Frost Line Depth in Naperville, Illinois
- Naperville’s adopted code
- Checked Oct 2026
- Sources
Verified
42in
107 cm · 3 ft 6 in
Set in the building code Naperville 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, 6.4 mi).
Checked Oct 2026. Report a correction
How deep is the frost line in Naperville?
Naperville'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 Naperville?
Illinois leaves the frost line depth to each city or county, and Naperville fills it in when it adopts the residential code. The value above comes from Naperville’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 Naperville?
House or garage footing in Naperville: 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 Naperville?
- J
- F
- M
- A
- M
- J
- J
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- N
- D
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, 6.4 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 |
Naperville 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 Naperville use?
5 official codes near Naperville are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Bolingbrook | 42 in | 5 mi away |
| Wheaton | 42 in | 8 mi away |
| Lombard | 42 in | 11 mi away |
| Hoffman Estates | 42 in | 22 mi away |
| Palatine | 42 in | 26 mi away |
How likely is the soil in Naperville to heave?
USDA rates the sampled soil around Naperville as 43% moderate, 57% high for frost action (main soils: Elliott, Ashkum, Orthents).
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 Naperville?
Naperville at a glance
- Frost line depth
- 42 in
- County
- DuPage County
- Population (2023 est.)
- 150,245
- Mean annual temperature
- 49.2 °F
- ZIP codes (9)
- 60440 · 60504 · 60532 · 60540 · 60555 · 60563 · 60564 · 60565 · 60585