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I purchased a house built in 1960 and like other people have mentioned the terrible bounce, I got the same exact situation.

I'm thinking of installing blocking to strengthen the floor. The 7 joists are spaced 14½ However, since they're all buckled at the lower part of the joist, ranging from 14⅛ - 14⅞ I wanted to know if it's safe to wedge between 14½ blocks forcing them to move back that extra space. (see below picture)

I also so wanted to know if this load sharing would cause to much weight on other parts of floor beams.

enter image description here

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  • I don't think cross blocking is going to help much the bounce comes from the span the joists are across, sistering would help reduce the bounce.
    – Ed Beal
    Dec 17, 2018 at 23:22
  • What's your recommendation. Since I was thinking of doing the blocking or screwing in 16 gauged strapping underneath all joists
    – Joseph Wit
    Dec 18, 2018 at 1:10
  • If the loss of head space down below isn't an issue, you put a beam in the middle of the span sitting on two post jacks. Blocking keeps the house from racking. If the house is still standing it's probably sufficient. - That's good lumber in good repair with good blocking. Your electrician sucks though.
    – Mazura
    Feb 25, 2022 at 23:10

2 Answers 2

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I would sister several of the joists, then add solid blocking in each span. The blocking might not be critical, but the ceiling is now open so why not? Solid blocking does not need strapping across the bottom.
Look closely where the joists meet the load-bearing wall at each end. A 2x6 ledger might give extra assurance. Look at the rest of the floor structure for any splits, sags, movement, etc.

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  • How does the ledger look
    – Joseph Wit
    Dec 18, 2018 at 3:09
  • I'm sorry to make you crazy but can you explain your answer in layman's terms
    – Joseph Wit
    Dec 18, 2018 at 4:07
  • Also I wasn't thinking of putting strapping on the blocks I was saying that I would like to put strapping under the joists
    – Joseph Wit
    Dec 18, 2018 at 15:22
  • Add a second joist (sister joist) to each original joist. Use glue and nails/screws to effectively double the thickness of each joist. Run each new joist as long as possible, preferably to sit the first end on a load-bearing wall. Place each board with any curve (crown) facing up. You can force the second end up into place with a jack post, and nail it fully to the original. When all joists are done, secure a horizontal 2x6 (ledger) to support all the second ends. If you sister most of the joists, then blocking is optional and strapping is not needed.
    – John Canon
    Dec 19, 2018 at 4:55
  • What type of floor should I use and Where can I get a jack post
    – Joseph Wit
    Dec 19, 2018 at 5:00
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I have the same question regarding blocking twisted joists, and from what I've read, you would need to remove your floor sheathing (subfloor) to have an easier time straightening out the twisting. Since the lower part is wider than the top, you may want to block outside too to keep them from separating further. If you try putting a square 14.5" block in there you'll have gaps at the bottom. That may make nailing more difficult, and once the nails are in, it may be harder to close the gap. You could cut the block slanted to fit, but without finer measuring methods, good luck on cutting that perfectly. I would consider using a ticking stick. Still I'm not sure how I feel about blocking to conform to a twisted joist. Perhaps some blocking is better than nothing. Another idea is to ensure your subfloor and underlayment sheathing are nailed down well and that'll help your joists from twisting some. If the subfloor is removed, you could try pounding on either end of the joist where its nailed into the rim joists to straighten it out. You probably don't want to remove your subfloor if you don't have to though.

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