Frost line depth in Colorado

Colorado has no statewide residential code, so the frost line is a jurisdiction question and the front range does not answer it uniformly. The 2022 Denver Building and Fire Code amends the model rule to 36 inches. Sixty miles south, the Pikes Peak Regional Building Department, which serves Colorado Springs and El Paso County, publishes 30 inches in its own regional code.

Six inches between two adjacent metros is not an error in either document. They are separate code-adopting authorities working from different local frost records, and it is a clean illustration of why a state-level frost number is a fiction in most of the country.

Colorado’s mountain jurisdictions publish considerably more, and nothing on this page should be read across to a building site above the front range. The state’s freeze record makes the point: its median station logs more nights below 20°F than Michigan or Massachusetts.

Across all 210 Colorado stations with published normals, the median first 32°F night falls around October 4 and the median station records 84 nights a year below 20°F, which is the coldest threshold NOAA counts and a decent proxy for a hard freeze rather than a light frost. The state’s spread runs from BOULDER 14 W, where the median first freeze is September 2, to PALISADE at October 26.

Colorado’s median station sees about 84 nights a year below 20°F and about 175 below freezing, numbers that sit closer to Wisconsin than to anywhere else in the mountain west. The spread is almost entirely vertical: Boulder 14 W, high in the foothills, reaches its median first freeze on 2 September, while Palisade on the western slope waits until 26 October. In Colorado, altitude is the variable that a state average erases.

Where these numbers come from

The Colorado frost figure was researched against the body that publishes it, and it’s recorded with a confidence note of “local only, varies” in our source ledger. Freeze dates are NOAA normals for stations in the state, picked by a fixed rule rather than by hand: first-order stations, spread west to east. The full method is on our methodology page.

• Freeze dates and cold-night counts: NOAA NCEI U.S. Climate Normals, 1991 to 2020, annual and seasonal by station. Retrieved 2026-09-09. Field definitions are in the by-variable readme.
• ZIP code locations: U.S. Census Bureau 2023 ZIP Code Tabulation Area gazetteer, matched to the nearest station by great-circle distance.
• 2022 Denver Building & Fire Code (official), frost protection amendment The Colorado frost depth figure and basis.
• Pikes Peak Regional Building Department, 2023 PPRBC, 2nd Printing The Colorado frost depth figure and basis.
• 2021 International Residential Code, Section P2603.5 (Freezing), ICC free code viewer The water service line burial rule.

The full method, including how we pick a station and what we do when there is not one close enough, is on our methodology page.