Spongy 2nd story subfloor

Discussion in 'Floor Preparation' started by BillFjr, Nov 2, 2010.

  1. BillFjr

    BillFjr New Member

    I have a spongy second floor in a home built in 1995. Joists are engineered wood I-beams per the builder. I don't have direct access, but from associated measurements I believe the I-beams to be 11 to 11.5 in. tall. I pulled the carpet and found the joists to be 22-24 in. OC.

    The subfloor is 3/4 in, and appears to be common plywood with the rough side up. Nail spacing varies from 12 to 18 in. apart on joists, plus the subfloor does not appear to be glued. From various manufacturer sites it seems the max span for this size I-beam can be up to about 16.5 ft. My game
    room has a span of 15.5 ft and is 23 ft. long, other rooms have a 13ft. span. I contacted the builder about my spongy issue, naturally the warranty supervisor said all was a-okay, within specs. From a safety standpoint I'm sure he is spot on, from an agravation standpoint the builder is way off base.

    Everything shakes and rocks from normal walking. All rooms on second floor have normal bedroom furniture, nothing heavy, no aquariums, etc. The gameroom has a 4x8 1in slate pool table. Foot drop noise is prevalent as well as subfloor squeaking. Some parts of the floor feel very uneven, some parts
    more spongy than others. Most spongy area is where the stairs meet the second floor.

    1) Examine uneven areas, if bad then fix, but not clear on how.
    2) Secure subfloor with 1 3/4 #8 screws, 6 in. OC.
    3) Cap with 4x8 3/8 in. Plytanium or comparable plywood.
    4) Squirt back of cap with Green Glue to reduce foot drop noise.
    5) Secure Cap with 1 3/4 #8 screws, 6 in. OC throughout the subfloor field.
    6) Lay new carpet with heavy pad.

    I'm still thinking about using a heavy (1lb/ft) rubber/vinyl type sound deadening pad, or 2lb/ft sandwich
    type pad instead of the Green Glue in step 4 but concerned about the additional weight and compromising its
    effectiveness with so many screw holes.

    The reason for 3/8 in. cap in lieu of 3/4 in. is that the top stair will have an increase in riser height, all doors
    can accomodate increase.

    Does this all sound acceptable, or does anyone know a better way, product, etc.?
  2. Tandy Reeves

    Tandy Reeves Resting In Peace Charter Member I Support TFP Senior Member

    It appears you are having to do some guessing about the joists and subfloor.

    In my opinion, you need to open up the subfloor and see exactly what you are dealing with. Also, the first thing I would do is determine how much deflection in the floor you are dealing with. It does not sound like there is a simple fix the the problem. Adding something on top is not going to solve the problem.
  3. hookknife

    hookknife Hard Surface Installer Charter Member Senior Member

    Id call the builders bluff, there is no way that a floor you walk on should be that unstable. Id hire my own personal inspector to make sure things are up to code, and that the plumber etc didn't cut into the joists and compromise their structure. I also think the problem should be dealt with from the bottom up instead of a band aid.
  4. amirpawn

    amirpawn Pro Member

    i have seen some extreme cases where they ran those fancy new i beams over a 40' span--kinda cool--an entire basement without any lolly columns---the problem---the floor was a trampoline---and sadly enough it did pass minimum building code---the solution there was support underneath---aka-lolly columns----i dont pretend to know what the solution might be on floor 2---not even sure that it is the problem here---this is not a flooring issue--there is no flooring that will fix it--a lot of the builders bought the hype and now dont know what to do--they will swear that nothing is wrong since it passes code and they wont fix what is not broken-- i hope i am wrong and i wish you all the best
  5. Sean Moore

    Sean Moore Pro Member

    This is the truth. This is a problem for a structural engineer.

    You might mitigate it but if it's bouncy there is no flooring solution that will alleviate it.
  6. Peter Kodner

    Peter Kodner Inspector Floors Charter Member Senior Member

    As others have said, a flooring or addition to the subfloor will not correct the condition you have.

    Lam beams, pre-made truss and other engineered joist systems have greatly increased load ratings, both static and live, over timber or boards systems. This has not been a good thing for finished floorings (except carpet) as they invariably are designed to stiffen as load is applied, i.e. they must move to increase in weight bearing capacity.

    The other problem they create is due to the increased load rating, the are spaced further apart. What used to be 16" centers on board systems is not 19.2" or 24" O.C. I have even inspected a couple jobs where the were 30"!!! A 19.2 center usually does not exhibit much more movement than a 16, but 24 most assuredly do. I believe I can make a determination of this before looking at the system by just walking in a home with 24" centers.

    I am quite sure you construction will be your local code but I'm unaware of any remediation that can be done for your condition short of pulling the subfloor and cross bracing all the joists.
  7. Daris Mulkin

    Daris Mulkin The One and Only Charter Member I Support TFP Senior Member

    What about bridging?? Wasn't there something on how to make bridging after the fact on here a while back? Or even screwing in plywood to the side of the joist in the spongy areas? Of coarse this would have to be done from the top removing the flooring.


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