Frost Line Depth in Colorado
36 inches in Denver, 30 on the southern Front Range, 48 and up in the mountains
Written by M., a general contractor in Richmond, VA · Last updated · Reviewed against the current Denver Building and Fire Code and county IRC adoptions
How Deep Is the Frost Line in Colorado?
Colorado has no statewide residential building code, so the frost line depth is set by each county or city. Denver, Aurora, Lakewood and Boulder use 36 inches; Colorado Springs (Pikes Peak Regional Building), Pueblo, Fort Collins and Greeley use 30 inches; Grand Junction uses 24 to 30; and mountain jurisdictions such as Summit, Eagle, Pitkin and Routt counties require 48 inches, with Leadville and other towns above 9,000 ft at 60 in. Elevation, not latitude, drives the number.
| State | Avg. Depth (in.) | Range (in.) | Major City Examples | Code basis |
|---|---|---|---|---|
| Colorado | 44 | 24 - 60 | Denver, Colorado Springs, Aurora | No statewide code; county and city Table R301.2(1) values (Denver 36 in) |
Returns the code depth for the nearest listed city and the regional note for that part of the state. A ZIP outside Colorado still resolves to its own state.
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All 50 states and the national map are on the frost line depth by ZIP code page. Footing width comes from the footing size chart and soil bearing capacity; roof loads from snow load by ZIP code.
What the Colorado Code Says
Colorado is a home-rule state with no statewide residential building code. Each county and municipality decides whether to adopt a code, which edition of the International Residential Code to use, and what to write into Table R301.2(1). The Colorado Division of Housing sets standards only for factory-built housing. As a result, the frost line depth changes at county lines, and sometimes at city limits, across the state. The one constant is the IRC R403.1.4 minimum of 12 in below undisturbed ground, which every adopting jurisdiction keeps.
On the northern Front Range, Denver amends the IRC to require 36 inches, and Aurora, Lakewood, Arvada, Westminster, Boulder and most of Jefferson, Adams and Arapahoe counties match it. South along Interstate 25, the Pikes Peak Regional Building Department (Colorado Springs and El Paso County) and Pueblo use 30 inches, as do Fort Collins, Loveland and Greeley to the north. On the Western Slope, Grand Junction and Mesa County use 24 to 30 in in the valley and more on the mesas. Once you climb into the mountains the values jump: Summit County (Breckenridge, Frisco), Eagle County (Vail), Pitkin County (Aspen), Routt County (Steamboat) and Gunnison County require 48 inches, and Leadville at 10,150 ft and other high towns require 60 in.
Most Colorado jurisdictions keep the IRC R403.1.4.1 exemption for freestanding accessory structures of 600 sq ft or less and allow frost-protected shallow foundations per R403.3, though mountain counties often require an engineer for FPSF because of their air freezing indices. Colorado's bigger foundation problem is expansive bentonite clay along the Front Range, which is why Denver-area homes sit on drilled piers or post-tensioned slabs regardless of frost depth; a soils report is required for new construction in most metro counties. Compare Colorado's range with the flatter Midwest on the national frost line table.
Frost Depth Zones in Colorado
With no statewide code, the values group by elevation and by which regional building department has jurisdiction.
| Zone or region | Footing depth | Where it applies |
|---|---|---|
| Denver metro (Denver, Aurora, Lakewood, Boulder, Arvada) | 36 in | Denver, Jefferson, Adams, Arapahoe, Boulder, Broomfield, Douglas counties |
| Southern and northern Front Range (Colorado Springs, Pueblo, Fort Collins, Greeley) | 30 in | El Paso (Pikes Peak RBD), Pueblo, Larimer, Weld counties |
| Western Slope valleys (Grand Junction, Montrose, Durango) | 24 to 36 in | Mesa 24 to 30 in; Montrose 30 in; La Plata / Durango 36 in |
| Mountain counties (Vail, Aspen, Breckenridge, Steamboat, Crested Butte) | 48 in | Eagle, Pitkin, Summit, Routt, Gunnison, Grand counties |
| High towns above 9,000 ft (Leadville, Fairplay, Alma) | 60 in | Lake and Park counties |
Colorado Frost Line Depth by City and County
Values below are the frost line depths each jurisdiction applies. Colorado cities within a county may adopt different editions and values; the county column names the department most likely to hold jurisdiction outside city limits.
