Dallas County, IA Frost Line Depth: 42 in

Verified

42in

107 cm · 3 ft 6 in

Set in the building code Dallas County has adopted.

Source and how we checked

Document: dallascountyiowa.gov

Climate: 151 nights a year at or below 32 °F (NOAA 1991–2020, Perry, 11.2 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

2 of 2nearby verified codes use the same depth
151nights a year at or below 32 °F
81%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Dallas County?

Dallas County'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 Dallas County?

Iowa leaves the frost line depth to each city or county, and Dallas County fills it in when it adopts the residential code. The value above comes from Dallas County’s own document on dallascountyiowa.gov. See how Iowa sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

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

Minimum depths in Dallas County 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 Dallas County?

Average lows are at or below freezing from Nov to Mar. 151 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 10.2 °F.

NOAA 1991–2020 climate normals, Perry station, 11.2 mi away, elevation 950 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	10.2	14.1	25.8	36.7	49	59.8	63.5	60.8	51.5	39.1	26.8	16.5
High	29.5	34	47.5	61.3	71.9	81.9	85.4	83.3	77.1	64	47.8	35

Dallas County has more freezing nights than 22 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 Dallas County use?

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

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

How likely is the soil in Dallas County to heave?

Moderate 81%High 19%

USDA rates the sampled soil around Dallas County as 81% moderate, 19% high for frost action (main soils: Clarion, Spillville, Storden).

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 Dallas County?

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 Dallas County 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.

Dallas County at a glance

Frost line depth: 42 in
Population (2023 est.): 111,092
Mean annual temperature: 48.9 °F
ZIP codes (25): 50003 · 50038 · 50039 · 50061 · 50063 · 50066 · 50069 · 50070 · 50072 · 50109 · 50111 · 50128 · 50146 · 50156 · 50167 · 50220 · 50233 · 50235 · 50261 · 50263 · 50266 · 50276 · 50277 · 50323 · 50325