Frost Line Depth in Lewis and Clark County, Montana
- Montana range from verified codes
- Checked Oct 2026
No official local value
No official frost line depth is published for Lewis and Clark County.
No verified code nearby; verified Montana codes range 36–42 in.
Source and how we checked
We searched this place’s own code and website and found no published frost line depth.
Climate: 169 nights a year at or below 32 °F (NOAA 1991–2020, Rogers Pass 9 Nne, 5.6 mi).
Checked Oct 2026. Report a correction
Does Lewis and Clark County have an official frost line depth?
No adopted frost line depth found for Lewis and Clark County in its official documents (checked Oct 2026). No verified code lies near Lewis and Clark County; the Montana codes we verified range from 36 to 42 in. Ask the building department for Lewis and Clark County’s own number before you dig.
What frost line depth does Lewis and Clark County use for footings under Table R301.2(1)?
How deep do footings, decks and water lines need to be in Lewis and Clark County?
Drawn with the deepest Montana official value (42 in). Confirm Lewis and Clark County’s own depth before you dig.
House or garage footing in Lewis and Clark 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 Lewis and Clark County?
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Average lows are at or below freezing from Nov to Apr. 169 nights a year reach 32 °F or colder; Feb is coldest, with an average low of 16.2 °F.
NOAA 1991–2020 climate normals, Rogers Pass 9 Nne station, 5.6 mi away, elevation 4,200 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 17.3 | 16.2 | 23 | 29.9 | 38.4 | 45.5 | 50.5 | 48.9 | 40.7 | 32.2 | 24.6 | 17.5 |
| High | 35.7 | 36.8 | 45.3 | 53.2 | 62.3 | 70.6 | 81.5 | 80.7 | 70.1 | 55.3 | 42.1 | 34.4 |
Lewis and Clark County has more freezing nights than 5 of the 7 other Montana places we track. The Montana median is 167. Coldest: Yellowstone County; mildest: Great Falls.
How likely is the soil in Lewis and Clark County to heave?
USDA rates the sampled soil around Lewis and Clark County as 100% moderate for frost action (main soils: Helmville, Mocmont, Tolex).
USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.
Lewis and Clark County at a glance
- Frost line depth
- No official local value
- Population (2023 est.)
- 75,011
- Mean annual temperature
- 43.9 °F
- ZIP codes (12)
- 59410 · 59421 · 59601 · 59602 · 59623 · 59625 · 59633 · 59635 · 59636 · 59639 · 59640 · 59648