Correcting sagging floor with jack posts

Question

The center of my house has door alignment issues. Every few years they get out a bit more, so I plane them. It got me thinking of fixing it for good underneath the house. This house was built in 1946 and I've owned it since 2000. The degradation is slow, but has occurred over 24 years. This is in Los Angeles, so there's no frost issues. The ground is clay soil. It's on flat ground, not a hillside. It's a 1-story house with a crawlspace on dirt.

As you can see in the pics, the support beams in the center of the house start with a concrete pier, then a piece of 2" as the base, then a piece of 4"x4" supporting the joist. The problem seems to be the 2" base--they are compressing from the weight. One of them is compressed by about 1cm. It's harder to tell with the other because the compression is happening in the center of the wood, but you can tell it's compressing too because you can see the wood around it cracking and lifting.

I'm thinking about lifting in these spots just enough to undo the compression of those posts, to see if this corrects the door issue.

I've read about using a bottle jack to lift a tiny bit at at time, or turning a jack post 1/4 turn once a week, but would I:

a) Put the jack post on a concrete pad, or maybe a big square of 2"x6" (or even one of these composite footing pads?) sitting on the ground next to the existing post,

or

b) Lift with a bottle jack and put the jack post in place of the existing post?

The advantage to leaving the original posts in place is that if the lifting doesn't help, then I can just undo what I did and go back to this arrangement.

If I did put the jack post in place of the existing post, would I just set it on top of the concrete pier? It seems like a wood base is the wrong solution, because what's to stop it from compressing again like the existing one did?

Answer 1

The right long-term fix if you want ongoing adjustability is obviously to replace the existing post with the new jack. That's where the framing was configured to have support, and you don't want to change that.

Throw a big block down on the dirt and start jacking with a bottle jack (padded on top with a steel plate or something to spread load). Once the post is loose, knock it out and set the new jack post. Ease the bottle jack back down.

If your concern is being able to return the jacks if you don't need them, start by replacing the crushed block with new lumber. See if that helps. That might be all it takes. (It's rare to see crush like that--there must've been microbial decay over the years, or that's just a soft species of wood.)