So, we’re renovating an attic. We had them put in 3/4″ T&G plywood as a subfloor, supposedly glued down and fastened to the floor joists with ring nails.
Unfortunately, through bad planning or whatever, there were quite a number of places where they had to cut up sections of the floor and then renailed them. So, some of the “seams” between the plywood sections now are not connected with T&G and have considerable movement between them; e.g. if I stand on one side of the “seam” the floor will flex 1/4″ – 1/2″ between the two pieces.
So, what’s the best solution to this? Will nailing/screwing down the boards that move help?
Or, should we explore putting in another layer of subfloor on top of the existing 3/4″ subfloor? I hate to raise the floor up anymore, as that is going to make the stair transition a bit off. But, we’re going to put down hardwood floors eventually and that floor needs to be rock solid.
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When they pulled up and put back was the time for the right fix - to put blocking in at those joints missing the tongue.
and that much flex scares me anyways. That is inconcieveable for 3/4" on 16" centers. What is the framing layout ?
The only way I can imagine flexing like that in 3/4 on 16 is if they damaged the snot out of it when they took it up. if it was glued first time around, they may have peeled a whole ply off the bottomside of it. if so, it should have been burnt not re-used.
So It seems like the only option is to cover it again, with glue , and good luck
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I don't think it is 16" centers. It's pretty old construction, with joists that are more than 2" thick, and probably in the 18-20" range between them.
Aha! The old black diamond Cubitic layout!
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Sounds like the new T&G seams are completely off the joists. And the ends that are deflecting are cantilevered out there with no support.
Adding even 1/2 of plywood glued and screwed over the top of the 3/4 would stiffen things up considerably. Just make sure to overlap the joints as much as possible.
So far as the additional height throwing the last step height off on the stairs. If you are putting in new floor, it shouldn't be too hard to shim the flooring as you install it on the stairs to get the riser heights evened out.
Not sure I understand what you mean. The stairs are already in place. So, adding extra thickness to the subfloor above the stairs is going to make the first step down higher. It's probably not enough to be concerned about, just trying to make sure nobody takes that big first step and topples down the stairs.
What he meant was that you can work out the difference in riser hieght that results
from adding a layer of flooring;
Lets say you added a 3/4 " layer to the attic, the first tread down you lay a pc. of 5/8
plywood to shim it up, the 2nd tread gets 1/2", the 3rd gets 3/8", the 4th gets 1/4
and the 5th gets 1/8"
This way the variance is only 1/8" per riser. (I believe code states no more than 1/4")
VARIANCE OF MORE THAN 1/4" IS DANGEROUS IMO!
What's the minimum that supplies any structure? Would 1/4" help at all, if it was glued down? Or do we need to get thicker?
I would go to 3/8" min. and still glue the flooring to it alsoThe glue between ply and gypcrete is to hold ply down in plane and the glue between ply and flooring to prevent the lateral movement and cupping. edit - I was confusing this with another thread where over gypcrete, but the 3/8 glued still applies
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Edited 8/2/2008 12:23 pm ET by Piffin
The contractor wants a chance to come back and make sure all the plywood is nailed down tight to the studs. I'm 100% confident that will make absolutely no difference in the world - but I'll give him a chance to waste his time on his "solution" before I insist he actually fix it. There's no problem with the plywood attachment to the joists. The problem is that they didn't use T&G plywood over the whole floor so whereever there is a seam between two joists the floor bounces.
Celtsfan.
No sub floor should have a seam not on a joist even tongue and groove.
What in the world do you mean by that?On a floor 24' x 24' you can't buy a sheet of plywood large enough for no seams!
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What? The joists only run one direction. Obviously, one should put all the seams that run in parallel with the joists over the joists (although this requires cutting off the T&G unless you are really lucky) but what about the seams that run perpendicular to the joists? Is it really standard practice to put blocking at every seam? I would think the T&G should be sufficient for a short span.
Edited 8/4/2008 4:55 pm ET by CeltsFan
so how goes the battle?
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No developments yet. Spent the last week on insulation. The GC is supposed to be back to look at the floor tomorrow, so we'll see.
Doesn't the plywood run perpendicular to the joists? The 4' on the plywood should be parallel to the joists. 8' should be running across the joists. 3/4" plywood with no tongue shouldn't bounce anyway. If the plywood is running parallel to the joists, it's wrong. The 8' part of the plywood shouldn't be sitting on the joists with the 4' perpendicular to the joists.
Joe Carola
The plywood runs perpendicular to the joists. We have problems with some bouncy seams both on seams perpendicular to the joists, as well as a few that are parallel to the joists.
We have I think a couple of issues.
1) I think in some places, when there would have been a seam that ran perpendicular to the joists - for some reason they didn't use T&G, or the T/G was cut off. The span between the joists is more than 16", so we have a span of 20" or so, that when you step on one side of the seam the floor will deflect and the other side won't.
