Douglas County, CO Frost Line Depth: 36 in

Verified

36in

91 cm · 3 ft

Set in the building code Douglas County has adopted.

Source and how we checked

Document: douglasco.gov

Climate: 167 nights a year at or below 32 °F (NOAA 1991–2020, Castle Rock, 6 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

2 of 2nearby verified codes use the same depth
167nights a year at or below 32 °F
83%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Douglas County?

"{confirmed quote}". Footings, piers and other permanent supports must reach at least this depth (IRC R403.1.4.1).

Who sets the frost line depth in Douglas County?

Colorado leaves the frost line depth to each city or county, and Douglas County fills it in when it adopts the residential code. The value above comes from Douglas County’s own document on douglasco.gov. See how Colorado sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

House or garage footing in Douglas County: dig at least 36 in (91 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Minimum depths in Douglas County with a 36 in frost line
Project	Depth	Rule
House or garage footing	36 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	36 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	42 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	36 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 Douglas County?

Average lows are at or below freezing from Nov to Mar. 167 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 18 °F.

NOAA 1991–2020 climate normals, Castle Rock station, 6 mi away, elevation 6,185 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	18	19.9	26.5	32.5	41.6	50.5	56.4	54.7	46.6	34.6	25.7	18
High	45.6	46.7	53.8	59.1	68.4	80.2	85.7	83.6	76.7	64.8	53.9	45.7

Douglas County has fewer freezing nights than 8 of the 14 other Colorado places we track. The Colorado median is 176. Coldest: Eagle County; mildest: Littleton.

What frost line depth do towns near Douglas County use?

2 official codes near Douglas County are verified; each links to its document.

Official frost line depths near Douglas County
Place	Verified frost line	Distance
Arapahoe County	36 in	39 mi away
Broomfield	36 in	44 mi away

How likely is the soil in Douglas County to heave?

Moderate 83%

USDA rates the sampled soil around Douglas County as 10% none, 6% low, 83% moderate for frost action (main soils: Crowfoot, Peyton, Sandy wet alluvial land).

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 Douglas County?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Douglas County building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 36 in unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

Douglas County at a glance

Frost line depth: 36 in
Population (2023 est.): 383,906
Mean annual temperature: 49.6 °F
ZIP codes (18): 80016 · 80104 · 80106 · 80108 · 80109 · 80112 · 80116 · 80118 · 80120 · 80124 · 80125 · 80126 · 80129 · 80130 · 80131 · 80134 · 80135 · 80138