Bouncy joists

Discussion in 'Flooring' started by cmerk16, Apr 9, 2012.

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  1. Apr 9, 2012 #1

    cmerk16

    cmerk16

    cmerk16

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    Is it necessary when trying to eliminate bouncy Joists to use 3/4 inch plywood or can I use half-inch?

    Reason I ask is because I have a bunch of half inch sheets left over and was thinking about just using that since I had it. And then by 3/4 for where I need more.

    Or just double up on the half-inch on both sides of the joists and buy 3/4 when I run out?
     
  2. Apr 9, 2012 #2

    isola96

    isola96

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    What is going over the floor? All subfloors in my book should be at "least" 3/4" for anything other then tile 1" of wood. But if this is cost to you double up on the 1/2" you won't have any bounce, just make shore your not to high from other rooms by doing this.
     
  3. Apr 9, 2012 #3

    nealtw

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    I would think the half inch plywood wood help. Have you measured the bend that you are getting now? If you run a tight string from wall to wall an inch above the floor you can measure how much it moves when you walk on it. Do up a few joists and see how well that is working.
    On another thread Bridgeman suggested a 2x4 on flat glued and screwed to the bottom of the joist and he had all the numbers on how much stronger the joist would be.
     
  4. Apr 11, 2012 #4

    Jaz

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    Just to clarify for isola96, (aka Jet) the OP is talking about using ply strips to sister the joists, not as a subfloor.

    Jaz
     
  5. Apr 12, 2012 #5

    isola96

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    tushay!..... Jaz, another check mate on me.

    I personally don't think that will remedy much since there strips now 2x4s better and cat them even "betterer"! Lol
     
  6. Apr 12, 2012 #6

    00Mike

    00Mike

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    "Is it necessary when trying to eliminate bouncy Joists to use 3/4 inch plywood or can I use half-inch?"

    Was the structure built to code? If so, there shouldn't be a bounce. I just built a two story 2.5 car garage using my own design. Prior to building I researched on line for building codes regarding joist spans for live loads. I found that, to meet code for my situation, I had to use 2x10x12s - 16"o/c - supported by 4 glued up 2x12x16s - which were themselves supported by 2 jack posts equally spaced down the length of the garage. There was no bounce prior to installing the 1/2" plywood and it's solid as a rock. The alternative was to use 14" high laminated I beams which was unacceptable.

    If you're not concerned about walking on the deck you don't need to be as critical but I don't think that plywood, by itself, will give you the results you're looking for. Plywood may greatly reduce the amount of bounce but, if the framework was under-built, it may not be a satisfactory solution.
     
  7. Apr 12, 2012 #7

    nealtw

    nealtw

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    OOMIKE; Was there a suggestion in there , or should he just rip it down and start over?
     
  8. Apr 12, 2012 #8

    isola96

    isola96

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    Well I don't think it's the joists.
    We're any parts of the floor sagging?
    Your going to have bounce if you put 1/2" ply down plain and simple.
     
  9. Apr 12, 2012 #9

    nealtw

    nealtw

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    isola. He is talking about beefing up the joists not putting down 1/2"
     
  10. Apr 12, 2012 #10

    isola96

    isola96

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    Yes Opps?!... Post withdrawn
     
  11. Apr 12, 2012 #11

    00Mike

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    Sorry, I wasn't trying to offend. A major component of my day job is problem solving. I would never tell someone to tear it down and start over. There's almost always a solution. However, since I don't know the particulars, it's difficult to give a suggestion. What are you using for joists? How far apart are they? What are the spans in each direction you are working with? What is the purpose of the space (its intended use)?

    To meet code for live load using dimensional lumber I had to use 2x10s and I had to keep spans in both directions to 12' or less. The "suggestion" I was trying to get across in my last post was that, if you used something less than that, you will need more support. Plywood in the flat is not the answer.

    Not having any of the particulars, here are some suggestions:

    1) Is it possible to run a beam (or beams) under the existing floor joists to increase stability prior to laying down the 1/2" ply? Here's a link to a span calculator: https://courses.cit.cornell.edu/arch264/calculators/example8.1/index.html. You can cut and paste it into your browser. It will give you an idea of where you need to be at so you have a starting reference point.

    2) Another way to beef up the joist is to take aspenite (or some of your existing 1/2" if you have enough), rip it into strips (wider than your existing joists) glue it to your joists and sandwich another 2x (on edge) (and glued) along the bottom portion of the plywood. The objective here is to increase the depth of the existing joist.

    3) Is it possible to sister wider 2x's to the existing joists to add depth?

    4) Do you have a center beam that could be supported with jack posts or some type of pillars?

    Those are some thoughts. I know you're probably looking for a less expensive and easier option and if you decide I'm nuts that's OK but make sure, prior to laying the plywood, that you use construction adhesive. That will add strength. Having said that I must again point out that, if the joist are bouncy with nothing on them, the concern is what happens as you add load? As you increase the load on the joists (that includes the weight of the 1/2" or 3/4" plywood, flooring, furniture, kids, wife, dog.... it all adds up) at some point down the road, depending on the intended use for the space, the under engineered structure will fail. That's why they have building codes. I'm not saying that to insult you. I'm not much of a diplomat but I am trying to help. My final "suggestion": Take the opportunity to beef it up now before you move on to the next phase of construction.
     

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