Concrete Pier Footings: Drilled, Bored, Belled, and Deck Piers Explained

Not every load on a foundation plan sits on a continuous footing. Where the soil near the surface can’t be trusted, where frost would heave a shallow footing, or where a structure only touches the ground at a few points — a deck, a porch, a fence, a pier-and-beam house — the plan calls for piers instead. A pier footing is a vertical concrete column that carries a point load straight down to firm ground.

Piers get confused with pads, with piles, and with each other. This guide separates the pier types you’ll actually meet on residential and light-commercial plans — drilled, bored, belled, and Sonotube deck piers — explains how deep and how wide they go, and shows why a pier is always a count on the takeoff, never a length.

What is a concrete pier footing?

A concrete pier footing is a vertical concrete element that transfers a concentrated load from a post, column, or beam down to soil that can bear it — typically below the frost line. It differs from a strip footing in a single decisive way: a strip footing spreads a line load along a wall, while a pier carries a point load down at one spot.

Most piers resolve their load two ways at once: end bearing on the soil under the base and skin friction along the sides of the shaft. When the base is widened — either as a separate spread footing or as a drilled bell — the pier can carry more load or bear on weaker soil. That is the whole design lever: a pier is a column, and the base under it is what actually sits on the dirt.

Because a pier is a discrete support, it lives on the takeoff as a counted unit, alongside pads, not folded into the linear feet of continuous footing.

Bored, drilled, and belled piers

On engineered residential and light-commercial jobs, the pier is usually drilled rather than hand-dug. An auger bores a round hole to depth, and the hole is filled with concrete — often around a reinforcing cage. These go by several names that describe the same family of deep, cast-in-place columns.

A bored pier carries load through end bearing plus side friction. A belled pier — also written belled caisson — is the same shaft with a flared base drilled wider than the shaft to increase bearing area, so the pier bears a heavier load without a separate spread footing. The distinction between a drilled pier and a pile is mostly method and scale: piers are typically drilled and cast in place, piles are usually driven or drilled to greater depth and tie into a pile cap. For a footing sub’s takeoff, all of these are counted units — the number of piers, not a length — even though the drilling contractor may price them by the linear foot of shaft.

Sonotube deck and porch piers

The pier you’ll meet most often on residential work is the Sonotube pier under a deck, porch, or covered entry. A Sonotube is a waxed cardboard forming tube; the pier is the concrete inside it. On its own a Sonotube is only a form and has no structural value — the load is carried by the concrete column and the footing base beneath it.

That base matters. A proper exterior deck pier is really a pier plus a footing: the tube sits on a widened concrete pad or a manufactured spread base at the bottom of the hole, below the frost line, and the tube forms the column up to grade. Skip the base on soft soil and the pier punches down.

Deck and porch piers must reach frost depth. Under the International Residential Code, deck footings are required to bear at or below the frost line for the jurisdiction, the same rule that governs any exterior footing. Common residential deck piers run a 10 to 12 inch diameter tube on a wider footing base, but the diameter and base size come from the post load and the local code, not from habit.

How deep and how wide

Two dimensions define a pier: how deep it goes and how wide its base is. They answer two different questions.

Depth answers frost. A pier footing has to bear below the local frost line so it can’t be lifted by heaving soil. Frost depth is set by the local building department and varies enormously by region:

Frost depths above are illustrative ranges only — the frost line is set locally and you must confirm the figure with your building department; adjacent towns can differ. Width answers bearing: the base has to spread the point load over enough soil to carry it. When the soil is weak or the load is high, the base is widened — as a spread footing under the pier or as a drilled bell — rather than making the shaft deeper. The plan’s pier schedule or the engineer’s detail gives the shaft diameter and base size for each pier; read it and don’t assume a single size across the job.

Pier-and-beam foundations

Where piers carry a whole house rather than a deck, you’re looking at a pier-and-beam foundation. Instead of a continuous perimeter footing and slab, the structure sits on a grid of concrete piers; beams span between them, and the floor framing sits on the beams over a crawl space.

Pier-and-beam is common in expansive-clay regions and in older housing because the piers reach past the moving surface soil to stable ground, isolating the structure from seasonal heave and shrinkage, and the crawl space keeps plumbing and framing reachable. On a takeoff, a pier-and-beam plan is a pier count — every pier location on the grid — plus any grade beams measured as linear footing. The two live on separate invoice lines because one is billed per pier and the other per foot.

The takeoff rule: piers are counted, never measured in feet

The rule that keeps a footing takeoff honest applies to piers exactly as it does to pads: a pier is a count, not a length. Each pier is one point support, with a roughly constant amount of drilling or digging, forming, reinforcing, and concrete. Footing subs bill piers per pier — a flat rate each — because the effort per pier barely changes with the plan.

Two habits keep piers clean on the takeoff:

• Count every pier location off the pier schedule and the plan grid, and note the diameter and depth call-out. If posts are shown with no pier drawn, flag it — don’t invent a count.
• Keep piers on their own invoice line, separate from the linear-foot total for continuous footings, priced at your flat per-pier rate.

Piers and interior support pads are both counted units, but they are not the same element — a pad is a shallow isolated footing under an interior post, while a pier is a deep column reaching below frost. Get the two on the right lines and the invoice reconciles against the wall company’s own counts. To see how the pier count, the pad count, and the linear-foot total sit together on one invoice, walk through the footing takeoff guide; to total a run of piers at your flat rate quickly, the free footing calculators at footingcalc.com handle the arithmetic. An automated pass through FootingTakeoff counts piers and pads as units and keeps them off the linear-foot line automatically — which is exactly where they belong.