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Thread: Cross bracing floor joists

  1. #16
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    Quote Originally Posted by Tom Bender View Post
    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.
    That's right Tom. Strapping across the bottoms of the joists will help, but not nearly as much as cross bracing. It will do nothing to spread the load from one joist to the adjacent joists, which cross bracing will do. It's simple physics and there's no arguing with that.

  2. #17
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    Why no mention of solid blocking? Just cost? Seems easier to retrofit blocking
    Bill D.

  3. #18
    Quote Originally Posted by Bill Dufour View Post
    Why no mention of solid blocking? Just cost? Seems easier to retrofit blocking
    Bill D.
    Because of utilities that are usually in every joist bay.

  4. #19
    Solid blocking, no different than cross blocking, while it helps, its not as good as the sill to sill, tight but joint strap, on the bottom. Its slower, it will never be super tight in every bay, results in a ton more fasteners all of which have the potential to also squeak or allow deflection.

    Of course if the sheathing is loose, no amount of blocking is going to solve the problem and screwing, toe-screwing, trying to push adhesive to the sheathing/joist connection are all sound attempts at a fix.

    But if adding some rigidity (which is never a bad thing for a squeaky floor) is the goal, the simplest, fastest, and most effective way is the butted strap from sill to sill or to some solid termination point. Joists dont deflect vertically, they roll, thats the purpose of the blocking, so the strapping option eliminates the roll transferring any possible roll to all adjacent joists and straight out to the sill. At that point you have a floor system thats doing what its suppose to. A load, whether it be static or a person walking across the floor, is firing multiple joists as opposed to just 2-3 right around the load.

  5. #20
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    Quote Originally Posted by Günter VögelBerg View Post
    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.
    In some cases floors are made to be squeaky:

    Squeaky Floors.png

    It would be neat if it could be engineered to play a tune as one walked over the floor. Are there any palindrome tunes?

    Google > nightingale floors <

    jtk
    Last edited by Jim Koepke; 01-22-2020 at 1:42 PM. Reason: nightingale floors
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  6. #21
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    Quote Originally Posted by Walter Mooney View Post
    Simpson makes metal bracing you might be able to use. Small profile, fairly easily attached.
    Absolutely agree!
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  7. #22
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    Cross bracing, properly installed, will be much stronger than a simple furring strip attached to the bottoms of the joists. Of course, Mark doesnt specify how many furring strips he is installing or what spacing they are, or for that matter what dimension the furring strips are (1x2, 1x4, ??) and how they are fastened.

  8. #23
    The answer is one. Mid-span, sill to sill, tight but joints, fastening of your choice (no need for any goofiness like glue). What your missing is that your simply reproducing what youve always known. Wood or metal cross bracing (which I havent seen installed in perhaps 20 years or more). The point of metal or wood cross bracing was to reduce the roll of the joist because that is the first stage of deflection. The joist doesnt deflect straight down until all roll is completely eliminated (which is impossible because then you have a solid mass or a torsion box).

    The single run of strapping run from sill to sill, or some other laterally rigid stopping point achives the exact same thing with gobs of hours less in labor, way less fasteners (all of which are squeak potentials) and far less costly materials.

    A joist system deflects like a comb or a pad of paper. Load at the top, rolls the joist members below radially away from the load which allows deflection and bounce. If you eliminate any potential for roll you drastically stiffen the floor because now you are dealing more closely with vertical deflection only.

    This has become more and more common with engineered floor systems carrying longer and longer spans with taller members (I joist that are 12", 14", 16" tall). Similarly floor trusses though the roll is a bit less because of the cross sectional width of a common floor truss. But the same thing applies to a 2x6 or a 2x8. They all initially deflect/fail by rolling.

    The cross bracing helped this by connecting the top of the adjacent member to the bottom of the next. Perfect sense. Same as connecting the bottom of every joist in the pan to the outer sill or some other rigid termination that will eliminate the roll from the entire joist system.

    Its super simple. And it works flawlessly. Ive done it dozens of times. Contact TJI, LP, BCI, Red-I, dont take my word for it.

  9. #24
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    Quote Originally Posted by Mark Bolton View Post
    The answer is one. Mid-span, sill to sill, tight but joints, fastening of your choice (no need for any goofiness like glue).
    Sorry, but I still don't quite understand what you're suggesting. One furring strip across the joists at right angles or a furring strip under each joist? What size furring strip?

  10. #25
    One. It would have to be perpendicular to the span? No? Any size you want. Furring or strapping is typically 1x3 but common to be 1x4. Size isnt really an issue. The strength comes from the butt joints longitudinally.

    Extremely simple

  11. #26
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    Joists sag in two ways, they roll and they flex. A metal or light wood strap will reduce the roll but will do nothing for flex. The sag may be only 1/16" as I walk from one 'free' joist to the next but that is enough working of the subfloor to make the nails squeak. My intent is to install a 2 x 4 flat across the bottom of the joists, creating a suspended beam. This will cause my weight to be transferred to the adjacent joists so they sag together and sag much less.

    A more substantial suspended beam would be even better but not wanting to give up too much headroom I'll just do the 2 x 4.

    Thanks for all the comments, this has helped me think thru the matter.

  12. #27
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    Yes, strapping across the bottom can eliminate buckling or "roll", but does little to transfer the vertical load from one joist to the next, which will stiffen the floor. One facet of structural engineering is all about triangles. That is why diagonal bracing, whether wood or steel, is the best way to go, but of course the issue is getting around duct work. Solid block bracing will achieve the same advantages. Something that simple strapping across the bottom of the joist will not. Plus that strapping will reduce ceiling height by the thickness of the strapping. Now if the strapping were, say, a vertical 2x4, then you would be transferring load from one joist to the next, but that is not practical. A flat 2x4 will start to transfer some load, but not nearly as well as diagonal bracing or full depth blocking. Is it better than nothing? Yes.
    Last edited by Ole Anderson; 01-31-2020 at 9:20 AM.
    NOW you tell me...

  13. #28
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    Quote Originally Posted by Tom Bender View Post
    Joists sag in two ways, they roll and they flex. A metal or light wood strap will reduce the roll but will do nothing for flex. The sag may be only 1/16" as I walk from one 'free' joist to the next but that is enough working of the subfloor to make the nails squeak. My intent is to install a 2 x 4 flat across the bottom of the joists, creating a suspended beam. This will cause my weight to be transferred to the adjacent joists so they sag together and sag much less.

    A more substantial suspended beam would be even better but not wanting to give up too much headroom I'll just do the 2 x 4.

    Thanks for all the comments, this has helped me think thru the matter.
    A 2x4 across the bottom of the joists will do very little to transfer any load from 1 joist to the next. You need cross bracing or solid blocking to achieve that. And cross bracing will cost you no headroom at all. I installed it in my basement and it isn't hard at all to do.

  14. #29
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    Strapping does nothing to prevent roll over. AFAIK blocking or x bracing is required in the west for sesimic reasons. Without blocking I have seen houses that rolled over all the joists. Damage does not look too bad from outside just the siding at floor level is splintered. Bolting to foundation does not prevent it. I do not think wind loads ever get strong enough to do it on a proper house, maybe on a shack, tree house.
    Bil lD

  15. #30
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    A 2x4, laid flat across the joists, glued and screwed to each joist, is not adding significamt strength to resist vertical motion. If vertical motion of the joists is the culprit then your joists are undersized. Better off doubling them up by sistering a 2x4, or better yet a 2x6 with glue and screws, to the face of each joist that is concerning.

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