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Discussion Starter · #1 ·
On the bathroom we're going to be tiling shortly, it has 1/2 OSB non tongue and groove.

Installing 12x24 over it. Typically we use ditra but we might be using Duroc on this project because of a curbless shower. Still trying to figure out the details there...

So I need to level the floor, it's pretty bad in some places. I also need to add some sort of plywood over the osb to meet deflection ratings.

Which order should I do the SLC and plywood in? I'm assuming plywood first then SLC. Is 1/2 underlayment grade plywood sufficient as long as the seams are offset from the current seams on osb without doing additional blocking since osb is non T&G?

If I do Duroc instead of ditra, does the SLC need to go over the Duroc instead of attaching Duroc through the SLC?

Thanks
 

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Discussion Starter · #3 ·
The 1/2 osb is the subfloor. non T&G. floor we ripped out was a metal lathe mud job.
Obviously I need to add an underlayment quality plywood over the osb and then I will use ditra, duroc, or now I'm looking at this green skin stuff... looks awesome (anybody have input on that?)
It's for tile, not lino.

I guess I'm having a hard time figuring out what thickness plywood I would need to use and since the subfloor isn't T&G not sure of how to handle that aspect.
 

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Discussion Starter · #5 ·
If it helps, it's on the first floor with crawl access so I was thinking that I could do blocking at the joints if that would solve the non-T&G problem. After doing that, what thickness plywood should be used?
 

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That floor must feel like a trampoline. Are you sure it's only 1/2 OSB?
 

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My understanding is that 1/2" (of anything) as your bottom layer is basically worthless.

You can either pretend it's not there and install a proper subfloor (3/4" T&G) over it or remove it so it's not there and install a proper subfloor in it's place.
 

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Discussion Starter · #8 ·
Inner10 said:
That floor must feel like a trampoline. Are you sure it's only 1/2 OSB?
It does... Lol. I'll confirm today. Around here we seem to get 3/4 T&G or 1/2 non-T&G. Thankfully more 3/4 on our jobs
 

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My understanding is that 1/2" (of anything) as your bottom layer is basically worthless.

You can either pretend it's not there and install a proper subfloor (3/4" T&G) over it or remove it so it's not there and install a proper subfloor in it's place.
If you remove it, you could sister joists while leveling. 2b1s.
 

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Discussion Starter · #11 ·
On the plus side the joists are 2x8 spanning 7'. I have a deflection rating over L/1000. Why you throw non-T&G over that is just silly.
 

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On the plus side the joists are 2x8 spanning 7'. I have a deflection rating over L/1000. Why you throw non-T&G over that is just silly.
I would either pull the OSB and lay 3/4" T&G or go 1/2" on top of the OSB overlapping the joints.
 

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Discussion Starter · #13 ·
TNTSERVICES said:
I would either pull the OSB and lay 3/4" T&G or go 1/2" on top of the OSB overlapping the joints.
We decided to pull the OSB and do 3/4 T&G.

When sistering joists to create a flat/level floor, what size do they have to be and can you notch for plumbing and electrical etc?

I have 2x8's, 7' long as the joist structure.
 

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We decided to pull the OSB and do 3/4 T&G.

When sistering joists to create a flat/level floor, what size do they have to be and can you notch for plumbing and electrical etc?

I have 2x8's, 7' long as the joist structure.
2x6 glued and screwed. Notch as needed.
 

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Discussion Starter · #15 ·
TNTSERVICES said:
2x6 glued and screwed. Notch as needed.
Thanks Rob. To further my education, if for example it was 2x10's spanning 12 feet and the joists still met the deflection requirement, could you still use a 2x6?

I guess the question is, what dictates the sistered size if the original is structurally sound?
 

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Thanks Rob. To further my education, if for example it was 2x10's spanning 12 feet and the joists still met the deflection requirement, could you still use a 2x6?

I guess the question is, what dictates the sistered size if the original is structurally sound?
I'll probably get flamed for this, but I always go a size down when structurally sound to level a floor. Technically you should match the size, but I think it's overkill for leveling purposes. I just glue and screw the crap out of it.
 

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I'll probably get flamed for this, but I always go a size down when structurally sound to level a floor. Technically you should match the size, but I think it's overkill for leveling purposes. I just glue and screw the crap out of it.
hack...:jester:


I have done the same especially on older homes with lathe ceiling below or notched in brick pockets etc...2x8 gets 2x6 etc.....
 

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Glad you ripped out the 1/2". Being it wasn't T&G, you did the right thing.

Going directly over it with new T&G just seems like a waste of height. No need on having a subfloor 1 1/4" thick when you have such a good deflection ratio to begin with.
 

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Discussion Starter · #19 ·
Ya know, when I was ignorant on this stuff... tile laying was easy. It's harder now...:laughing:

I'd much rather be doing it right though.

So to complicate things with the height issue, the master bedroom has the 1/2 non-T&G with a 3/4 underlayment for carpet. Some sort of mdf or pressed board or something.

After I switch my subfloor to 3/4 and leveling it out which might raise it some, I will be anywhere from 1/4" above the subfloor to even with the underlayment. I really won't know till I rip everything up and level the joist and install 3/4".

Ideally I want the finished tile surface to line up as close to flush with the carpet as possible. For the sake of getting input now, I see my potential options for going over the subfloor being, ditra, 1/4" or 1/2" hardie, or green skin, which would give me a range of heights to work with and get a great finished result related to the carpet.

Is this the type of stuff you guys do on every job? In the past it's just been, demo old floor, clean subfloor, put down ditra, tile, and you're done. A transition strip makes up for the height difference and never had complaints about it. I know it's a bit of a ramble, just never gone this deep into floor prep and considering finished heights.

It's also a barrier free shower cause they have a friend in a wheel chair and it inspired them to make this whole project more handicap friendly, wider doorways, etc. Yet another reason to have as little height difference as possible.
 

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Discussion Starter · #20 ·
One more thing... I was just on the phone with dad explaining all this and he thought it sounded good... till I mentioned the sistering with 2x6. He had thought 2x4's would be fine since the joists were ok. Can someone explain why we should use something larger than 2x4's?
 
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