Frost Line Depth in Rockford, Illinois
- Rockford’s adopted code
- Checked Oct 2026
- Sources
Verified
42in
107 cm · 3 ft 6 in
Set in the building code Rockford has adopted.
Source and how we checked
Document: rockfordil.gov
Climate: 136 nights a year at or below 32 °F (NOAA 1991–2020, Rockford Gtr Rockford Airport, 4.8 mi).
Checked Oct 2026. Report a correction
How deep is the frost line in Rockford?
Rockford'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 Rockford?
Illinois leaves the frost line depth to each city or county, and Rockford fills it in when it adopts the residential code. The value above comes from Rockford’s own document on rockfordil.gov. See how Illinois sets frost line depth.
How deep do footings, decks and water lines need to be in Rockford?
House or garage footing in Rockford: 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 Rockford?
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Average lows are at or below freezing from Nov to Mar. 136 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 14.5 °F.
NOAA 1991–2020 climate normals, Rockford Greater Rockford Airport station, 4.8 mi away, elevation 730 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 14.5 | 17.8 | 28.1 | 38.5 | 49.5 | 59.6 | 63.6 | 61.8 | 53.5 | 41.8 | 30.5 | 20.2 |
| High | 29.1 | 33.4 | 46.5 | 59.7 | 71.2 | 80.7 | 83.9 | 82 | 75.3 | 62.3 | 47.1 | 34.3 |
Rockford has more freezing nights than 53 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 Rockford use?
5 official codes near Rockford are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Hoffman Estates | 42 in | 49 mi away |
| Palatine | 42 in | 53 mi away |
| Wheaton | 42 in | 56 mi away |
| Naperville | 42 in | 58 mi away |
| Lombard | 42 in | 60 mi away |
How likely is the soil in Rockford to heave?
USDA rates the sampled soil around Rockford as 55% moderate, 45% high for frost action (main soils: Selma, Flagler, Griswold).
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 Rockford?
Rockford at a glance
- Frost line depth
- 42 in
- County
- Winnebago County
- Population (2023 est.)
- 146,120
- Mean annual temperature
- 49.4 °F
- ZIP codes (11)
- 61020 · 61088 · 61101 · 61102 · 61103 · 61104 · 61107 · 61108 · 61109 · 61111 · 61114