Lombard, IL Frost Line Depth: 42 in

Verified

42in

107 cm · 3 ft 6 in

Set in the building code Lombard has adopted.

Source and how we checked

Document: library.municode.com

Climate: 144 nights a year at or below 32 °F (NOAA 1991–2020, Lisle-Morton Arboretum, 5.1 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

5 of 5nearby verified codes use the same depth
144nights a year at or below 32 °F
67%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Lombard?

Lombard'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 Lombard?

Illinois leaves the frost line depth to each city or county, and Lombard fills it in when it adopts the residential code. The value above comes from Lombard’s own document on library.municode.com. See how Illinois sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

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

Minimum depths in Lombard 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 Lombard?

Average lows are at or below freezing from Nov to Mar. 144 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 14.7 °F.

NOAA 1991–2020 climate normals, Lisle-Morton Arboretum station, 5.1 mi away, elevation 680 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	14.7	17.7	26.1	36.1	47.4	57.9	61.8	60.2	52.3	40.4	29.9	20.6
High	31.5	35.2	47.2	59.2	70.6	80.7	84.4	82.7	76	62.6	48.4	36.6

Lombard has more freezing nights than 62 of the 71 other Illinois places we track. The Illinois median is 127. Coldest: Hoffman Estates; mildest: Madison County.

What frost line depth do towns near Lombard use?

5 official codes near Lombard are verified; each links to its document.

Official frost line depths near Lombard
Place	Verified frost line	Distance
Wheaton	42 in	5 mi away
Naperville	42 in	11 mi away
Bolingbrook	42 in	14 mi away
Hoffman Estates	42 in	15 mi away
Palatine	42 in	17 mi away

How likely is the soil in Lombard to heave?

Moderate 67%High 33%

USDA rates the sampled soil around Lombard as 67% moderate, 33% high for frost action (main soils: Orthents, Markham, Ashkum).

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 Lombard?

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

Lombard at a glance

Frost line depth: 42 in
County: DuPage County
Population (2023 est.): 43,779
Mean annual temperature: 49.2 °F
ZIP codes (3): 60137 · 60148 · 60523