Frost Line Depth in Great Falls, MT: Montana Codes Range 36

No official local value

No official frost line depth is published for Great Falls.

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: 143 nights a year at or below 32 °F (NOAA 1991–2020, Great Falls 16St, 1.4 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

36–42 inrange of verified Montana codes
143nights a year at or below 32 °F
72%of nearby soil rated “low” for frost action (USDA)

Does Great Falls have an official frost line depth?

No adopted frost line depth found for Great Falls in its official documents (checked Oct 2026). No verified code lies near Great Falls; the Montana codes we verified range from 36 to 42 in. Ask the building department for Great Falls’s own number before you dig.

What frost line depth does Great Falls use for footings under Table R301.2(1)?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Great Falls building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 42 in (the deepest verified state value) unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

How deep do footings, decks and water lines need to be in Great Falls?

Drawn with the deepest Montana official value (42 in). Confirm Great Falls’s own depth before you dig.

House or garage footing Deck footing Water service line Fence post

House or garage footing in Great Falls: dig at least 42 in (107 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Using the nearby official value of 42 in until Great Falls confirms its own
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 Great Falls?

Average lows are at or below freezing from Nov to Mar. 143 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 17.5 °F.

NOAA 1991–2020 climate normals, Great Falls 16st station, 1.4 mi away, elevation 3,505 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	17.5	18.7	25.2	33.2	41.9	49.6	55	53.4	44.7	35.9	26	19.8
High	36.8	38.6	48.2	58.3	67	75.4	85.8	83.9	72.6	59.1	45.3	36.7

Great Falls has fewer freezing nights than 7 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 Great Falls to heave?

Low 72%Moderate 28%

USDA rates the sampled soil around Great Falls as 72% low, 28% moderate for frost action (main soils: Kobar, Gerber, Yetull).

USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.

Great Falls at a glance

Frost line depth: No official local value
County: Cascade County
Population (2023 est.): 60,422
Mean annual temperature: 47 °F
ZIP codes (4): 59401 · 59404 · 59405 · 59414