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Just bought a new home with old - possibly original - hardwood, from '52. There's a relative bulge running down the middle of the house (or it could be sagging on either side) corresponding to the support beam in the basement. There are also some gaps between boards - both around the bulge but also in places where it's sagging, so that might just be humidity-related.

I've read - but don't know how reputable the source was - that a particularly heavy load (for instance, heavy appliances in like the fridge in the kitchen) can cause a joist to sag, and if the "extra" part of the joist that runs past the middle support (but does not run all the way to the far wall) extends too far past the support beam, it can counter-lever up and produce a bump.

Could that be happening here? If so, I was thinking I might trim the protruding portion of the joist so it can't counterlever (not reduce the length of the overall joist, just cut a small wedge off the top of the counterlever portion; see the pictures).

If that's not what's happening here, what can be done to fix it? I was thinking perhaps some more steel supports across joists beneath the kitchen, but they couldn't be very thick (maybe an inch or two at most) since we want to finish the basement and don't have much excess ceiling space.

Bulge (hard to see)

Basement support

Counter-lever

Counter-lever with cut

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    That's about what the floors in my house are like. It's about the same age and the joists aren't overlong like yours. 70+ year old joists sag. Commented Apr 25, 2023 at 18:55
  • Is chopping the top edge/wedge off (like the last picture) reasonable to avoid some of the counterlevering, if that's actually happening? The worst of the lump DOES appear to happen along the same joist as the fridge.
    – user112697
    Commented Apr 25, 2023 at 18:56
  • Most of that "bulge" is there because the middle of the joist is sagging. That's just geometry. So even if that levering is happening and you cut the protruding end of the joist, there'll still be a bulge. I'd either fix the entire joist (jack up then reinforce or replace) or leave it alone. Commented Apr 25, 2023 at 19:03
  • That's kind of what happens to old hardwood floors after a bunch of temperature and humidity cycles.
    – Huesmann
    Commented Apr 26, 2023 at 14:31
  • Joists from that era are usually undersized by current standards. Part of that is that current standards are for current lumber which has shrunk further from nominal size than what they had then, and which may be inferior quality, but part of that is also that Things Were Learned regarding long-term load-holding.
    – Ecnerwal
    Commented Apr 28, 2023 at 20:11

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