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My house was built in the 1980s and is your standard rectangular home, garage/basement on the bottom and living space above. I've been renovating the basement slowly and am trying to remove a few posts by adding a W6x25 steel I-Beam to the bottom of the houses central beam (over roughly a 16ft span). I hired a professional to confirm the plan and ensure what I do was structurally sound and safe, but I've hit a snag.

While building an auxiliary wall for support before installing the beam I realized that a section of my houses central beam has sagged just over an inch. It has a wooden support post (4x6) that I'm assuming the previous owner tossed in as it's shorter than all of the other steel posts present.

I'm curious if there is a safe way to raise that section the required distance so that I can finish the support wall and eventually add the underlaying steel beam, or am I out of luck?

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    Possible, but is not fast. A little bit every few days, so a few weeks. If the beam is bent, then will need to raise the floor instead of the beam(beam probably toast if bent).
    – crip659
    Feb 4 at 12:36
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    Is the steel beam supposed to replace the wood one, or reinforce it (and if so, from below or from the side)? A pic/sketch would help us out here.
    – Huesmann
    Feb 4 at 13:46
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    Raising it up is the simple-ish part, with a temporary post and hydraulic jack. The bigger problem is what happens to everything above it: that much adjustment is likely to break plaster/sheetrock, trim, etc. if work was done after the settling occurred. Doors above may also end up out of alignment and stick, or not close at all.
    – nobody
    Feb 4 at 14:07
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    You've checked it with a self leveling laser or an optical instrument? It's odd to discover something like that from below instead of from walking on it. You're sure that you're not measuring from an out-of-level basement slab?
    – popham
    Feb 4 at 17:54
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    If the steel column layout seems to imply that a column should be at the post's location, then that could mean that there's a scar in the slab below your 4×6 where a failed steel column once stood. If such a scar exists, then diagnosing the steel column's failure could be worthwhile.
    – popham
    Feb 4 at 17:57

2 Answers 2

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The general trick with jacking a house that has sagged over 40 (or 140) years is that you should not un-sag it in a matter of days, or even weeks, unless the sag is very minor.

The jack has no problem moving it fast, but the house will have problems if you do.

Something on the order of 1/8" (3mm) and then wait 2-4 weeks is less likely to cause problems as the house adjusts, though you may still get some cracking of drywall. If things have been patched or trimmed as the beam sagged, those spots may well be more prone to gap or crack as it is raised.

I have been involved in this process in the house I grew up in, the barn of the house I grew up in, and my sibling's house. The brains behind the operations was a civil engineer who I'm related to. You could certainly ask for advice from the engineer who planned your new beam in the first place.

Hydraulic jacks are good for moving, screw jacks are better for holding. Lally columns with screw jacks are commonly available. You may want to install the steel beam under the wood one and then jack the pair of them into place (very slowly) before fixing the steel beam permanently.

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    The cheapest pattern is probably a hydraulic jack, the current post plus a jacking post, and a pair of wedges. Buying the screw jack rather than renting over the long timeframe is probably cheaper, although you could probably buy the screw jack from a corporate hardware store, take good care of it, and return it months later.
    – popham
    Feb 4 at 18:09
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Sounds like you measured once, built a wall, and stood it up to discover that it doesn't fit. Check the levelness of the slab below this wall. Run a stringline along the length of the beam or use a self leveling laser and a measuring tape (you'll want the stringline anyway as you implement Ecnerwal's solution). The odds are good that floor lumpiness instead of ceiling sag is your problem.

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