Ankeny, IA Frost Line Depth: 42 in

Verified

42in

107 cm · 3 ft 6 in

Set in the building code Ankeny has adopted.

Source and how we checked

Document: ankenyiowa.gov

Climate: 150 nights a year at or below 32 °F (NOAA 1991–2020, Ankeny, 2.5 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

2 of 2nearby verified codes use the same depth
150nights a year at or below 32 °F
56%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Ankeny?

Ankeny's building authority sets the frost line depth 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 Ankeny?

Iowa leaves the frost line depth to each city or county, and Ankeny fills it in when it adopts the residential code. The value above comes from Ankeny’s own document on ankenyiowa.gov. Polk County uses the same 42 in, so the depth does not change at the city limits. See how Iowa sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

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

Minimum depths in Ankeny 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 Ankeny?

Average lows are at or below freezing from Nov to Mar. 150 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 11.7 °F.

NOAA 1991–2020 climate normals, Ankeny station, 2.5 mi away, elevation 975 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	11.7	16	27.4	38.1	50.3	60.8	64.7	61.7	52.9	40.5	28.9	18
High	29.5	34.2	47.4	61	71.9	81.8	85.7	83.7	77.1	63.6	47.8	34.7

Ankeny has more freezing nights than 17 of the 28 other Iowa places we track. The Iowa median is 144. Coldest: Cerro Gordo County; mildest: Davenport.

What frost line depth do towns near Ankeny use?

2 official codes near Ankeny are verified; each links to its document.

Official frost line depths near Ankeny
Place	Verified frost line	Distance
West Des Moines	42 in	16 mi away
Dallas County	42 in	23 mi away

How likely is the soil in Ankeny to heave?

Moderate 56%High 44%

USDA rates the sampled soil around Ankeny as 56% moderate, 44% high for frost action (main soils: Clarion, Canisteo, Nicollet).

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 Ankeny?

Call 811 (Iowa One Call) at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Ankeny 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.

Ankeny at a glance

Frost line depth: 42 in
County: Polk County
Population (2023 est.): 74,458
Mean annual temperature: 49.6 °F
ZIP codes (4): 50021 · 50023 · 50226 · 50317