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Problems with Floor Vibation/Deflection

motherof3sons
10 years ago

We have been in our home for 16 months and notice what we call a "bounce" in the floor. The area is an open concept with kitchen, dining and living room. The floor was developed by a structural engineer and is comprised of approx. 12" engineered ijoists.

The company making the joists recommended another ijoist be cut and placed between each floor joist 9' from the wall. The recommended remedy simply did not work. When we walk through our kitchen, there is still a significant "bounce" in the floor.

The lumber company responses have been: "it's a vibration and there is nothing we can do" or "you need more weight on the sysem." I understand vibrations can travel through hard surfaces (hardwood), but I do not understand that we need more weight. This indicates to my non-engineer brain that the ijoists are not performing.

We have put on hold the repair until this can be resolved. Any thoughts or ideas? Your assistance is greatly appreciated.

Comments (15)

  • renovator8
    10 years ago

    The building code (and accepted engineering practice) long span joists to defect more than the point where the floor system shakes which is quite uncomfortable when someone is sitting and reading and another person moves quickly across the room.

    The floor system is structurally sound but still very poorly designed. There are no charts for this design issue; the designer simply needs to know what works.

    If the repair you mentioned is blocking at 9 ft from the wall I'm not surprised that it did not work since I-Joists are pretty resistant to twisting when loaded.

    What you need is a stiffer floor. Is the floor exposed from below? Are there a lot of wiring and plumbing pipes penetrating the joists? If not, you can sister the existing joists. You could also add a continuous 2x4, metal plate or metal angle to the bottom of each joist or add full height X 8-0 long pieces of 5/8" thick plywood to the sides.

  • renovator8
    10 years ago

    There is no way to calculate or set limits for bounce so an engineer has no more expertise than an architect or builder.

    At this point it is a matter of adding stiffness to what is already built and that is a practical problem that is best done by an experienced carpenter looking at the existing conditions. Depending on the piping and wiring, some solutions are possible and some are not.

  • dekeoboe
    10 years ago

    Is the floor hardwood or tile? If tile, did you use natural tile?

  • nightowlrn
    10 years ago

    I feel for you. Our first house had a bounce. It was annoying. We didn't try to fix it as we didn't plan to stay long. Even the dog running across the room would get it going ... very annoying.

  • motherof3sons
    Original Author
    10 years ago

    Thank you all for your responses.

    The room below is a finished guest bedroom. The washing machine leaked and water went everywhere. At this time the ceiling is exposed. The room above is the kitchen with hardwood floors.

    In the ceiling of the guest room contain water lines to two sinks, exhaust for the dryer and adjacent bathroom, and a heat run.

    One contractor recommended cross braces, but the lumber company contacted the engineer and they wanted to use the ijoist blocking. Of course they did! It is their product. I am a bit sarcastic. My apologies.

    One of the longtime lumber company reps and former builder told us we don't have enough weight on the floor. I don't buy that. The kitchen has granite counters, double ovens, SZ frig, island, etc. There is a lot of weight in that room.

    Nightowlrn - I know what you mean! My 30 lb 2 year old grandson can make the floor move.

    Again, thank you for your responses. We have put the water damage on hold until the "bounce" is resolved.

  • renovator8
    10 years ago

    The cause of the bounce and vibration is excessive deflection because the joists were not sized to prevent it although they may meet the minimum requirement of the building code. Blocking and additional weight is too little too late; the joists must be made stiffer.

    Adding additional joists is usually impossible without removing and reinstalling plumbing and wiring and even then getting them in is often impossible.

    The plywood gussets on the sides of the joists is probably the best solution but it can only be used where there are no pipes, etc. But the gussets don't need to be on every joist. Reinforcing 2/3 of every other joist might be good enough.

    Plywood is made as long as 10 ft. Make a sketch of where the obstructions are and post it here.

    Photos would help.

  • bus_driver
    10 years ago

    Span tables typically show deflections of 1/360 of the span with options of deflections of 1/480 of the span. Some vertical movement with dynamic loading is unavoidable. Blocking/bridging between the joists may indeed help as it transfers any vertical movement of one joist to the adjacent one on each side.

    Here is a link that might be useful: Bridging

  • bus_driver
    10 years ago

    For an easy understanding of deflection, divide the length of the joist span in inches by 360. Thus a 12' span (144") divided by 360 shows a deflection of 0.4" - more than 3/8". Surprising, huh?
    Some of the engineered joists have span tables for lesser deflections.
    Using larger joists and/or closer spacing than the tables is always permissible.

    Here is a link that might be useful: span tables

  • renovator8
    10 years ago

    Deflection limits are for full design loading and don't tell you much about bounce with a much lighter load.

    L/360 is used to avoid ceiling cracking with dimension lumber joists. For longer I-Joist spans the deflection limit is more like L/720in order to reduce the risk of bounce.

  • motherof3sons
    Original Author
    10 years ago

    Thank you both for the responses. The structural engineer is coming tomorrow. I do not believe there is significant deflection. None of the finished ceilings show any signs of cracking. The house is 17 months old.

  • renovator8
    10 years ago

    Deflection that causes a bouncy feeling in long span joists cannot be seen and it is not a structural concern nor will it ever cause cracking. Don't confuse the deflection limited by structural design with the shake of a long span joist. There are no tables that tell a designer or engineer how stiff a joist must be to avoid bounce.

    The engineer needs to understand that you want to make the floor joists stiffer for better comfort. I would avoid the word "deflection".

    If there is clear space for plywood gussets that is the obvious answer but only someone who has seen the conditions can tell you if that is feasible. You might only need to reinforce a few joists near the middle of the room.

  • Donna Mangold
    2 years ago

    I have this same problem in new construction. Did Motherof3sons ever get the bounce resolved?

  • HU-485040411
    last year

    @Donna Mangold or @Motherof3sons - how did you resolve the issue? I have a similar issue with new construction and am not sure if I should go ahead with the purchase.

  • seosmp
    last year

    Following