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Sister 2 X 4’s to Floor Joists to Stop Plywood Subfloor Squeaks

jimmiem | Posted in Construction Techniques on July 14, 2014 06:40am

I’ve removed wall to wall carpeting from a first floor room (over an unfinished basement) in order to install 3/4″ solid hardwood flooring.  The 3/4″ t&g plywood has squeaks and I have (1) removed all the smooth shank nails that were used and replaced with #8 2″ SPAX screws. (2) cut a 1/8″ groove through the t&g joint that was installed tight and seemed to be the squeaky area  and added braces from below to support this groove. I still had squeaks.  The plywood over one joist was the worst when I put all my weight on the joist and bounced.  I stood a couple of long boards on the basement floor (one on each side of the joist) and wedged them against the subfloor.  This stopped the squeak and helped quiet a lot of the other squeaks.  Should I sister 2 X 4’s to the sides of each joist to take the movement out of the subfloor?   Do you think that replacing the 2″ screws with longer screws might solve the problem?  The plywood was installed with construction adhesive and there are no gaps to add shims.

 

P.S. I started this post under General Discussion under Squeaky Plywood Subfloor but I think it ran its course.          

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  1. User avater
    deadnuts | Jul 15, 2014 07:18am | #1

    double check for nails

    Deflection + nails = squeaks. Taking deflection out of the equation can achieve your goal, but longer screws probably won't help that much. Sisterig with 2x4's is questionable as well. What is the span and size are your joists?

    Sounds to me me (pardon the pun) like you might have missed pulling some nails which could still be the culprit. I would make sure to rule this out before adding lumber.

    1. jimmiem | Jul 15, 2014 11:40am | #2

      Doubled Checked for Nails

      I doubled checked for nails.  All the smooth shankers are gone.  There are a few spiral nails they must have added near the tight t&g  joint ( I had relieved this with a 1/8" cut) .  I pulled one spiral nail and gouged the area so I left the other 2 alone.  I reset some of the screws that I added and relocated a few.  Still had some noise.  There are a couple of joists that are the noisiest.  I just installed temporary bracing from the basement floor up against the subfloor right beside the  'noisy' joists and this eliminated a lot of the squeaks.  Joists are 2 X 10.  Span is 12 feet.    I think I've been at his too long....I just got your pun after re-reading it 3 times. My wife has even started asking what's going on?

      1. User avater
        deadnuts | Jul 15, 2014 07:13pm | #4

        get after ALL those nails

        I'd pull all the nails--including ring shanks. Drive a cats paw down in there and grab the head. Be the boss; don't let those nails beat you. It doesn't matter if you gouge the floor. It's not finish materail...and you're covering it up with new flooring. Gouges are not going to compromise the structure of the floor to any appreciable degree either.

        You have to look at it this way: What else could be sqeaking? It's got to be the nails you missed. Wood on wood can squeak; but not likely. That usually happens only with hardwood edges that are butted tight and joints have been cut at 90 degrees with finish finish blade that makes the end grain super smooth. That is one reason (the main reason is tight fits on face side) why hardwood flooring is milled with slight backcut angles on all t&g joints. Anyhow wood on wood squeaks for subflooring materials is rare.

        If you are intent on sistering because you just feel your floor has too much deflection (remember; the hardwood floorig will stiffen it as well), then I would use at least 2x6 (I'd opt for 2x8's if you can afford it) and set new joists flush with the bottom of your 2x10's. I would glue them together with PL and lag or carriage bolt them together. Some folks just  nail the crap out of them to develope composite beam action, but then you risk nail squeaks there as well. No sense going from the pot to the frying pan; right?

