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Frost data
Frost line depth in Michigan
The short answer
Michigan publishes a code frost depth of 42 in. Michigan writes 42 inches into the state residential code itself, one figure for the whole state, upper peninsula included. Footings have to bear below that depth, and a water service line has to sit at least six inches below it and at least twelve inches down, which in Michigan works out to a minimum of 48 inches. Source: Michigan LARA, 2021 Michigan Residential Code, Rule 516 (R 408.30516) amending Table R301.2(1); frost line depth 42 in. Filed 2025-05-01, effective 2025-08-29.
Rule 516 of the 2021 Michigan Residential Code amends the model climate table and fills the frost-line cell with 42 inches statewide. It took effect in August 2025 and it applies from Monroe to Copper Harbor without zones or exceptions, which is unusual for a state that spans six degrees of latitude and two peninsulas.
A single figure has an obvious cost and a real benefit. The cost is that 42 inches is generous for the southern tier and tight against the northern winter. The benefit is that a builder, an inspector and a homeowner in Michigan are all working from the same number, which is more than can be said in most of the country.
Michigan has not amended the water service depth rule, so the model-code language governs and the state frost figure sets the floor: a service line goes at least six inches below 42 inches, which is four feet.
The weather behind the number
When it freezes in Michigan
NOAA 1991 to 2020 normals at representative stations across the state.
| Station | First 32°F | First 28°F | First 20°F | Last 32°F | Nights below 20°F |
|---|---|---|---|---|---|
| ALPENA CO RGNL AP | October 1 | October 15 | November 11 | May 17 | 81 |
| GLADWIN | October 4 | October 17 | November 14 | May 9 | 76 |
| GRAND RAPIDS | October 20 | November 2 | November 27 | April 29 | 52 |
| HANCOCK HOUGHTON CO AP | October 1 | October 14 | November 11 | May 17 | 93 |
| MUNSING LAKESHORE | October 10 | October 27 | November 18 | May 23 | 77 |
| PORT HOPE | November 3 | November 14 | December 5 | April 28 | 48 |
Dates are the median: half of years cross that threshold earlier, half later. “no normal” means NOAA publishes none for that station, which at a warm station means it does not reliably get that cold. Source: NOAA NCEI U.S. Climate Normals, 1991-2020, retrieved 2026-09-09.
Across all 211 Michigan stations with published normals, the median first 32°F night falls around October 11 and the median station records 69 nights a year below 20°F, which is the coldest threshold NOAA counts and a decent proxy for a hard freeze rather than a light frost. The state’s spread runs from AMASA 1W, where the median first freeze is September 9, to S HAVEN at November 5.
Michigan’s median station crosses freezing around 11 October and records about 69 nights a year below 20°F. The Great Lakes make its internal pattern unusual: Amasa, inland in the western upper peninsula, reaches its median first freeze on 9 September, while South Haven on the Lake Michigan shore holds out until 5 November, almost two months later. Lake effect keeps the shoreline mild in autumn and then buries it in snow, so shoreline counties and inland counties experience the same 42-inch rule very differently.
Water lines
Burial depth for a water service line in Michigan
Michigan does not amend the model rule for water service depth, so the code language applies: water service pipe not less than 12 inches deep and not less than 6 inches below the frost line, which against the state's 42-inch frost depth puts the minimum at 48 inches.
Under the model rule that Michigan works from, a water service line goes Water service pipe shall be installed not less than 12 inches (305 mm) deep and not less than 6 inches (152 mm) below the frost line.
which puts the floor here at 48 inches. 2021 International Residential Code, Section P2603.5 (Freezing), ICC free code viewer. Your water utility may specify more for the portion of the service it owns, and the building department that issues the permit has the final say. The national picture is on how deep water lines are buried.
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Common questions
Michigan frost line questions
How deep is the frost line in Michigan?
Forty-two inches statewide. Michigan is one of a small number of states that fills in the frost-line cell of the residential code climate table itself rather than leaving it to local jurisdictions, and Rule 516 of the 2021 Michigan Residential Code sets it at 42 inches everywhere.
Does the upper peninsula have a deeper frost line than Detroit?
Not in code. The 42-inch figure is statewide and carries no zone adjustment for the upper peninsula, which is unusual among the northern states; Minnesota, by contrast, splits into 42-inch and 60-inch zones. The weather is certainly different, and a local jurisdiction may impose more through its own amendments, so it is still worth confirming with the building department that issues your permit.
Next
Where to go from here
The frost depth is the digging number. It won’t tell you whether your pipes are at risk this winter, and the two pages that will are at what temperature pipes freeze and when pipes freeze where you live, both with a ZIP lookup. If a pipe has already split, burst pipe repair cost covers the repair and the water damage behind it, and what to do about a frozen pipe is the page to open first.
Other state pages: Minnesota, Iowa, Ohio, Indiana, Illinois, Virginia, Wisconsin, Missouri, and all fifty in the national table.
Where these numbers come from
The Michigan frost figure was researched against the body that publishes it, and it’s recorded with a confidence note of “state rule, verified” in our source ledger. Freeze dates are NOAA normals for stations in the state, picked by a fixed rule rather than by hand: first-order stations, spread west to east. The full method is on our methodology page.
- Freeze dates and cold-night counts: NOAA NCEI U.S. Climate Normals, 1991 to 2020, annual and seasonal by station. Retrieved 2026-09-09. Field definitions are in the by-variable readme.
- ZIP code locations: U.S. Census Bureau 2023 ZIP Code Tabulation Area gazetteer, matched to the nearest station by great-circle distance.
- Michigan LARA, 2021 Michigan Residential Code, Rule 516 (R 408.30516) amending Table R301.2(1); frost line depth 42 in. Filed 2025-05-01, effective 2025-08-29 The Michigan frost depth figure and basis.
- 2021 International Residential Code, Section P2603.5 (Freezing), ICC free code viewer The water service line burial rule.
The full method, including how we pick a station and what we do when there is not one close enough, is on our methodology page.
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