Ohio does not set one statewide frost line. The Residential Code of Ohio leaves the number to each local building department. In Central Ohio, required footing depths usually run 32 to 36 inches: Franklin County lists 32 inches for conventional construction, and Dublin’s sample deck drawing calls for 36. Your building department’s number is the one that counts.
The frost line is how deep the ground freezes in a hard winter. Footings that stop above it can heave when the soil freezes and settle when it thaws, which racks decks, cracks foundations and pulls ledgers away from houses. Here is what the state code requires and what local offices publish.
Published Footing Depths in Central Ohio
Minimum depth below finished grade, as published by each office. Where we could not find an official figure, we say so. Call your building department before you dig.
| Jurisdiction | Minimum footing depth |
|---|---|
| Franklin County (unincorporated) | 32 inches for normal conventional construction |
| City of Dublin | 36 inches below grade on the city’s sample deck drawing |
| City of Columbus | Set in the city’s climatic and geographic design criteria. Confirm the current figure with Building and Zoning Services |
| Lancaster and Fairfield County | No official figure published online. Confirm with the City of Lancaster Building Department or your township |
What the Ohio Code Requires
From the Residential Code of Ohio, sections 301.2 and 403.1.4. Ohio numbers these without the “R” used in the national model code.
| Rule | What it says |
|---|---|
| Frost depth | Each jurisdiction fills in its own minimum footing depth in Table 301.2(1) |
| Minimum depth | Exterior footings at least 12 inches below undisturbed ground, and below the local frost line |
| Alternatives | A frost-protected shallow foundation, a design to ASCE 32, or footings on solid rock |
| Freestanding decks | Decks not supported by the house do not need footings below the frost line |
What It Means for Your Project
- Attached decks: footings go below the local frost line, because heave at the posts pulls on the ledger and the house
- Freestanding decks: Ohio’s code lets footings stay above the frost line, but the deck can still move, so stairs and walkways need room for it
- Additions: footings and foundation walls go below the frost line, or the design uses a frost-protected shallow foundation
- Pole barns: agricultural buildings can be exempt from the building code, but posts set too shallow still heave
- Fence posts are not covered by these rules, but setting them deeper helps for the same reason
Before You Dig
Call Ohio811 at least two working days before digging so buried utilities are marked. Most permits also call for a footing inspection before concrete is poured, so do not fill the holes until the inspector has seen them.
Questions, Answered
What is the frost line depth in Columbus, Ohio?
Franklin County lists 32 inches below grade for conventional construction in the unincorporated county. Inside Columbus, the city sets the figure in its climatic and geographic design criteria, so confirm with Building and Zoning Services at (614) 645-7433 before you dig.
Does Ohio have a statewide frost line?
No. Table 301.2(1) of the Residential Code of Ohio tells each jurisdiction to fill in its own minimum footing depth. That is why the number varies by city and county.
How deep do deck footings need to be in Ohio?
For a deck attached to the house, below your local frost line: 32 inches in unincorporated Franklin County and 36 inches on Dublin’s sample drawing. Ohio’s code lets decks that are not supported by the house skip the frost-depth requirement, though footings still have to carry the load.
What is a frost-protected shallow foundation?
A foundation that uses rigid insulation around the footing to keep the ground beneath it from freezing, so the footing can be shallower. Ohio’s code allows it as an alternative, with minimum depths of 12 to 14 inches depending on how cold the local climate gets. It has to be designed to the code’s insulation tables.
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See how we build them, with real project photos and reviews, on our Custom Decks & Porches page, or request a free written estimate.