Frost Line Depth in Johnson County, Iowa
- 2 verified codes nearby
- Checked Oct 2026
No official local value
No official frost line depth is published for Johnson County.
Nearby official codes require 42 in (2 verified codes).
Source and how we checked
We searched this place’s own code and website and found no published frost line depth.
Climate: 135 nights a year at or below 32 °F (NOAA 1991–2020, Iowa City Municipal Airport, 3.6 mi).
Checked Oct 2026. Report a correction
Does Johnson County have an official frost line depth?
No adopted frost line depth found for Johnson County in its official documents (checked Oct 2026). The nearest official values, from codes we verified, are 42 in. Use the deepest of them until the building department confirms Johnson County’s own number.
What frost line depth does Johnson County use for footings under Table R301.2(1)? Is it 42 in, like Cedar Rapids?
How deep do footings, decks and water lines need to be in Johnson County?
Drawn with the deepest nearby official value (42 in). Confirm Johnson County’s own depth before you dig.
House or garage footing in Johnson County: 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 Johnson County?
- J
- F
- M
- A
- M
- J
- J
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- S
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- N
- D
Average lows are at or below freezing from Nov to Mar. 135 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 14.6 °F.
NOAA 1991–2020 climate normals, Iowa City Municipal Airport station, 3.6 mi away, elevation 650 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 14.6 | 18.5 | 29.5 | 40.1 | 51.7 | 62.1 | 65.8 | 63.3 | 54.2 | 42.1 | 30.4 | 20.1 |
| High | 30.9 | 35.5 | 49.5 | 62.6 | 73.4 | 82.6 | 85.8 | 83.8 | 77.5 | 64.1 | 49.2 | 36.3 |
Johnson County has fewer freezing nights than 18 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 Johnson County use?
2 official codes near Johnson County are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Cedar Rapids | 42 in | 21 mi away |
| Linn County | 42 in | 28 mi away |
How likely is the soil in Johnson County to heave?
USDA rates the sampled soil around Johnson County as 18% low, 7% moderate, 76% high for frost action (main soils: Fayette, Colo, Chelsea).
USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.
Johnson County at a glance
- Frost line depth
- No official local value
- Population (2023 est.)
- 157,528
- Mean annual temperature
- 51 °F
- ZIP codes (24)
- 52203 · 52227 · 52228 · 52235 · 52240 · 52241 · 52242 · 52245 · 52246 · 52247 · 52253 · 52317 · 52322 · 52325 · 52327 · 52333 · 52338 · 52340 · 52356 · 52358 · 52404 · 52755 · 52766 · 52776