Frost Line Depth in Oshkosh, WI: 48 in (Wisconsin rule)

State-set value

48in

122 cm · 4 ft

48 in (Wisconsin rule)

Set by the state: Wisconsin Uniform Dwelling Code SPS 321.16 (minimum; deeper where frost goes deeper).

Source and how we checked

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

Document: docs.legis.wisconsin.gov

Climate: 143 nights a year at or below 32 °F (NOAA 1991–2020, Oshkosh, 0.3 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

143nights a year at or below 32 °F
70%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Oshkosh?

Wisconsin sets the frost footing depth for Oshkosh at 48 in (122 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 Oshkosh?

Wisconsin writes this depth into its statewide residential code, so Oshkosh’s building department enforces the state’s number rather than setting its own. Winnebago County uses the same 48 in, so the depth does not change at the city limits. See how Wisconsin sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

House or garage footing in Oshkosh: dig at least 48 in (122 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Minimum depths in Oshkosh with a 48 in frost line
Project	Depth	Rule
House or garage footing	48 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	48 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	54 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	48 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 Oshkosh?

Average lows are at or below freezing from Nov to Mar. 143 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 10.2 °F.

NOAA 1991–2020 climate normals, Oshkosh station, 0.3 mi away, elevation 750 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	10.2	12.9	23.5	35.7	48	58.8	62.7	61	52.7	40.8	28.9	17.5
High	26.1	29.9	41.3	54.4	67.3	77.3	81.7	79.8	72.5	59	44.2	31.8

Oshkosh has fewer freezing nights than 34 of the 52 other Wisconsin places we track. The Wisconsin median is 150. Coldest: Marinette County; mildest: Racine.

How likely is the soil in Oshkosh to heave?

Moderate 70%High 30%

USDA rates the sampled soil around Oshkosh as 70% moderate, 30% high for frost action (main soils: Kewaunee, Udorthents, Manawa).

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 Oshkosh?

Call 811 (Diggers Hotline) at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Oshkosh building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 48 in unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

Oshkosh at a glance

Frost line depth: 48 in (Wisconsin rule)
County: Winnebago County
Population (2023 est.): 66,184
Mean annual temperature: 46.6 °F
ZIP codes (4): 54901 · 54902 · 54904 · 54985