We have a small cabin that we would like to extend 10 feet in the back. It has a crawl space. The architect and engineers have designed a new floor plan for the house that involves putting new footings (Piers) under the back wall, in addition to several other footings to support the extension. It's a pretty big job for such a small cabin. It involves putting a new roof on the entire structure too.

I was wondering, just out of curiosity, how is it possible to put a new deep footing under an existing wall? Digging a hole for a pier seems pretty straightforward with an auger in an open space. But how would it be done underneath the exterior beam of the house? Is it even possible, or would the beam need to be removed in the process? Or is there some way to drill sideways to accommodate the pier?

I really wish the architect could have done it another way. I won't be doing this myself, of course, but I was just wondering what we are asking the builders to do.

  • How deep are the piers to go below existing grade? What size are the piers? Is a “spread” footing to be installed under the pier? Are the piers to be cast-in-place or pre-made?
    – Lee Sam
    Jul 27, 2018 at 21:36

1 Answer 1


You haven't said what the foundation (referred to as a "beam") is built of. A poured foundation can span gaps of several feet temporarily. A block foundation may be supported by adequately reinforced footings. A temporary beam carrying some of the load on the floor joists could also be employed.

As to how... a shovel. Despite our many evolutionary regressions due to over- abundant modern conveniences, we're still able to grasp and manipulate simple tools fairly effectively.

It's also possible that a backhoe could cut in from outside the foundation and bore underneath.

  • 1
    Standard foundation work is piers under exterior beams, and the beam is not removed. I have seen offset drill augers being used. Jul 27, 2018 at 21:18
  • @isherwood I didn't actually think of using a backhoe. Yeah, I don't know, beam, exterior joist, whatever the word is. The house is on piers. No blocks or concrete floor. Thank you.
    – Dave
    Jul 27, 2018 at 21:39
  • Oh, then I completely misunderstood. Feel free to leave the question open for awhile to get more answers.
    – isherwood
    Jul 27, 2018 at 22:29

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