Im working on a 2 story addition that is resting on 6x6 posts. Unfortunately due to timing I was unable to work out pouring a slab prior to our contractor begining our addition project and pouring the footings. So now I am left with a challenge I am over analyzing :).

Originally I wanted to put a 20'x10' slab or floating deck below the entire addition pictured, however because each footing is only 30" deep a single slab would require excavating below the footings on the left side of the photos.

As an alternative I'm thinking about a 2 tier slab or even a floating deck as pictured, but I am worried about undermining the posts either by surounding them in concrete or by digging too far down against the footings.

What would you do in this situation? The space will be unfinished and mostly used for storage. Text Text Text

  • 1
    Have you talked with your contractor to see what he suggests? It's his work you'll be disrupting, and he (should be) aware of your work and its potential impact on his...
    – FreeMan
    Oct 12 at 14:25

1 Answer 1


I'm not a construction worker but here is an idea: Use a metal shoring posts to secure the corner, then remove the shortest post. Excavate and replace it with a 6'11" post. Now leftmost and middle post are level.

Put a concrete tube around the rightmost post and pour an additional 1'1" of concrete so the top of the concrete levels with the top of the concrete of the middle post.

Now you can level and pour the slab. Assuming 5 inch slab, the whole area will have uniform height of 6`6".

Adding concrete around the post is not going to affect it negatively.

Shoring up the addition with a 1-2 jack posts will ensure you won't be undermining anything while you are replacing the one post.

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    "Adding concrete around the post is not going to affect it negatively." Pouring concrete around PT lumber will shorten its life. Moisture will stay in contact with the wood much more compared with lumber open to the air. Moisture=rot.
    – RetiredATC
    Sep 12 at 3:52
  • @RetiredATC Sounds like the posts have been there for a while, probably pretty dry already. I guess he can replace the rightmost post as well, but how much difference would it actually make?
    – ventsyv
    Sep 12 at 4:10
  • Posts were put in about 2 months ago... I'm also against pouring around posts although several landscapers have wanted to do it that way. How bad would it be to excavate about 12" of soil near the middle post so that atleast the right tier slab could be level with the right most footing top?
    – Squirrel
    Sep 12 at 12:39
  • @RetiredATC aren't the PT posts already in concrete?
    – Huesmann
    Sep 12 at 12:48
  • The posts are resting on top in a bracket
    – Squirrel
    Sep 12 at 13:12

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