Frost Line Depth in Navajo County, AZ: Flagstaff Requires 30 in

No official local value

No official frost line depth is published for Navajo County.

Nearby official codes require 30 in (1 verified code).

Source and how we checked

We searched this place’s own code and website and found no published frost line depth.

Climate: 172 nights a year at or below 32 °F (NOAA 1991–2020, Keams Canyon, 29.9 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

30 in1 verified code within 75 mi
172nights a year at or below 32 °F
78%of nearby soil rated “moderate” for frost action (USDA)

Does Navajo County have an official frost line depth?

No adopted frost line depth found for Navajo County in its official documents (checked Oct 2026). The nearest official values, from codes we verified, are 30 in. Use the deepest of them until the building department confirms Navajo County’s own number.

What frost line depth does Navajo County use for footings under Table R301.2(1)? Is it 30 in, like Flagstaff?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Navajo County building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 30 in (the deepest nearby 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 Navajo County?

Drawn with the deepest nearby official value (30 in). Confirm Navajo County’s own depth before you dig.

House or garage footing Deck footing Water service line Fence post

House or garage footing in Navajo County: dig at least 30 in (76 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Using the nearby official value of 30 in until Navajo County confirms its own
Project	Depth	Rule
House or garage footing	30 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	30 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	36 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	30 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 Navajo County?

Average lows are at or below freezing from Nov to Apr. 172 nights a year reach 32 °F or colder; Dec is coldest, with an average low of 16.7 °F.

NOAA 1991–2020 climate normals, Keams Canyon station, 29.9 mi away, elevation 6,205 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	17.5	21.9	26.5	32	39.2	46.8	56.7	54.9	47.2	34.6	24.5	16.7
High	44.9	49.3	57.9	65.5	74.5	85.6	89.4	85.9	79.1	68.1	55.9	43.7

Navajo County has more freezing nights than 34 of the 35 other Arizona places we track. The Arizona median is 12. Coldest: Flagstaff; mildest: Yuma.

What frost line depth do towns near Navajo County use?

One official code near Navajo County is verified.

Official frost line depths near Navajo County
Place	Verified frost line	Distance
Flagstaff	30 in	75 mi away

How likely is the soil in Navajo County to heave?

Low 22%Moderate 78%

USDA rates the sampled soil around Navajo County as 22% low, 78% moderate for frost action (main soils: Penistaja family, Betonnie, Moenkopie).

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

Navajo County at a glance

Frost line depth: No official local value
Population (2023 est.): 109,175
Mean annual temperature: 50.8 °F
ZIP codes (34): 84536 · 85901 · 85902 · 85911 · 85912 · 85923 · 85926 · 85928 · 85929 · 85930 · 85933 · 85934 · 85935 · 85937 · 85939 · 85941 · 85942 · 86025 · 86029 · 86030 · 86031 · 86032 · 86033 · 86034 · 86039 · 86042 · 86043 · 86044 · 86047 · 86054 · 86503 · 86505 · 86510 · 86520