WY · set by local jurisdictions
How deep do deck footings and fence posts have to go in Wyoming? Below the frost line. Here's the number, and the winter behind it.
The requirement
36″
Footing bottoms in Wyoming must reach 36 inches below grade — the frost line. Across Wyoming it runs roughly 36″–48″ by county.
Reference: City of Casper Engineering and Climatic Design Criteria (frost line 3 ft to top of footing); IRC adopted city by city, no mandatory statewide residential code (2024 edition). Counties amend their codes — confirm the exact figure with your local building department before you pour.
Depth pre-filled to the Wyoming frost line. The hole bottom has to reach it — a few inches deeper seats the base cleanly below.
| Bag size | Exact | Buy (with spare) |
|---|
The buy column adds a 10% spare margin and rounds up. Running out mid-pour is the one mistake you can't fix.
High elevation and long runs of subzero continental cold freeze the ground hard across the state; Casper's air freezing index is about 3,000 degree-days. That sustained cold pushes frost three to four feet down, deeper in the western mountains.
The depth tracks how much freezing a winter actually delivers. NOAA's Air Freezing Index keeps a running score of how far and how long air temperatures sit below freezing; deeper scores mean deeper frost, and building codes translate that climate record into the footing depth above. Water expands about 9% when it freezes — when that happens under a footing, the ground lifts it. That's frost heave, and it cracks foundations, tilts fence lines, and pops deck piers. Getting below the frost line puts your concrete where the ground never freezes.
Wyoming has no mandatory statewide residential code; Cheyenne and Casper both require 36 in., while high-elevation mountain jurisdictions go to 42-48 in. Some rural counties have no building department at all, so check locally before digging.
Treat this page as the starting number, not the permit. County and city amendments are where the real precision lives, and inspectors enforce the local figure — one phone call to the building department settles it.
36 inches is the working number (set by local jurisdictions). Across Wyoming it runs roughly 36″–48″ by county. Confirm the exact figure with your local building department — county amendments are common.
Bury one third of the above-grade height, never less than 24″, and never shallower than the frost line — in Wyoming that means at least 36″. The post depth calculator checks both rules for you.
Below the frost line — 36″ minimum, bearing on undisturbed soil beneath it. Size the diameter with the deck footing calculator, then figure bags with the depth pre-filled above.
Yes — 811 covers every state, and the locate is free. Call a few business days before any post hole or footing dig and crews mark the buried utilities.