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Old 10-31-2011, 03:48 PM   #1
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Subflooring sagging need your help


Hi all, I bought a house that had a converted garage. When I bought the home I was well aware that the floor in this room sagged and the guy did a half a$s job of doing the addition. He raised the entire bed and bath with 2x6's off the concrete, which I assume was done for plumbing reasons.

Anyway I was demoing the tile today to put down concrete board and replace the tile when I think I found the problem with the sagging floors, 1/2" plywood was used as the subfloor. I'm not sure what the spacing is on the joists as I just started to get into this but my question is whats the best way to fix this issue? Should I glue and screw 1/2" over the flooring? What about the areas that are already sagging? Do I replace the entire thing? I really appreciate you're help


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Old 10-31-2011, 03:54 PM   #2
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Subflooring sagging need your help


How far apart are they spaced and what is the length of their span?
I believe 5/8" is minimum thickness for subfloor of a tile job (not including concrete backer board or Ditra).
If span is ok for the 2x8s, then I'd go at least 5/8" or better 3/4". Finished floor height to adjoining rooms may become an issue.

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Old 10-31-2011, 04:01 PM   #3
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Subflooring sagging need your help


Ok at least in the bathroom the joists are 16" apart. He used 2x6s with a span of 8 feet in the bath and 12 in the bedroom. For the tile bathroom what should I do to stablize the floor before putting the concrete board down? For the bedroom, which will have plastic wood, what should I do about the considerable sagging in there? Right now there is carpet down and I haven't even looked at it but I'm assuming it has 2x6s running 12 feet with 1/2 ply on top. I am looking for the cheapest but best solution.
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Old 10-31-2011, 04:19 PM   #4
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Subflooring sagging need your help


What is below the 2X6's?

There is no way a 2X6 structure will span 12 feet without some pretty good bounce. Assuming I'm reading your information correctly.

A subfloor of 1/2" thickness is not up to code but really would not necessarily have a great effect on overall bounce of unitized 2X6's. Half inch plywood would serve more to cause plenty of deflection between the joists.

Do the floor joists have cross bracing between the joists?
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Old 10-31-2011, 05:11 PM   #5
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Subflooring sagging need your help


Concrete underneath, guy raised the floor so he wouldn't have to dig in the cement for the plumbing. There are no bracers, the guy didn't even nail this thing in right. Might have been a screw every 8 to 10 on the plywood. What to do? I think the 2x6s should be fine since it's got the cement slab underneath it right?
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Old 10-31-2011, 05:27 PM   #6
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Subflooring sagging need your help


Okay let's try this another way.

Are the 2X6's over concrete sitting firmly on the concrete? If not, how much gap is there?

Quote:
I think the 2x6s should be fine since it's got the cement slab underneath it right?
Not necessarily.
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Old 10-31-2011, 05:36 PM   #7
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Yes they are firm against the ground.
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Old 10-31-2011, 05:42 PM   #8
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Quote:
Yes they are firm against the ground.
Okaaaaya! Then how is it they are sagging or bouncing or whatever it is they are doing that you find offensive?

What about the bedroom - same deal?
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Old 10-31-2011, 05:53 PM   #9
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Okaaaaya! Then how is it they are sagging or bouncing or whatever it is they are doing that you find offensive?

What about the bedroom - same deal?
Yeah they are sagging in the bedroom as well. I'm assuming it's because 1/2" plywood was used. So I'm looking for a way to fix it.
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Old 10-31-2011, 05:55 PM   #10
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I think I'm totally lost and without explanation at this point. I'm gonna pass for now.
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Old 10-31-2011, 07:02 PM   #11
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Subflooring sagging need your help


Ok sorry if I'm all over the place. Let me try it again.

Bathroom and bedroom floors are 1/2" plywood on 2x6 beams which the beams rest on a concrete slab. Both the bathroom and bedroom have sags in the floor and bounce when walking on floor. I am looking for the best way to resolve this.

Thanks for your help.
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Old 10-31-2011, 07:44 PM   #12
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Subflooring sagging need your help


I'm going to assume you mean sag and bouce 'between' the joists.

With 1/2" plywood on 16" OC...I can see that.

Did he use pressure treated wood for the joists? 'Technically', anything that touches the concrete need to be PT.

Solution? Anything you do cheap is going to end up half assed....but it does not mean you have to break the bank.

I think your minimum floor sheathing would be 3/4" T&G plywood. Personally, I would go 1 1/8" T&G. Labor to install is the same...and only costs maybe 50% more...but will be almost twice as stiff as 3/4" plywood.

You could get by with 3/4" if you added joists between the existing...but when you look at the total labor and material for either option...the 1 1/8" T&G will be cheaper overall.

Make sure you have blocking in the middle of those floor joists so they don't try to roll over on you. I believe the typical standard is if the span is over 8', add blocking.
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Old 10-31-2011, 08:07 PM   #13
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Subflooring sagging need your help


Cross blocking needs to be done over 6'9" here. Probably different codes in different places of course.

I think a picture would help a lot too if you could draw up a crude on in paint or something.
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Old 10-31-2011, 08:56 PM   #14
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Originally Posted by ddawg16 View Post
I'm going to assume you mean sag and bouce 'between' the joists.

With 1/2" plywood on 16" OC...I can see that.

Did he use pressure treated wood for the joists? 'Technically', anything that touches the concrete need to be PT.

Solution? Anything you do cheap is going to end up half assed....but it does not mean you have to break the bank.

I think your minimum floor sheathing would be 3/4" T&G plywood. Personally, I would go 1 1/8" T&G. Labor to install is the same...and only costs maybe 50% more...but will be almost twice as stiff as 3/4" plywood.

You could get by with 3/4" if you added joists between the existing...but when you look at the total labor and material for either option...the 1 1/8" T&G will be cheaper overall.

Make sure you have blocking in the middle of those floor joists so they don't try to roll over on you. I believe the typical standard is if the span is over 8', add blocking.
Great advice, thanks. But if I didn't want to tear up the existing floor could I screw plywoood on top of the existing? And if so what thickness?
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Old 11-01-2011, 05:18 AM   #15
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Subflooring sagging need your help


Glue and screw 3/4 t&g plywood over what you have. The joists should have been treated or elevated slightly above the concrete. Probably not something easily remedied at this point, but not likely to be a problem.

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