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I'm looking for some tips installing a jack post. For some background, I recently purchased a house. The previous owners covered a lot of issue and ended up with a terrible home inspector which didn't help. One of the issues we found after the purchase was a sagging joist below a load bearing column/short wall (Would have to remove drywall to figure out which one it is). Bad news, somebody previously removed the support below the load bearing area. It appears they tried to sister the joist at one point but it's enough. Good news, the original pier is still there so all I need is a post. I would prefer to install a beam spanning between the existing beams but plumbing and HVAC are in the way. Current plan is as follows:

  1. Install Simpson connections at each end of the double joist to help spread the load to the beams
  2. Install jack post on existing grout filled CMU pier
  3. Possibly Wedge piece of wood between jack post and the bottom of joist to engage adjacent joists
  4. Jack up the floor joist about an 1/8 of an inch each week until the floor is level

Questions are as follows. Did I miss any steps in my plan? Do I need to remove any finishes/baseboard before leveling the floor? Do I need to cut out the grout between bathroom tiles to prevent the tiles from cracking during the floor leveling? Is there a good method for locating the column from the crawlspace? I would like to make sure the column is bearing on the sagging joist directly.

I'm a structural engineer so I understand what is going on. However, most of my experience is design work for large commercial structures. I also respect the experience of contractors. Designing something and actually building it are two completely different animals. I appreciate all the help.

Also, I am fully aware our vapor barrier is trash and that our water pipes are not the best. I'm having the crawlspace encapsulated within the next year but want to fix the joist issues first.

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    To locate the column from the crawlspace, drill a hole through the floor at the base of the column/short-wall. Hang a flag through the hole to locate it from below. You mention a tile floor, where maybe there's some sort of transition material at column/short-wall, so such a transition would be a good invisible candidate.
    – popham
    Nov 6, 2023 at 4:00
  • Why the transverse beam instinct? As a hedge against the column/short-wall's vague location?
    – popham
    Nov 6, 2023 at 4:01
  • You are correct regarding the transverse beam. I would have no issue reinforcing just the sistered joist. However, that assumes the column/short wall is bearing directly on top of the joist which runs perpendicular to the wall above. I'll drill the hole and get an exact location like you said to verify. Might throw in some blocking between the joists running parallel to the wall once the joist has been leveled to help engage adjacent joists and spread the load if the bearing isn't exact. Nov 6, 2023 at 13:17
  • Is the load area right beside this tile? I suspect that the grout stiffens things up, so removing it could be counter productive. What size tiles are these? What material are they? Is the install new enough that there could be an uncoupling membrane? Is the deflection so noticeable that it requires fixing? Or can you just stiffen things up and leave it? Why the 1/8" per week? What is the total movement you're contemplating? Why not 1/8" per two months, say?
    – popham
    Nov 6, 2023 at 16:59
  • Under the Marble Institute of America's standard, natural stone tile requires an L/720 deflection limit versus the Tile Council of North America's L/360. Technically the L/360 is spec'ed by the latter for natural stone too, so there's a contradiction in spec's. Regardless, it's well established that natural stone is more delicate.
    – popham
    Nov 7, 2023 at 4:21

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