Anchorage, AK Frost Line Depth: 42 in (60 in for Cold Foundations)

Verified

42in

107 cm · 3 ft 6 in

42 in (60 in for Cold Foundations)

Set in the building code Anchorage has adopted.

Source and how we checked

Document: library.municode.com

Climate: 204 nights a year at or below 32 °F (NOAA 1991–2020, Eagle Rvr Nature Ctr, 4.2 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

204nights a year at or below 32 °F
66%of nearby soil rated “high” for frost action (USDA)

How deep is the frost line in Anchorage?

Anchorage's building authority sets the frost line depth at 42 in (107 cm) for a heated foundation and 60 in (152 cm) for an unheated (cold) one. Footings, piers and other permanent supports must reach at least this depth (IRC R403.1.4.1).

Who sets the frost line depth in Anchorage?

Alaska leaves the frost line depth to each city or county, and Anchorage fills it in when it adopts the residential code. The value above comes from Anchorage’s own document on library.municode.com. Anchorage Municipality uses the same 42 in, so the depth does not change at the city limits. See how Alaska sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

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

Minimum depths in Anchorage with a 42 in frost line
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 Anchorage?

Average lows are at or below freezing from Oct to Apr. 204 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 6.4 °F.

NOAA 1991–2020 climate normals, Eagle Rvr Nature Ctr station, 4.2 mi away, elevation 520 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	6.4	11.6	14.7	26.5	35.7	43.7	47.9	44.9	37.2	25.7	12.9	8.9
High	20.9	28	35.3	47.1	58	65.4	67.4	64.5	56	42.1	26.4	23.3

How likely is the soil in Anchorage to heave?

Moderate 34%High 66%

USDA rates the sampled soil around Anchorage as 0% low, 34% moderate, 66% high for frost action (main soils: E23-boreal subalpine scrub/meadow mosaic-silty till slopes, E23-boreal alpine scrub-gravelly colluvial slopes, E23-boreal forest-silty till slopes).

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 Anchorage?

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

Anchorage at a glance

Frost line depth: 42 in (60 in for Cold Foundations)
County: Anchorage Municipality
Population (2023 est.): 286,075
Mean annual temperature: 35.5 °F
ZIP codes (18): 99501 · 99502 · 99503 · 99504 · 99505 · 99506 · 99507 · 99508 · 99513 · 99515 · 99516 · 99517 · 99518 · 99530 · 99540 · 99567 · 99577 · 99587