Frost Line Depth in Flint, 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

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

Document: codes.iccsafe.org

Climate: 148 nights a year at or below 32 °F (NOAA 1991–2020, Flint 7W, 4 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

148nights a year at or below 32 °F
54%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Flint?

Michigan sets the frost footing depth for Flint 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 Flint?

Michigan writes this depth into its statewide residential code, so Flint’s building department enforces the state’s number rather than setting its own. Genesee 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 Flint?

House or garage footing Deck footing Water service line Fence post

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

Minimum depths in Flint 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 Flint?

Average lows are at or below freezing from Nov to Mar. 148 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 16 °F.

NOAA 1991–2020 climate normals, Flint 7w station, 4 mi away, elevation 679 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	16	16.4	23.8	34.6	46.1	56.4	60.2	59.2	50.7	39.8	30.3	22
High	30.4	32.7	42.9	56.4	68.2	77.8	81.9	79.1	72.7	59.8	46.8	35.2

Flint has more freezing nights than 44 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 Flint to heave?

Moderate 54%High 46%

USDA rates the sampled soil around Flint as 54% moderate, 46% high for frost action (main soils: Crosier, Udorthents, Conover).

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 Flint?

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 Flint 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.

Flint at a glance

Frost line depth: 42 in (Michigan rule)
County: Genesee County
Population (2023 est.): 79,661
Mean annual temperature: 47.5 °F
ZIP codes (8): 48502 · 48503 · 48504 · 48505 · 48506 · 48507 · 48529 · 48532