Frost Line Depth in Chicago, Illinois
- Chicago’s adopted code
- Checked Oct 2026
- Sources
Verified
42in
107 cm · 3 ft 6 in
Set in the building code Chicago has adopted.
Source and how we checked
Document: up.codes
Climate: 97 nights a year at or below 32 °F (NOAA 1991–2020, Chicago Northerly Is, 4.1 mi).
Checked Oct 2026. Report a correction
How deep is the frost line in Chicago?
Chicago'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 Chicago?
Illinois leaves the frost line depth to each city or county, and Chicago fills it in when it adopts the residential code. The value above comes from Chicago’s own document on up.codes. See how Illinois sets frost line depth.
How deep do footings, decks and water lines need to be in Chicago?
House or garage footing in Chicago: dig at least 42 in (107 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).
| 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 Chicago?
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Average lows are at or below freezing from Dec to Mar. 97 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 20.1 °F.
NOAA 1991–2020 climate normals, Chicago Northerly Is station, 4.1 mi away, elevation 583 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 20.1 | 23.1 | 30.9 | 40.4 | 50.1 | 60 | 67.3 | 67.4 | 60.2 | 47.7 | 36.4 | 25.2 |
| High | 31.9 | 35.7 | 44.9 | 55.2 | 65.7 | 75.8 | 81 | 80 | 73.2 | 60.9 | 48.5 | 36.6 |
Chicago has fewer freezing nights than 66 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 Chicago use?
5 official codes near Chicago are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Lombard | 42 in | 17 mi away |
| Glenview | 42 in | 19 mi away |
| Wheaton | 42 in | 22 mi away |
| Bolingbrook | 42 in | 24 mi away |
| Naperville | 42 in | 25 mi away |
How likely is the soil in Chicago to heave?
USDA rates the sampled soil around Chicago as 97% moderate, 3% high for frost action (main soils: Orthents, Ashkum, Aquents).
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 Chicago?
Chicago at a glance
- Frost line depth
- 42 in
- County
- Cook County
- Population (2023 est.)
- 2,664,452
- Mean annual temperature
- 50.8 °F
- ZIP codes (64)
- 60007 · 60018 · 60106 · 60131 · 60176 · 60601 · 60602 · 60603 · 60604 · 60605 · 60606 · 60607 · 60608 · 60609 · 60610 · 60611 · 60612 · 60613 · 60614 · 60615 · 60616 · 60617 · 60618 · 60619 · 60620 · 60621 · 60622 · 60623 · 60624 · 60625 · 60626 · 60628 · 60629 · 60630 · 60631 · 60632 · 60633 · 60634 · 60636 · 60637 · 60638 · 60639 · 60640 · 60641 · 60642 · 60643 · 60644 · 60645 · 60646 · 60647 · 60649 · 60651 · 60652 · 60653 · 60654 · 60655 · 60656 · 60657 · 60659 · 60660 · 60661 · 60707 · 60804 · 60827