Hi Tony,

I am not an expert but I do know that you cannot simply put a post (column) onto an existing concrete floor. The 4" or so of concrete simply isn't thick enough for the load of a column. You will most likely need a 10" to 12" thick concrete footing, and the footing will likely need to be 30" or 36" square, depending on your local building code.

There is already a properly sized footer in place (which is a long story from the previous owner of the house).

Is this post going to support a beam or a joist? If there is a proper footing already there then is it possible a support was removed at some point in time? This would certainly explain the sagging floor. If the footing is there and you are supporting a standard size beam then the lally column will work fine.

I would use the existing footing. If it proves adequate, you are a big winner. If it proves inadequate, you are exactly where you are now plus you know exactly what is needed. You will not lose by trying it. I have welding equipment and I prefer to use the screw posts to get the house where I want it, then make a permanent, non-adjustable, post that just fits. I can get within 1/16 of an inch, close enough.

My husband and I talked to a few places about lally columns. We were going to buy the screwing one from home depot but my neighbor marv advised against that. After some research we decided to have them custom cut.

I luckily didn't have to install them :) Just did the foot work. But our house is still standing!

Here is a link that might be useful: Lally Column