deck needs proper footings but not frost depth. Ask your city before you build.

Can I use helical piles or a Diamond Pier instead of concrete?

Often, if your city approves it. Bloomington accepts approved pin foundations for decks but not for screen porches or three-season porches, and Eagan wants any engineered footing named on the plans.

Can footings be shallower than the rule says?

Only with a soils engineer. Minnesota Rules 1303.1600 allows less depth when an engineer competent in soil mechanics shows it is safe.

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