Minnesota does not leave frost depth to the local building department: state rule fixes the footing depth at five feet across the northern third of the state and three and a half feet everywhere else, and MnDOT measures how deep the ground actually freezes each winter.
42 to 60 inches
Minnesota's code carries a frost line depth table: 2 zones, running 42 to 60 inches.
In the absence of a determination by an engineer competent in soil mechanics, the minimum allowable footing depth in feet due to freezing is five feet in Zone I and 3-1/2 feet in Zone II.1303.1600 Footing Depth for Frost Protection, Minnesota Office of the Revisor of Statutes, read September 22, 2026. Read it at the source
The table in full. A jurisdiction may amend upward, so a town’s own figure can be deeper than the row below, never shallower.
| Zone | Frost line depth |
|---|---|
| Zone I (Aitkin, Becker, Beltrami, Carlton, Cass, Clay, Clearwater, Cook, Crow Wing, Douglas, Grant, Hubbard, Itasca, Kanabec, Kittson, Koochiching, Lake, Lake of the Woods, Mahnomen, Marshall, Mille Lacs, Morrison, Norman, Otter Tail, Pennington, Pine, Polk, Red Lake, Roseau, St. Louis, Todd, Traverse, Wadena, Wilkin) | 5 feet |
| Zone II (Anoka, Benton, Big Stone, Blue Earth, Brown, Carver, Chippewa, Chisago, Cottonwood, Dakota, Dodge, Faribault, Fillmore, Freeborn, Goodhue, Hennepin, Houston, Isanti, Jackson, Kandiyohi, Lac qui Parle, Le Sueur, Lincoln, Lyon, McLeod, Martin, Meeker, Mower, Murray, Nicollet, Nobles, Olmsted, Pipestone, Pope, Ramsey, Redwood, Renville, Rice, Rock, Scott, Sibley, Sherburne, Stearns, Steele, Stevens, Swift, Wabasha, Waseca, Washington, Watonwan, Winona, Wright, Yellow Medicine) | 42 inches |
A frost line depth turns into two separate requirements in most codes: how far a footing has to bear below grade, and how far a buried water service has to sit below the same line. Minnesota writes both of them out.
Minnesota sets the footing depth directly by zone rather than by a mapped frost line: five feet in the northern Zone I counties and three and a half feet in the southern Zone II counties, unless a soils engineer justifies less.
In the absence of a determination by an engineer competent in soil mechanics, the minimum allowable footing depth in feet due to freezing is five feet in Zone I and 3-1/2 feet in Zone II.1303.1600 Footing Depth for Frost Protection, Minnesota Office of the Revisor of Statutes, read September 22, 2026. Read it at the source
The state plumbing code ties buried water piping to the local frost depth rather than to one statewide number: it must sit at least 12 inches below the maximum local frost depth, and never less than 12 inches below finish grade.
Building supply and yard piping shall be located not less than 12 inches (305 mm) below the maximum local frost depth, in accordance with section 312.6, or an alternative approved by the Authority Having Jurisdiction.4714.0609 Installation, Testing, Unions, and Location, Minnesota Office of the Revisor of Statutes, read September 22, 2026. Read it at the source
A code depth is a design figure. Minnesota is unusual in also measuring the real thing: MnDOT instruments roadbeds at sixteen sites around the state and publishes frozen soil profile graphs showing how deep frost has driven and how far thaw has come back up, through the winter and spring load restriction season.
These graphs display frozen soil profiles derived from sensor data.Frost and Thaw Depths, Seasonal Load Limits, Minnesota Department of Transportation, read September 22, 2026. Read it at the source
The air freezing index is the quantity the frost provisions of the model codes are written on: add up how far each day’s mean temperature fell below freezing over a winter, in degree days, and take the deepest run the winter managed. It measures how much cold the ground had to absorb, which is why it is the honest way to set one place beside another. International Falls is the coldest of the 3 cities on the record in Minnesota.
2,783degree days
average freezing index a winter
Intl Falls Intl AP
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| International Falls | Minnesota | 2,783 | 4,569 | 198 |
| Duluth | Minnesota | 2,174 | 3,649 | 182 |
| Minneapolis | Minnesota | 1,492 | 2,889 | 152 |
Computed from NOAA National Centers for Environmental Information, Global Historical Climatology Network daily temperature records for each station, from 1951 onward. These are measurements of winter, not depths.
Only a handful of states answer with one number for the whole state, and they are the only codes that can be set beside each other directly. Ranked by the freezing index at their own reference cities, with Minnesota marked at 2,150 degree days for comparison alongside what those codes settled on:
Left to right, the mildest winters to the hardest. The figure on the right is what that state wrote into its code.
The nearest by winter are Wisconsin at 4 feet, Vermont at 5 feet and Michigan at 42 inches. That is a reading of other states’ codes rather than a depth for an address in Minnesota: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
Minnesota code read September 22, 2026 from 1303.1600 Footing Depth for Frost Protection, Minnesota Office of the Revisor of Statutes. Codes are amended and a local amendment can be deeper than the state figure, so the building department issuing the permit has the number that binds. Every state is on the frost line depth hub.