        1. jimmiem | Jul 16, 2014 10:34am | #8

          Subfloor Noise

          I'll pull them.  At this point the noises are more like the creaks you get when you walk on a hardwood floor that is not dead tight. If I walk from joist to joist I hear the noise (not a squeak) when I transfer my weight.  With the basement floor braces those noises did not happen and the subfloor had a more solid feel when I walked on it.  I see some construction adhesive on the sides of the joists in these noise areas.  Could the original subfloor installers have messed up when they applied the adhesive?  They used smooth shank nails, butted the t&g and the end joints tight, sistered a 2 X 4 in another room to support the end of a piece of plywood that didn't reach the joist and didn't use construction adhesive which left a gap that I had to shim.  Lots of sub-par work? 

          One more quick story.  My builder built 15 houses in this development.  There has been a local handyman who has been working full time for homeowners in this development for YEARS.  I was chatting with this handyman recently and this subject came up.  He started laughing and said that a couple of years ago he sent a holiday card to the builder and included a note thanking the builder for providing him with all the fix-it work.          

          1. User avater
            deadnuts | Jul 16, 2014 12:22pm | #9

            couple of further thoughts to consider...

            JIMMIEM wrote:

             With the basement floor braces those noises did not happen and the subfloor had a more solid feel when I walked on it. 

            I'm not surprised. With the posts/braces in place you have direct bearing.... and/or have effectively cut the joist span down substantially. Like I side, if nothing moves, then nothing squeaks.

            The reason I harp on pulling ALL the existing nails is because once you lay your floor you won't have this avenue to attack the issue any longer. At that point it's only  blocking and sistering(or posting) at your disposal to address the problem (or live with it). Might as well do as much as you can with removing the nails now because it's the cheapest solution. Plus, the laying of the new floor  might alleviate the problem* as well. You can always do the sistering later to improve the situation once the floor is laid.

            BTW installing full height blocking perpendicular to your joists at mid span (or two rows at 1/3 span) will stiffen your floor as well. Install those with PL and pocket screws. Again, anything you can do to limit movement will limit your squeaks.

            *new hardwood flooring and nails help develope shear strength between sub and finish floor thereby reducing deflection (movement) in the floor diaphragm. You might think flooring nails would add potentail squeaks, but that's generally not the case. The acute angle of flooring nails (or staples; but I like the serrated flooring nails) with deformed edges help prevent that from happening.

          2. jimmiem | Jul 16, 2014 01:10pm | #10

            Thank You

            I understand your point about the nails....especially  with the type that was used....can't go back and pull them later.  I'll pull the spirals and install the flooring.  If anything is needed after that I'll block or sister as you suggest.  

  2. DanH | Jul 15, 2014 06:38pm | #3

    How many layers of subfloor do you have?  Our house, typical for 1976, has 3/4" plywood topped by 1/2" "underlayment".  Using 2" screws would leave less than an inch penetrating into the joists and not do a lot to end squeeks.  I've always used something closer to 3" in this house, when going after the squeaks.

    1. jimmiem | Jul 15, 2014 07:19pm | #5

      Subfloor Layers

      House was built in 1988. All the rooms that had wall to wall carpeting, including this one, had 1 layer of 3/4" t&g plywood subfloor.  The kitchen area which has a sheet vinyl finished surface has a 1/2" plywood underlayment in addition to the 3/4" t&g plywood subfloor.  The  nails used throughout the house to secure the 3/4" subfloor were 2".  This room was a real squeaker and I pulled all the smooth shank nails and secured subfloor with #8 2" Spax screws.    The basement floor to subfloor supports eliminated almost all the squeaks.....so I thought sistering these areas might do the same.

      1. User avater
        deadnuts | Jul 15, 2014 07:52pm | #6

        2" nails used were short anyhow

        As a general rule of thumb the fastener length for nails should be 3x's the thickness of the  material you're attaching. That is why most 3/4" subfloors were traditionally nailed (attached) with 8d CC sinkers. Those nails are 2-3/8" long.

      2. User avater
        deadnuts | Jul 15, 2014 07:52pm | #7

        2" nails used were short anyhow

        As a general rule of thumb the fastener length for nails should be 3x's the thickness of the  material you're attaching. That is why most 3/4" subfloors were traditionally nailed (attached) with 8d CC sinkers. Those nails are 2-3/8" long.

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