OR · statewide code figure
How deep do deck footings and fence posts have to go in Oregon? Below the frost line. Here's the number, and the winter behind it.
The requirement
12″
Footing bottoms in Oregon must reach 12 inches below grade — the frost line. Across Oregon it runs roughly 12″–24″ by county.
Reference: 2023 Oregon Residential Specialty Code, Section R403.1.4 (2023 edition). Counties amend their codes — confirm the exact figure with your local building department before you pour.
Depth pre-filled to the Oregon 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.
Western Oregon's mild, wet marine winters rarely freeze the ground more than a few inches, so the 12-inch code floor controls. Sustained cold at higher elevations east of and in the Cascades drives frost 18 to 24 inches down.
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.
The statewide ORSC ties depth to elevation: the 12-inch minimum below undisturbed grade governs below 2,500 feet, 18 inches applies from 2,500 to 4,000 feet, and 24 inches at or above 4,000 feet. Most population centers (Portland, Salem, Eugene, the coast) sit in the 12-inch zone.
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.
12 inches is the working number (statewide code figure). Across Oregon it runs roughly 12″–24″ 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 Oregon that means at least 24″. The post depth calculator checks both rules for you.
Below the frost line — 12″ 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.