2) In a few places, they had to cut out a small section of floor for wiring/HVAC/plumbing issues. When they put those sections back in - there was obviously no T&G on all four sides of the "patch" piece. So, that piece is really unsupported.
We have problems with some bouncy seams both on seams perpendicular to the joists, as well as a few that are parallel to the joists.
There's no way you can have a bouncy 4' seam that sits on the joists unless it's NOT sitting on the joist.
In a few places, they had to cut out a small section of floor for wiring/HVAC/plumbing issues. When they put those sections back in - there was obviously no T&G on all four sides of the "patch" piece. So, that piece is really unsupported.
Of course there isn't. There would/should never be T&G on all four sides. Why would there be T&G on the sides that are sitting on the floor joists. That's impossible.
If I cut out a section between two joists, I would;d cut them down the center of the of each joists, so that means I would be cutting out a 16" wide piece. Once I nail it back down that piece will land back down in the center of the joist again and shouldn't move. The front and back of that piece can move, not the two sides that sit on top of the joists.
Joe Carola
He needs to get blocking glued and screwed to span where those seams are
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Piffin's right...Make him block all the new seams, and glue and screw it back down. If that doesn't work, then add another layer.
Span the seams with 5/8" BCX underlayment (for the hardwood) with ring shank nails.
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When I started, we never saw t and g system. Every floor system we did was 1/2" cdx (no blocking at seams) and later they added a 5/8" particle board subfloor. It sounds like the best solution here. Bob's next test date: 12/10/07
Except for that added height adjustment at the stairs.
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All that should have been considered before they laid square edged subfloor plywood. Bob's next test date: 12/10/07
Yes, but if I understand this right, the subfloor was originally laid with T&G ply, then they ripped the tongues to pull some of it back up again, but they failed to add blocking at those seams when they laid it back down.Now my experience tells me that if you pull up ply that had been glued properly, it is missing some material when you pull it back up again, making it thinner, damaged, weaker. So I would probably not re-use it again.But if it was re-useable, that is because they did not glue it down the first time like they were supposed to.And when they did relay the stuff, they should have added blocking with glue to stabilize those seams.But also since this original layout is more like 20"OC, they should have planned the double ply you mention just to get the spans covered without so much deflection.every item covered in this re-hash I just did points to some pretty poor work on the part of the guys doing it.
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So, they came back and worked on the floor some more. It made an improvement, but it is still not up to my satisfaction. I think our only option is to lay another layer of something - glued and nailed - on top of the existing subfloor.
So, my question is, what thickness should we put down? I'm sure we don't want Lauan - as that has no structure to it at all - right? They do have 1/4" plywood, though, correct? Would that do the trick, or would we need to go to 3/8"? Do they make 3/8", or is the next thickness 1/2"?
If you are looking for any degree of structural improvement, I think you need at least 3/8" ply, glued and screwed at 6" OCI also seem to recall you were adding hardwod flooring, which does add to strength and solidity IF you are running it perpendicular to the joists.
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Most floors will be getting hardwood flooring, but some of it will be carpet. I'm most concerned about the carpeted area - obviously.
Use 5/8 particle board or 1/2" plywood at the carpet areas.
The floor is fine the way it is if its 16" centers. I never use t and g subfloor under hardwood floors due to the risk of the tongues telegraphing at the wood floor t and g if they align at the same place which is very likely to happen. The wood will stiffen the floor up with no problems. in fact it could be 1/2' plywood and you wouldn't have problems. I've put t and g oak over hundreds of 1/2" square edge plywood.
Well, I would defer my judgment to anyone that has successfully installed hundreds of wood floors over square edged subfloors.Do the nails actually hold okay in half inch ply? Bob's next test date: 12/10/07
I used to use 1/2" and so did everyone else around here for many years. We all use 1 layer 3/4 now. Never had problems with the oak. We did however have a lot of trouble with how guys came in and put particle board down and other plywwod materials on top of 1/2". Most of them did not pay much attention to breaking that stuff on the joists.
I can't say hundreds, but a bunch, mostly when I've done additions to houses w/ 1/2" in existing house.
I would start off by saying that unless I'm misunderstanding the op., the floor was down, they had to cut some sections up (prolly for wiring, vent pipes, etc.) and these are the sections with an issue. Unless it is as some are perceiving, with the four foot edge unsupported (which I don't think is the case), it shouldn't be a big deal.
First off, as far as blocking goes on a ripped edge, where the ply has been cut perp to joists and is no longer t&g: probly not a bad idea if you are really getting 1/4 to 1/2" of deflection. If the floor was ripped at points such that the filler was a skinny piece, it would definitely be smart.
I've said it before; I'll say it again, houses were built for hundreds of years with 3/4 t&g with NO subfloor, and they were nice and solid, diagonal and perpendicular.the nature of t&g is that it locksit up into practically a solid piece of oak,or cherry or whatever, 3/4" thick. It will span 3/4 t&g solid as a rock, IF the floor joists aren't overspanned, leading to bounce.
