Two builders, same week. One was framing a pole barn with five isolated pier footings. The other was building a 2,400 square foot house on a continuous perimeter footing. Both called us for footing excavation. The two digs looked nothing alike. Same tools, same crew, completely different approach.
A continuous footing is one connected concrete strip running under a wall. The load from the wall above spreads along the whole length of the footing. Most houses in the Greater Chattanooga area use continuous footings around the perimeter of the structure, with interior continuous footings under load-bearing walls.
A spread footing is an isolated pad of concrete under a single column or post. The load comes down one point — a steel column, a wood post, a pier — and the pad spreads it out into the soil. You see spread footings under porch posts, pole barn columns, deck piers, garage columns, and freestanding structural elements.
The excavation strategy for each is different in three big ways: layout, dimension, and access.
For a continuous perimeter footing on a typical home, the dig looks like this:
The work is fast when the layout is good and the soil cooperates. A 60 by 40 foot home perimeter can be opened up in a single day in average conditions. The challenge is keeping the bottom clean from one end to the other, especially when rain hits a 200 foot trench. We have walked a continuous footing trench in Ringgold at 5 a.m. with a shovel to pull out 2 inches of rainwater before the concrete trucks arrived. That happens.
A spread footing dig is the opposite. Instead of one long trench, you have a series of discrete pits. Each pit:
The challenge here is layout precision. With a continuous footing, the wall above sits on a long strip — a small layout error gets absorbed. With spread footings, the column or post comes down to a specific point on a specific pad. Miss the layout by 4 inches and the column is off-center on the footing, which can affect load transfer.
Continuous footings usually get dug with a mid-size or compact excavator running a clean-bottom bucket sized to the trench width. The machine walks the trench line, swings spoils to one side, and the dig moves fast.
Spread footings often get a smaller machine because the pits are tighter and there is more positioning between each one. On a pole barn with 10 piers, we may set up, dig, square the bottom, and reposition 10 times. Each pit takes longer than the same volume in a trench.
Most builds use both. A typical home in Ooltewah or East Ridge has:
We coordinate the sequence: continuous footings first when they share a wall with spread footings, isolated piers when they stand alone. More background on the foundation prep workflow is on the footings excavation pillar, and adjacent topics include building pads and concrete forming and pouring.
Two projects with similar concrete volumes can have very different excavation costs. Ten 3-foot-deep spread footings take longer to excavate per yard of concrete than 200 linear feet of continuous footing. Layout time, machine repositioning, and bottom cleaning all add up.
Continuous footings are standard around the perimeter and under load-bearing walls of most homes. Spread footings show up under columns, porch posts, and isolated point loads on the same building.
Only if the structure is designed for it. Some pole barns and post-frame buildings use spread footings under each post instead of a continuous perimeter footing. That is an engineering choice, not a substitution made at the dig.
Often yes. Because all the load comes down one point, spread footings are usually sized larger and dug deeper to spread the load into competent soil.
Yes. We typically dig continuous and spread footings on the same project in one sequence, and coordinate inspection timing for both before concrete arrives.
