Frost, clay, and concrete: why footing depth decides whether your deck stays level.

The ground under your deck is not still

When soil freezes, the water in it doesn't just harden in place — it migrates. Freezing soil pulls moisture toward the frost front and stacks it into layers of ice called ice lenses, and those lenses expand with enormous force. Enough force to lift a pickup truck; certainly enough to lift a deck footing. Then spring comes, the lenses melt, and the footing settles — but never quite back to where it started.

A footing poured above the frost line rides this elevator every winter. The symptoms arrive gradually: a gate that stops latching, a railing that leans, stair risers that drift out of code, decking that puddles where it used to drain. By year five the deck isn't dangerous yet — it's just visibly, permanently crooked, and there is no fix short of re-supporting it.

The solution is old and unglamorous: bear the footing on soil that never freezes. In central Kentucky that means excavating below the local frost depth — around two feet in our counties, and we verify the required depth with the local building office on every permit, because the county's number is the one the inspector holds us to.

Depth is half the answer. Bearing is the other half.

A footing has two jobs: get below frost, and spread the load. Every post on your deck concentrates thousands of pounds — the structure, the furniture, the hot tub, the twenty people at graduation — onto a circle of concrete the size of a dinner plate or a trash can lid. Whether the soil under that circle holds depends on two things: how big the circle is, and what the soil is.

Our region's clay soils are decent bearers when undisturbed, but they are not uniform, and fill dirt — common around newer homes, where the builder backfilled the foundation — can carry a fraction of the load of native ground. This is why footing size isn't a habit; it's arithmetic. You take the tributary load each post carries (its share of the deck's design load), divide by the soil's presumptive bearing capacity, and that gives you the bearing area — the footing diameter. A heavier deck, a bigger span, or softer soil means a wider footing. Full stop.

Two details matter as much as the math. Footings must bear on undisturbed soil — concrete poured onto loose backfill settles no matter how deep it is. And the bottom of the hole must be clean and dry when the pour happens; a footing poured onto a slurry of mud has a bearing surface nobody calculated.

Why we photograph our holes

Footings are the classic place to cheat because they're invisible by lunchtime. Our answer is simple: we treat the inspection as a feature. Holes are dug to the county-verified frost depth, sized to the load calculation on your proposal, inspected open by the county before concrete goes in, and photographed — depth tape in frame — for your project file. You'll never see your footings again, so we make sure you've seen them once.