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Discussion Starter · #1 ·
My question pertains to an upcoming job. Joist spacing will be 16" OC TJI and subfloor will be 3/4" ply. Flooring is TBD but will probably be either 3/4" hardwood or ~1/2" engineered. I believe the National Wood Flooring Association recommends a glued 5/8" + 1/2" subfloor combination for a parallel application. What is the best approach when joists and flooring run parallel and squeaks are unexceptable? Do you avoid this scenario like the plague? Not a big deal? Thanks.
 

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Little more detail?

Can you give a little more detail? Sounds like you are maybe the GC and this is new construction, so I'll answer in a couple ways.

First, "no squeaks" is never a guarantee from whoever installs the floor. Squeaks are usually because of framing where a nail has missed a joist and is rubbing, loose subfloor rubbing each other, broken tongues in T&G subfloor, incorrect nails used which have backed out, etc. Squeaks usually don't come from the finished floor, but from the subfloor. Thus, screw, and maybe glue as well, rather than nail subfloor.

One of my installer handbooks doesn't discuss this specifically, just says minimum required is 3/4" plywood or OSB (no particle board). Could be two layers, could be one, whatever, as long as total thickness is at least 3/4".

If this is a remodel and you aren't doing the joists and subfloor, you may want to consider putting down a second layer of subfloor. The second layer gives it strength, turn it 90 degrees to the first subfloor. If the floor is SOLID, my bigger concern is being level. No rolls or dips, no having a joist with a noticable crown turned up, etc. May have an issue with matching the height of floors in adjacent rooms, case work, and doors.

If you are the GC, when you do the joists try running a stright edge over them and look for crowns causing "bulges," etc., before doing the subfloor. Lot of people like T&G such as Adventek on the subfloor, glued and screwed. Personally, I'm ambivalent about the glueing and the Adventek because if you ever have to take any of it up there is major pain from the glue. Makes for a really good installation, but you are saying any future problems are too bad for whoever fixes any future issues.

I'd just as soon do two layers of square edge 3/4" B/C plywood, screwed, and the second layer done at 90 degrees to the first. I'd run the first layer to the edge of your framing and set the studded wall on top of it; the second layer would be "inside" from studded wall to studded wall. If it ever has to come up hopefully it only means the top layer has to be replaced. And two layers really give a firm feel to the floor. If your floor is solid, I personally don't see any big issue with running parallel to the joists. I'm equally sure you will get a lot of differing opinions. Good luck!
 

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I agree somewhat with the last poster, squeaks come from the subfloor, save the tounges being broken during install. I just plane any high joists to keep from crowning , and I've never had a problem with the hardwood.

Screw the plywood, use good wood, no need to double up plywood to make it not squeak, just do a good job. :)
 

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Agreed

Yeah, I agree you don't have to double up the subfloor if it is a solid floor after the first layer. I'm just talking my preference if I was building a really solid house. There is a huge difference in just walking across it and feeling the difference when there is a second layer, but the cost goes up of course. The only reason I don't like Adventek is I'd rather spend a little less on the material per sheet and double the subfloor, because you are going to spend more if you double it. JCB indicated he was thinking about using two layers anyway. I suppose you could do two layers of OSB, maybe a 5/8" topped by a 1/2" layer if you were trying to save on material cost. Just depends on budget and your taste.
 

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My understanding is that 3/4 allows too much flex when run parallel to the joists & the flexing can cause squeaks with the hardwood itself.
 

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Discussion Starter · #6 ·
That's my fear (the flooring squeaking against itself if the 3/4" ply flexes too much). It seems safest to double up the subfloor as the TJIs are slightly over-spec'd for their spans and this stiffness could exacerbate the flex (or atleast how noticeable the flex is) in the subfloor. Thanks to all for the responses and if there is more input out there I'd love to hear it. At this point I'm definitely leaning toward doubling up the subfloor.
 

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Discussion Starter · #8 ·
Noises aside, support between joists is still a concern when flooring provides no additional ridgidity- especially, as I mentioned, when the joists will have virtually no deflection under foot. That said, probably guilty of some over-thinking here. Just wanted some opinions.
 

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Noises aside, support between joists is still a concern when flooring provides no additional ridgidity- especially, as I mentioned, when the joists will have virtually no deflection under foot. That said, probably guilty of some over-thinking here. Just wanted some opinions.

I've laid floors parallel to the joists with no problems on 3/4 subfloor, but my sales rep recomended I at least add 1/4" luan & make it 1" What's the width of your flooring? The wider the boards, the less of a problem it will be.
 

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I've laid floors parallel to the joists with no problems on 3/4 subfloor, but my sales rep recomended I at least add 1/4" luan & make it 1" What's the width of your flooring? The wider the boards, the less of a problem it will be.
Your sales rep is a jackass if he recommends luan under anything, especially hardwood.
 

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Strongly disagree with your rep

I've laid floors parallel to the joists with no problems on 3/4 subfloor, but my sales rep recomended I at least add 1/4" luan & make it 1" What's the width of your flooring? The wider the boards, the less of a problem it will be.
I stopped using luaun on ANYTHING about 3 years ago. Their quality control absolutely stinks. Had some jobs where the luaun (under vinyl) blew out, the last time it blew out 10 minutes after the sheet was put down. This was after we just pulled up a brand new vinyl floor (3 days old) because of the luaun blowing out. There simply isn't anything there that's going to add structural stability to the floor if you are putting hardwood over it, and may cause problems.

I'd suggest if you are willing to put down a second layer and you absolutely have to go with the minimum to save money is to use at least 3/8" OSB, but for what little cost differential is involved go to at least 3/4" OSB. If someone is putting the money into a hardwood job they shouldn't have a cow over the cost difference between luaun and 3/4" OSB, the issue would be raising the height of the subfloor. Go to B/C plywood if a few bucks isn't an issue.
 
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