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Thread: Cross bracing floor joists

  1. #1
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    Cross bracing floor joists

    Floor joists are normally connected with X bracing or solid blocking. The value of this bracing is often unappreciated and it is done poorly. My braces are of low quality wood that has been nailed without care. Many are split by the nails and most of the nails are awry. Then the trades came thru and removed some to make their installation easier. This leads to squeaky floors which I want to fix. House is 35 years old so no recourse to the builder who is long dead.

    My question is how to do it. Nailing in new braces is not possible with the subfloor in place and with the spaces filled with wiring, piping, ducts etc it is not practical. Solid blocking might be possible but the obstructions are still a problem. Adding supporting walls or beams with posts is not a good option as it would cut up the basement. Any suggestions?

  2. #2
    Squeaking floors are generally caused by poorly secured sub flooring. There are methods for addressing that problem from above and below. Bridging of joists aids in making the floors less bouncy. I added solid blocking to our floor from the basement. I measured each joist space and cut an appropriate 2 x 10 to fit snugly. I installed it with long construction grade screws. I staggered the blocks back and forth along the length of the run so I could put screws in from each end. There isn't much you can do about duct runs or plumbing.
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  3. #3
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    We fixed our squeaky floors by screwing down the subfloor which had originally been nailed. Even with perfect cross bracing there will still be movement which could cause squeaks.

  4. #4
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    Yes, squeaky floors are the result of the sub floor inadequately attached to the floor joists. If you can't add screws or nails from above, one option would be to squirt/force some adhesive between the subvfloor and floor joist from below. Not easy, most just sticks to the juncture, but still may do the job. Also, have someone walk on the floor above as you listen and watch from below for squeaks and movement. If you can spot the location, try doing the adhesive thing. Another option is, once you have identified the squeaky joists, add a scab (like a piece of 2x6 or 2x10 along side the joist with adhesive on the top edge (against the subfloor). This isn't the prettiest, but sometimes handles the squeak.

  5. #5
    Quote Originally Posted by BOB OLINGER View Post
    Yes, squeaky floors are the result of the sub floor inadequately attached to the floor joists. have someone walk on the floor above as you listen and watch from below for squeaks and movement. If you can spot the location
    Install pocket screws from below

  6. #6
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    I thought floor bracing was a western thing for sesimic rollover prevention. Supposed to be the outer three joists. and then in groups of three.
    Bil lD

  7. #7
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    If possible a simple fix that can greatly stiffen your floor without the work of cross bracing after the fact is to simply attach a band/bands of strapping or furring strips to the under side of the joists butted tightly together and running continuously from sill to sill. The cross bracing stops the joist from rolling slightly as it deflects. When the joists roll a a little bit the floor deflects and acts like the skin of a drum. You'd be shocked at how much a single run of furring down the center of a span will stiffen a floor. Its pretty impressive. If your span is of any length you could run two but it'd have to be a long span to make it worth while. We always just ran them straight down the center.

    Its pretty common with tall I-Joist/long span floor systems to get some bounce in the floor and adding that single run of strapping will make the floor feel like concrete.
    Sometimes I just want to look at pretty pictures,... Thats when I go to the Turners Forum

  8. #8
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    Simpson makes metal bracing you might be able to use. Small profile, fairly easily attached.
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  9. #9
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    Squeaking floors & joists that flex are mostly mutually exclusive. Screws & glue will cure the squeaking. Bracing will help with flex. I have engineered joists the were properly sized, but there was more flex than I liked. It was a pretty simple task to install cross bracing, using construction adhesive and screws. I was amazed at how much it stiffened things up.

  10. #10
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    I've seen the old, wooden cross bracing that squeaked. They are not needed if the joists are properly sized.

  11. #11
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    Quote Originally Posted by Bill Dufour View Post
    I thought floor bracing was a western thing for sesimic rollover prevention. Supposed to be the outer three joists. and then in groups of three.
    Bil lD
    It's required here, too...stabilizes for flex, especially since spans tend to be longer these days than "back in the day" because folks don't want posts and bearing walls in the middle of things.
    --

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  12. #12
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    We have come behind many "properly sized" engineered floors that were well suited for a bottom band. Engineered floors (and any floor) that are frequently pushed to their span limits can have a resonant frequency to them when someone is walking across that will actually make people disoriented and nauseous but they are completely within spec and deflection limits. The simple strapping trick on the bottom side turns the floor into a rigid mass. Its akin to a mini torsion box. I never would have believed it until the first time we did it. Its truly impressive. I dont think I installed a dimensional floor joist in the last 10 years of my time in the field and we used that trick exclusively. Its WAY faster than cross blocking or bridging between joists and it eliminates a million fasteners which are all potential squeaks. A floor that doesnt move doesnt squeak whether its screwed, nailed, glued, or any combination.

    I will take a single run of furring from sill to sill over any form of cross bracing any day.
    Sometimes I just want to look at pretty pictures,... Thats when I go to the Turners Forum

  13. #13
    My house from 1910 has x braces every 10 feet or so on 2x10 joists. The floor squeaks. Frankly it has never occurred to me to do anything about it.

  14. #14
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    Quote Originally Posted by Mark Bolton View Post
    If possible a simple fix that can greatly stiffen your floor without the work of cross bracing after the fact is to simply attach a band/bands of strapping or furring strips to the under side of the joists butted tightly together and running continuously from sill to sill. The cross bracing stops the joist from rolling slightly as it deflects. When the joists roll a a little bit the floor deflects and acts like the skin of a drum. You'd be shocked at how much a single run of furring down the center of a span will stiffen a floor. Its pretty impressive. If your span is of any length you could run two but it'd have to be a long span to make it worth while. We always just ran them straight down the center.

    Its pretty common with tall I-Joist/long span floor systems to get some bounce in the floor and adding that single run of strapping will make the floor feel like concrete.
    Like the rat boards on a roof. No need to butt joint. Just overlap across two joists. I suppose even one joist side by side may work..
    Bill D

  15. #15
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    We had new vinyl flooring installed this week and had the flooring guy work on the squeaks first. He installed a few screws and it's quiet now. But It could come back so I plan to do more from below.

    Here's the thing some do not understand about X bracing. It creates a truss across the floor by supporting every joist from the adjacent ones. Without it, when I step from one joist to the next the movement works the subfloor fastening. The strap will really help and I'll do at least that but probably will use a 2 x 4 well screwed to each joist. It will tie them together vertically.

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