If the stairs are in, you're screwed anyhow. I'm pretty fanatic about consistency in rise, and the graduated method described before would never fly with me. If they're getting carpet, then figure the correct rise with the finished oak, and pad each tread acccordingly so they're all the same. You can even throw another layer of 1/2" on the floor if it helps you sleep at night. Waste of $ in my book tho' The first time I had an addy with 1 layer of 1/2" cdx ply for a sub, I was horrified at how badly it sagged between joists(16" oc) how badly it crackled when I walked on it even. Talked to a few mentor types, and laid the oak over. I weigh 245 and I promise you , the floor feels the same as in a new house with 11_7/8" tji's spanning 12 ft with 3/4" advantech. honest injun.
my .02
Bing
Edited 8/6/2008 10:15 pm ET by Bing187
"houses were built for hundreds of years with 3/4 t&g with NO subfloor, and they were nice and solid, diagonal and perpendicular.the nature of t&g is that it locksit up into practically a solid piece of oak,or cherry or whatever, 3/4" thick"That really is not a valid comparison to today's flooring. That old was better grained lumber and full lengths, not the 8"-20" scraps that they seel for flooring now.
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I agree with you that it's not the same, but the trees my oak comes from, I would think, are pretty old. My unfinished oak comes in a bundle of 22 sq ft, and while it does have a few shorts, I don't think that it's more than 3 or 4 ft. I get a lot of 3s and 4s and 6s too. I think that the t&g makes the lengths less relevant.
I'm certainly not implying that a good sub isn't important, but if you take 10 pieces of oak t&g and lay em on a sundeck that's framed, with no decking, bang the tongues tight....... you can jump up and down on it and you'll get more deflection out of the joists than the oak. Add to that that the longer pieces are nailed on the other side of the pair of joists that you stand on at mid span, and you get the same cantilever strength that makes a single floor joist spanning over a beam stronger than two joist lapped at mid span.....
Not trying to start a whizzin contest, but I've seen it enough times in practical application to know it's true.
Bing
I can't remember why but I thought it was better to split the joist over the beam. Sorry for the interruption. Bob's next test date: 12/10/07
Yep. no worth whizzin' over.
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Save the whzzin for the Pol threads. Bob's next test date: 12/10/07
know where I can find a good one? I gotta go.
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There is no such thing as a good Pol thread. I keep making great points and Bob doesn't answer. Is that legal? Bob's next test date: 12/10/07
I dont think anyone has asked this yet. When they cut up the sections, did the sections removed span more than 2 joists. Whenever we have to cut a floor out like that, I try to cut out over three consecutive joists.
To me it just doesnt seem as strong if the patch doesnt only spans one cavity. I also block around my patch with 2x4 for added stability.
Family.....They're always there when they need you.
I think all of the cutout sections were in one bay of the floor, so they did not span more than one joist.
That (if not blocked properly underneath) could be your problem right there.
Family.....They're always there when they need you.
Plunge cut problem areas.......sister and block with glue ....... now get back to work and GET R DONE"Gentle to the touch, exquisite to contemplate, tractable in creative hands, stronger by weight than iron, wood is, as William Penn had said,"a substance with a soul.'"Eric Sloane
You're HIRED!;)
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Not much news to report. For the past two weeks my general contractor hasn't put in more than a days work on the place, and that was just to clean up.
I took another look at the floor, and for the rooms where I'll be putting down hardwood floor, I think it should be okay. I'm going to run the hardwood perpendicular to the joists, and I'm using 3/4" T&G hardwood. I layed a few pieces over the seams as a test. The floor seemed pretty solid just with the hardwood stuck together (no nails).
I still have concerns about the area with carpet. For those areas, there is no more additional structure. One idea floated to me was to use metal plates across the seams that don't have T&G. The idea is that it would provide some more structure, but would be thinner than plywood, and would be easily absorbed by the carpet pad.
Any thoughts?
What does your contract say and why is this guy delaying work? Don't you and him talk?
I talk to his answering machine.
So, some news today. The GC came by the house and we walked over the floor. We agreed that they would lay plywood, glued and fastened, over the areas that are getting carpet.
If you're installing hardwood in some areas, and carpet in others, you really should add another 3/8"or 1/2" in the carpeted areas anyway.
Partly so that the finished levels are pretty close but also to stiffen up the floor. That should take care of everything but the unequal stair rises
I had wanted to stay away from unnecessary plywood in the carpeting areas, as I wanted to keep the possibility of eventually putting hardwood floor in those areas as well. If we do go that route, I guess we could always go with the 3/8" stuff, and the levels wouldn't be too far off.
If you screwed the plywood down, without using glue, you could still eventually install hardwood flooring.