Frost depth in Colorado
Colorado has two code depths: 36 inches in 60 inches — and which one applies depends on the county you build in. Add 6 inches of bearing and that becomes a dig depth of 42" / 66". The numbers below are the code values an inspector measures, not climate averages — the local building department always has the final word.
| Area / zone | Frost depth | Dig depth | Set by |
|---|---|---|---|
| Front Range (Denver, Colorado Springs) | 36" | 42" | Denver amendments to IRC Table R301.2(1) |
| Mountain towns above 7,500 ft | 60" | 66" | Local amendment; engineer determination common |
Two rows, two numbers: the county you build in decides which one governs your permit. Never take the shallower value to a counter in a deeper zone.
Why Colorado's number looks the way it does
Colorado's Front Range runs a chinook-moderated 36 inches in Denver and Colorado Springs, but the mountain towns above 7,500 feet want 60 — and up there a geotechnical engineer's sign-off is common, because mountain soil freezes unevenly.
From frost depth to dig depth in Colorado
Footings bear on undisturbed soil below the frost line, so the hole goes 6 inches deeper than the code number. In Colorado that means:
| Code frost depth | Dig depth | Shortest Sonotube |
|---|---|---|
| 36" | 42" | 4 ft tube |
| 60" | 66" | 6 ft tube |
A 4-inch gravel base at the bottom of the hole is common practice for drainage, and if you use one, add it to the tube length rather than the dig depth — the footing still has to reach the full 36–60 inches below grade.
How much concrete a footing takes in Colorado
Bags of 80-lb mix per footing, for a solid pier with no post in the hole, at Colorado's code depth:
| Frost depth | 10" hole | 12" hole | 16" hole | 20" hole |
|---|---|---|---|---|
| 36" (42" dig) | 4 bags | 5 bags | 9 bags | 13 bags |
| 60" (66" dig) | 5 bags | 8 bags | 13 bags | 20 bags |
The bags calculator converts any total into 80, 60, 50 or 40-pound bags, and the concrete calculator handles slab and footing volumes.
Colorado frost depth FAQ
How deep is the frost line in Colorado?
Colorado has two code depths, and the county you build in decides which one an inspector measures: 36 inches in Front Range (Denver, Colorado Springs), and 60 inches in Mountain towns above 7,500 ft. These are code values, not the average depth the ground actually froze last winter.
How deep do footings have to go in Colorado?
Bearing sits below the frost depth, so dig to the code depth plus 6 inches: 36 inches of frost means a 42-inch dig, and 60 inches of frost means a 66-inch dig in Colorado. The extra 6 inches is the bearing layer that keeps the footing from sitting on frost-susceptible soil, and it is what Denver amendments to IRC Table R301.2(1) expects to see on a permit drawing.
How do I know which Colorado zone my county is in?
The citation in the table above names the authority that drew the lines — Denver amendments to IRC Table R301.2(1); Local amendment; engineer determination common. Your county or city publishes its own amendment to IRC Table R301.2(1) (or its own zone map), and that local document, not a state table, is what a permit reviewer checks. One call to the building department settles it before you rent an auger.
Plan a pour in Colorado
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Last updated: 2026-11-02