Frost Line Depth in Minnesota
- 10 verified values
- 10 places covered
- Checked Oct 2026
Verified range
42–60 in across Minnesota
Minnesota sets frost line depth by county or zone in its state code.
State document: revisor.mn.gov
How deep is the frost line in Minnesota?
Minnesota sets frost line depth in its state code by zone: 60 (Zone I) / 42 (Zone II) inches. Find your county in the table below; the deeper value applies in the colder part of the state.
Who sets the frost line depth in Minnesota?
The depth is written into Minnesota’s statewide residential code, so local building departments enforce the state’s number rather than choosing their own. The quoted text below is the rule as we read it.
“1303.1600 FOOTING DEPTH FOR FROST PROTECTION ... Zone I five feet; Zone II 3-1/2 feet ... Slab on grade construction may be placed on any soil except peat or muck for detached one-story private garage, carport, and shed buildings not …”
State document: revisor.mn.gov, read October 2026.
Which Minnesota buildings can skip frost footings?
Minnesota Rule 1303.1600 splits the state into Zone I, at 5 feet (60 inches), and Zone II, at 3½ feet (42 inches), and lists the counties in each. It also allows a slab on grade, not on peat or muck, for a detached one-story garage, carport or shed of 1,000 square feet or less. That is broader than the model code’s 600 square foot exemption for accessory buildings.
Frost line depth in Minnesota cities and counties
Every Minnesota place we cover, largest first. Verified values come from the place’s own code or the state rule; the others show nearby official values and who to ask.
| Place | Frost line | Type |
|---|---|---|
| St. Louis County | 60 in (Minnesota rule) | County |
| Stearns County | 42 in (Minnesota rule) | County |
| Rochester | 42 in (Minnesota rule) | City |
| Maple Grove | 42 in (Minnesota rule) | City |
| Crow Wing County | 60 in (Minnesota rule) | County |
| Eagan | 42 in (Minnesota rule) | City |
| Otter Tail County | 60 in (Minnesota rule) | County |
| Winona County | 42 in (Minnesota rule) | County |
| St. Louis Park | 42 in (Minnesota rule) | City |
| Itasca County | 60 in (Minnesota rule) | County |
How deep do footings need to be in Minnesota?
Exterior footings go at least 12 inches below undisturbed ground and below the depth the state code sets for your county, measured to the bottom of the footing. The residential code (IRC R403.1.4.1) also accepts a frost-protected shallow foundation, a design to ASCE 32 or solid rock in place of digging to the frost line, and it exempts small free-standing accessory buildings: light-frame ones up to 600 square feet with eaves 10 feet high or lower. Minnesota may amend these rules, so confirm them with your building department. More detail: footing depth.
How deep should deck footings and fence posts be in Minnesota?
A deck attached to the house needs footings below the depth the state code sets for your county. Under the 2021 and 2024 IRC a free-standing deck needs footings only 12 inches deep, and the 2018 edition exempts free-standing decks from the frost rule, so the answer depends on the edition Minnesota adopted. See deck footing depth.
The residential code sets no fence-post depth, and fences up to 7 feet tall are exempt from a building permit (IRC R105.2), though zoning still applies. A common practice is to bury about half the above-ground height, and to reach the frost line when posts are set in concrete. See fence post depth.
How deep are water lines buried in Minnesota?
Under the IRC plumbing rule (P2603.5), a water service line goes at least 12 inches deep and at least 6 inches below the frost line. Minnesota’s plumbing rules (4714.0609) instead require 12 inches below the maximum local frost depth. See water line depth.
How cold do Minnesota winters get?
Across the 10 Minnesota places we track, nights at or below 32 °F range from 139 a year in Winona County to 192 in Itasca County. The average low in the coldest month runs from -4.7 °F in Itasca County to 10.7 °F in Winona County (NOAA 1991–2020 normals, nearest station). Colder winters drive frost deeper in a hard year, but the code depth does not change with the weather. See frost penetration depth.
How do Minnesota soils affect frost heave?
The USDA soil survey rates how prone soil is to frost action. Around the 10 Minnesota places we sampled, the main rating is moderate at 5 places, high at 3 places and low at 2 places. Fine, wet soils rated moderate or high heave the most, so drainage and clean gravel backfill matter more there. The rating does not change the code depth. See frost heave.
How do you confirm the frost line with your Minnesota building department?
- Find your city or county in the table above, or enter your ZIP code; a ZIP can cross into a second county.
- Ask the building department what frost line depth it uses for Table R301.2, measured to the bottom of the footing, and whether it has local rules for decks, sheds or fences.
- Ask the plumbing inspector how deep water and sewer lines must go.
- Call Gopher State One Call a few days before you dig so buried utilities are marked.