Frost Line Depth in Minnesota
Two code zones: 60 inches in the north, 42 inches in the Twin Cities and the south
Written by M., a general contractor in Richmond, VA · Last updated · Reviewed against the current Minnesota State Building Code (Rules 1303.1600)
How Deep Is the Frost Line in Minnesota?
Minnesota has two code frost depths. Zone I, the northern half of the state including Duluth, Brainerd, Bemidji, Moorhead and St. Cloud, requires footings 60 inches below grade. Zone II, the Twin Cities metro and southern Minnesota including Rochester, Mankato, Red Wing and Winona, requires 42 inches. The zones are set by Minnesota Rules 1303.1600 with a county map published by the Department of Labor and Industry, and they apply wherever the State Building Code is enforced.
| State | Avg. Depth (in.) | Range (in.) | Major City Examples | Code basis |
|---|---|---|---|---|
| Minnesota | 80 | 42 - 80 | Minneapolis, St. Paul, Rochester | Minnesota Rules 1303.1600: Zone I 60 in, Zone II 42 in |
Returns the code depth for the nearest listed city and the regional note for that part of the state. A ZIP outside Minnesota still resolves to its own state.
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All 50 states and the national map are on the frost line depth by ZIP code page. Footing width comes from the footing size chart and soil bearing capacity; roof loads from snow load by ZIP code.
What the Minnesota Code Says
Minnesota adopts the IRC as part of the Minnesota State Building Code (Minnesota Rules Chapter 1309) and amends the frost protection provision in Chapter 1303, the state's "Minnesota Provisions." Minnesota Rules 1303.1600 divides the state into two zones on a county map maintained by the Department of Labor and Industry. In Zone I (the northern and central counties) footings and foundations must extend at least 60 inches below grade; in Zone II (the metro and southern counties) the minimum is 42 inches. The rule applies to all buildings under the State Building Code, including decks and detached garages that exceed the accessory exemption.
The zone line runs roughly from the South Dakota border near Ortonville northeast through the Lake Mille Lacs area to the Wisconsin border near Pine City. Everything north of that line, including Duluth, the Iron Range, Brainerd, Bemidji, Fergus Falls, Moorhead and St. Cloud, is Zone I at 60 in. The seven-county Twin Cities metro, Rochester, Mankato, Winona, Red Wing, Owatonna, Marshall and Worthington are Zone II at 42 in. A handful of counties on the line (Stearns, Kanabec, Isanti, Chisago) sit at the boundary; check the DLI map for your parcel rather than assuming.
The State Building Code is mandatory in every city and in counties that have adopted it; rural townships in some counties have not adopted the code and issue no building permits, but 1303.1600 is still the standard lenders and insurers expect. Minnesota also allows frost-protected shallow foundations under IRC R403.3 and ASCE 32 for heated buildings, which is popular in Zone I where a 60 in frost wall is expensive, and it exempts freestanding accessory structures of 600 sq ft or less from frost protection. The 60 in Zone I depth is the deepest statewide code value in the lower 48, matched only by North Dakota and northern Maine municipalities; see the national table for the comparison.
Frost Depth Zones in Minnesota
The two zones come straight from Minnesota Rules 1303.1600 and the DLI county map. Counties on the boundary are listed so you can check the map for your parcel.
| Zone or region | Footing depth | Where it applies |
|---|---|---|
| Zone I (north and central) | 60 in | Duluth, Iron Range, Brainerd, Bemidji, Grand Rapids, International Falls, Moorhead, Fergus Falls, Alexandria, St. Cloud, Little Falls; all counties north of the Mille Lacs line |
| Zone II (metro and south) | 42 in | Minneapolis, St. Paul and the 7-county metro, Rochester, Mankato, Winona, Red Wing, Faribault, Owatonna, Marshall, Worthington, Albert Lea |
| Boundary counties (check the DLI map) | 42 or 60 in by county | Stearns, Sherburne, Isanti, Chisago, Kanabec, Pope, Stevens, Big Stone |
Minnesota Frost Line Depth by City and County
Cities are listed with their zone under Minnesota Rules 1303.1600. The county determines the zone; a city on the line follows its county.