| City | County | Required Footing Depth (in.) | Source |
|---|---|---|---|
| Denver | Denver | 36 | Denver Building and Fire Code amendments to IRC Table R301.2(1) |
| Colorado Springs | El Paso | 30 | Pikes Peak Regional Building Department, Table R301.2(1) |
| Aurora | Arapahoe / Adams | 36 | City of Aurora Building Division, Table R301.2(1) |
| Fort Collins | Larimer | 30 | City of Fort Collins Building Services, Table R301.2(1) |
| Lakewood | Jefferson | 36 | City of Lakewood / Jefferson County, Table R301.2(1) |
| Boulder | Boulder | 36 | City of Boulder Planning and Development Services, Table R301.2(1) |
| Pueblo | Pueblo | 30 | Pueblo Regional Building Department, Table R301.2(1) |
| Greeley | Weld | 30 | City of Greeley Building Inspection, Table R301.2(1) |
| Grand Junction | Mesa | 24 | Mesa County / City of Grand Junction, Table R301.2(1); 30 in on the mesas |
| Durango | La Plata | 36 | La Plata County Building Department, Table R301.2(1) |
| Breckenridge | Summit | 48 | Summit County Building Inspection, Table R301.2(1) |
| Vail | Eagle | 48 | Eagle County / Town of Vail, Table R301.2(1) |
| Aspen | Pitkin | 48 | Pitkin County / City of Aspen, Table R301.2(1) |
| Steamboat Springs | Routt | 48 | Routt County Regional Building Department, Table R301.2(1) |
| Leadville | Lake | 60 | Lake County Building Department, Table R301.2(1) |
Colorado has no statewide code and values change at county and city lines. Confirm with the jurisdiction that will inspect the footing; in the metro area that may be the city, not the county, and vice versa in unincorporated areas.
Decks, Fences and Water Lines in Colorado
- - Deck footings: Any deck attached to the house must bear below the frost line, so piers go to 30 to 48 in or deeper. Freestanding decks under the IRC R403.1.4.1 size limit may sit on pier blocks if the local inspector allows it. In the mountain counties, snow load (often 75 to 150 psf) sizes the pier more than frost depth does; see snow load by ZIP code. Size the pier with the deck footing size chart.
- - Fence posts: Code rarely requires frost depth for a fence that carries no structure, but posts set shallower than the frost line heave and lean within a few winters in Colorado. Use one third of the post height with a minimum of 24 in, and go to 30 to 48 in for gate and corner posts. Front Range fence posts fail from expansive clay as often as from frost; use gravel and a crowned collar. Bag counts are in the post hole bags guide.
- - Water lines: IRC P2603.5 puts exterior water service at least 6 in below the frost line and never shallower than 12 in, so the code floor here is your jurisdiction's frost depth plus 6 in (42 in in Denver, 54 in in the mountain counties). Many Colorado utilities require more; check the water department standard before trenching and call 811 first.
Neighboring states: Wyoming (36 to 42 in), Nebraska (42 in), Kansas (30 to 36 in), Oklahoma (18 in), New Mexico (18 to 36 in), Utah (30 in). When a project sits near a state line, the permit follows the jurisdiction where the footing is, not where the contractor is based.
Frequently Asked Questions
What is the frost line depth in Colorado?
It varies by jurisdiction because Colorado has no statewide code: 36 inches in Denver and most of the metro, 30 inches in Colorado Springs, Pueblo, Fort Collins and Greeley, 24 to 36 on the Western Slope, 48 inches in the mountain counties and 60 in towns above 9,000 ft.
What is the frost line in Denver?
36 inches to the bottom of the footing, per the Denver Building and Fire Code amendments to IRC Table R301.2(1). Aurora, Lakewood, Arvada, Westminster and Boulder use the same 36 in.
Why does Colorado Springs use 30 inches when Denver uses 36?
Different regional building departments reading different frost data. Pikes Peak Regional Building Department adopted 30 in for El Paso County; Denver adopted 36. Neither is wrong; each is the local jurisdiction's call under the IRC framework.
How deep do deck footings need to be in Colorado?
To the local frost depth: 36 in in Denver, 30 in in Colorado Springs, 48 in in Summit or Eagle County. In the mountains, ground snow loads of 75 to 150 psf usually make the footing larger than the frost depth makes it deeper. Denver-area decks on expansive clay often use drilled piers with void forms regardless of frost.
How deep should fence posts be in Colorado?
One third of the post height and at least 24 in for line posts; the local frost depth for gate and corner posts. On the Front Range, expansive bentonite clay heaves posts more than frost does, so 6 in of gravel below the post and a concrete collar sloped away from it matter as much as depth.
How deep are water lines buried in Colorado?
Frost depth plus 6 in is the code floor, but Colorado utilities go deeper: Denver Water requires 4.5 to 5 ft (54 to 60 in) of cover; Colorado Springs Utilities 5 ft; mountain districts 7 to 8 ft. Use the utility standard.
Sources
- No statewide code; county and city Table R301.2(1) values (Denver 36 in). Retrieved September 27, 2026.
- City and County of Denver, Community Planning and Development. Denver Building and Fire Code, amendments to the IRC. Retrieved September 27, 2026.
- Pikes Peak Regional Building Department. Adopted codes and design criteria for El Paso County. Retrieved September 27, 2026.
- International Code Council. 2024 International Residential Code, Table R301.2(1), R403.1.4 and R403.1.4.1. codes.iccsafe.org.
- National Weather Service, North Central River Forecast Center. Frost Depth Map. weather.gov.
City values are the frost line or minimum footing depths published or applied by each jurisdiction as of the retrieval date. Codes change on a three-year cycle and local amendments change between cycles; confirm with the building department before you submit a permit.