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We’re installing hardwood flooring in our second floor master bedroom. House was built in 1993. When we pulled off the carpet we realized the floor dips in the middle. The room is 18 ft (north-south) x 14 ft (east -west) and the dip starts about 2 feet from the north and south walls. There’s a 4 ft (north-south) x 8 ft (east-west) section in the middle where the dip is about one inch.

Looking for advice on how to correct this. my first thought was self-leveler like Henry 555, but that seems like a lot and I’m a little concerned about asking the floor to support that much additional weight. I also thought about putting a 3/4” x 4 x 8 sheet of plywood or MDF in the lowest area and using self-leveler elsewhere. And finally I thought about pulling up the subfloor and shimming the joists to bring at least the worst parts of the floor level.

I’m unsure what the best option is and interested in opinions. Thanks in advance for your help!

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    That much distortion seems extreme for such a young building, What's beneath the middle of that room?
    – Jasen
    Oct 25, 2021 at 2:00
  • The first floor on that side is an open kitchen/dining/living room that in total is about 13 x 28. The dipping area is roughly in the middle of that. I haven’t noticed any ceiling sagging in the area under the bedroom. Oct 25, 2021 at 3:19
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    Based on what you’re saying, it sounds like you might have a structural problem, like a span that is supported by some undersized beam— or something that has caused an existing beam to fail like water or pest damage. What furniture has been in the center of the room, traditionally? Are you the sole and original owner of the house? Any unpermitted renovations? Finally, who built the house? Is it in a single-builder subdivision? Oct 25, 2021 at 4:30
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    How many levels is the house? I have a 95 build, 3 floors with the top floor has a dip in the middle where you expect it. My build has concrete foundation wall on the exterior and the middle is posts / joist / beams. The lumber was installed wet and shrunk. 1/2" per level probably shouldn't be surprising. 2x10s wet are 9.5 when dry can go down to 9" add a little shrinkage for the subfloor. Nothing wrong with my ceilings by eye. Oct 25, 2021 at 6:11
  • @RibaldEddie, we just bought the house so don’t have the history. The previous owners gave us their history and they didn’t do make any structural changes to the interior. I imagine the only major furniture they had in the room was a bed and a dresser. Oct 25, 2021 at 12:33

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You have a few options. You've noted most of them. An additional one would be jacking up the interior middle of your floor assembly from the lower floor and replacing the post or shimming the wall that is holding up the middle of that floor. That option depends on how many levels you have and your tolerance for fixing up drywall that cracks along the way. Are any of the door jambs on the top floor visually asymmetric? Do you have tile floor finishings that you'd be distraught having crack. If you have 3 levels possibly this is 1/2" per floor but then the work is doubled.

If I had to do that job, I'd laminate with the 1" ply for the 4x8 section and expand outward with 3/4" pieces, 1/2" pieces and when most of the volume of the deflection was filled I'd use the primer/SLC or pay someone to do the primer / SLC. After doing the SLC work, I am happy to pay someone now.

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  • thanks for sharing your thoughts. I’m going to check the ceiling below to see if there’s any bowing or sagging - there doesn’t seem to be any but worth double checking. If there isn’t any, I’m guessing the issue isn’t structural and the cause is more along the lines of your previous comment - general joist shrinkage and compression. Thanks for your help! Oct 25, 2021 at 12:53
  • I did find a corresponding bulge on the ceiling below. I take it this this makes a structural cause more likely? Oct 25, 2021 at 15:06
  • What is the size of the bulge? If you have a bulge probably best to open up that area of drywall so you can inspect and see what is going on. Oct 25, 2021 at 15:55
  • I took up the subfloor over the dip/bulge and don’t see anything unusual - there’s actually a double joist there. It doesn’t seem to move under weight or impact. I’m thinking maybe they put in the joists wrong side up and/or someone had something heavy in the room like a waterbed. But it doesn’t seem to be a structural problem from what I can tell. Anything else you think I should check? Oct 25, 2021 at 19:27
  • @DaveFriederichs if you put a long level or straightedge along the joists, is it clear that their tops aren’t level? What’s the size of the joists? 2x10? Oct 25, 2021 at 21:25

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