| City | County | Required Footing Depth (in.) | Source |
|---|---|---|---|
| Minneapolis | Hennepin | 42 | Minnesota Rules 1303.1600 Zone II |
| St. Paul | Ramsey | 42 | Minnesota Rules 1303.1600 Zone II |
| Rochester | Olmsted | 42 | Minnesota Rules 1303.1600 Zone II |
| Duluth | St. Louis | 60 | Minnesota Rules 1303.1600 Zone I |
| Bloomington | Hennepin | 42 | Minnesota Rules 1303.1600 Zone II |
| Brooklyn Park | Hennepin | 42 | Minnesota Rules 1303.1600 Zone II |
| Mankato | Blue Earth | 42 | Minnesota Rules 1303.1600 Zone II |
| St. Cloud | Stearns | 60 | Minnesota Rules 1303.1600 Zone I (boundary county; verify on the DLI map) |
| Moorhead | Clay | 60 | Minnesota Rules 1303.1600 Zone I |
| Brainerd | Crow Wing | 60 | Minnesota Rules 1303.1600 Zone I |
| Bemidji | Beltrami | 60 | Minnesota Rules 1303.1600 Zone I |
| Red Wing | Goodhue | 42 | Minnesota Rules 1303.1600 Zone II |
| Winona | Winona | 42 | Minnesota Rules 1303.1600 Zone II |
| International Falls | Koochiching | 60 | Minnesota Rules 1303.1600 Zone I |
| Hibbing | St. Louis | 60 | Minnesota Rules 1303.1600 Zone I |
Depth is from finished grade to the bottom of the footing. Municipalities may not reduce the rule value, and the DLI zone map controls where a county sits on the boundary.
Decks, Fences and Water Lines in Minnesota
- - Deck footings: Any deck attached to the house must bear below the frost line, so piers go to 42 (Zone II) or 60 (Zone I) in or deeper. Freestanding decks under the IRC R403.1.4.1 size limit may sit on pier blocks if the local inspector allows it. Zone I builders often switch to helical piers because a 60 in hand-dug hole is impractical. Size the pier with the deck footing size chart.
- - Fence posts: Code rarely requires frost depth for a fence that carries no structure, but posts set shallower than the frost line heave and lean within a few winters in Minnesota. Use one third of the post height with a minimum of 24 in, and go to 42 (Zone II) or 60 (Zone I) in for gate and corner posts. In Zone I, a 6 ft privacy fence is typically set 48 in with 60 in gate posts. Bag counts are in the post hole bags guide.
- - Water lines: IRC P2603.5 puts exterior water service at least 6 in below the frost line and never shallower than 12 in, so the code floor here is 48 in in Zone II and 66 in in Zone I (frost depth + 6). Many Minnesota utilities require more; check the water department standard before trenching and call 811 first.
Neighboring states: Wisconsin (48 in), Iowa (42 in), North Dakota (48 in typical), South Dakota (48 in typical). When a project sits near a state line, the permit follows the jurisdiction where the footing is, not where the contractor is based.
Frequently Asked Questions
What is the frost line depth in Minnesota?
60 inches in Zone I (the northern half of the state, including Duluth, Brainerd, Bemidji, Moorhead and St. Cloud) and 42 inches in Zone II (the Twin Cities metro and southern Minnesota, including Rochester, Mankato and Winona), per Minnesota Rules 1303.1600.
What is the frost line in Minneapolis and St. Paul?
42 inches. Hennepin, Ramsey and the rest of the seven-county metro are Zone II. Some metro cities historically enforced 48 in; the state rule now controls at 42.
Is St. Cloud Zone I or Zone II?
Stearns County is on the zone boundary and the DLI map places St. Cloud in Zone I at 60 in. Because Sherburne and Benton counties share the metro area, verify your specific parcel on the DLI frost depth map before designing.
How deep do deck footings have to be in Minnesota?
42 in in Zone II and 60 in in Zone I for any attached deck. Freestanding decks under the 600 sq ft accessory exemption may use pier blocks where the city allows. In Zone I most contractors use helical piers or a power auger for 60 in holes.
How deep are water lines buried in Minnesota?
The code floor is the frost depth plus 6 in, but Minnesota utilities require much more: Minneapolis and St. Paul specify 7 ft (84 in) to the top of the service, and Duluth and Iron Range cities 8 ft. Always use the utility standard.
Can I use a frost-protected shallow foundation in Zone I?
Yes, for a heated building designed under ASCE 32 and IRC R403.3. Minnesota's air freezing indices exceed 3,000 in the north, so the insulation wings are wider and thicker than in southern states, but the savings over a 60 in frost wall are large.
Sources
- Minnesota Rules 1303.1600: Zone I 60 in, Zone II 42 in. Retrieved September 27, 2026.
- Minnesota Office of the Revisor of Statutes. Minnesota Rules 1303.1600, Footing Depth for Frost Protection. Retrieved September 27, 2026.
- Minnesota Department of Labor and Industry. Frost Depth Zone Map. Retrieved September 27, 2026.
- International Code Council. 2024 International Residential Code, Table R301.2(1), R403.1.4 and R403.1.4.1. codes.iccsafe.org.
- National Weather Service, North Central River Forecast Center. Frost Depth Map. weather.gov.
City values are the frost line or minimum footing depths published or applied by each jurisdiction as of the retrieval date. Codes change on a three-year cycle and local amendments change between cycles; confirm with the building department before you submit a permit.