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Re: bouncy existing floor joists

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        Following are some things you might consider to improve the "springiness" of your floor are the following.

       Assuming the drywall is OFF of the underside of the floor.

1.)    Add bridging to improve the load sharing properties of the system.  Three rows of solid block or X bridging should help a lot.

2.)    Change the system to a "stressed skin" system by adding 5/8" T&G plywood glued and screwed to the underside of the joists.  Span the plywood face grain in the same direction as the 2x10 (not across the joists).  Glue all T&G joints plus backup the end joints.  This should approximately double the EI of the joists, hence reduce deflections by 50%.

3.)    If you wanted to remove the concrete topping you could add plywood to the top as well.  Adding plywood to both top and bottom should approximately triple the EI of the joists, hence reduce deflections bu 66%

4.)    Replace the drywall to regain the desired fire resistance.

        Note:  These recommendations should solve the structural problem, however, adding plywood will add to the combustible material in the system and may affect whether this would meet the fire code in some jurisdictions.  You are on your own for this.


H. Daryl Richardson

"D.A." wrote:

HI I have A problem A custom home built in 1980's with 2x10 floor joist  at 12" on centerit spans 18 feet long the floor has 1 1/2" light weight concretethe owner try to remodel and want to stiffen  the floor system because is very bouncyand vibrating even it has dry wall at bottomso the dry wall pulled off and just added 1 3/4 x 91/4 PSL 2.0 E. at 12' on center .no dry wall added yet and the floor still bouncy and vibrating1- is it possible after adding the dry wall will be ok2- what other solution can be done without adding beams or increase the depth of floor joists    because adding a beam will be deeper and too big due to long span where possible to    add post.3- is it adding steel tube joist at 24" will solve the problem thank in advance for any adviceDave A. P.E.