Frost Line Depth in Detroit, MI: 42 in (Michigan rule)

State-set value

42in

107 cm · 3 ft 6 in

42 in (Michigan rule)

Set by the state: Michigan Residential Code R403.1.4 (R 408.30522); the building official may modify.

Source and how we checked

Detroit does not publish its own value; the state rule applies.

Document: codes.iccsafe.org

Climate: 125 nights a year at or below 32 °F (NOAA 1991–2020, Dearborn #2, 4.4 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

125nights a year at or below 32 °F
68%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Detroit?

Michigan sets the frost footing depth for Detroit at 42 in (107 cm). Footings, piers and other permanent supports must reach at least this depth (IRC R403.1.4.1).

Who sets the frost line depth in Detroit?

Michigan writes this depth into its statewide residential code, so Detroit’s building department enforces the state’s number rather than setting its own. Wayne County uses the same 42 in, so the depth does not change at the city limits. See how Michigan sets frost line depth.

How deep do footings, decks and water lines need to be in Detroit?

House or garage footing Deck footing Water service line Fence post

House or garage footing in Detroit: dig at least 42 in (107 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Minimum depths in Detroit with a 42 in frost line
Project	Depth	Rule
House or garage footing	42 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	42 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	48 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	42 in	No code rule; common practice is below the frost line

Work out posts, concrete and footing sizes with the fence post depth calculator or the deck footing calculator.

How cold does it get in Detroit?

Average lows are at or below freezing from Dec to Mar. 125 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 19.4 °F.

NOAA 1991–2020 climate normals, Dearborn #2 station, 4.4 mi away, elevation 605 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	19.4	20.1	27.1	37.1	48.2	59.4	63.4	62.2	54.5	43.1	33.3	25.4
High	33	35.9	45.8	58.9	69.9	79.2	84.1	82	75.2	62.5	49.3	37.3

Detroit has fewer freezing nights than 54 of the 62 other Michigan places we track. The Michigan median is 143. Coldest: Marquette County; mildest: Allegan County.

How likely is the soil in Detroit to heave?

Low 27%Moderate 68%

USDA rates the sampled soil around Detroit as 27% low, 68% moderate, 5% high for frost action (main soils: Shebeon, Riverfront, Avoca).

USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.

How do you confirm the frost line before you dig in Detroit?

Call 811 (MISS DIG 811) at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Detroit building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 42 in unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

Detroit at a glance

Frost line depth: 42 in (Michigan rule)
County: Wayne County
Population (2023 est.): 633,218
Mean annual temperature: 50.3 °F
ZIP codes (34): 48126 · 48201 · 48202 · 48203 · 48204 · 48205 · 48206 · 48207 · 48208 · 48209 · 48210 · 48211 · 48212 · 48213 · 48214 · 48215 · 48216 · 48217 · 48219 · 48221 · 48223 · 48224 · 48225 · 48226 · 48227 · 48228 · 48233 · 48234 · 48235 · 48236 · 48238 · 48239 · 48240 · 48243