Minimum Underlayment Requirements

jreiner13

When installing 16 inch ceramic tile, what is the minimum underlayment requirement. I have 3/4 in subfloor over 16 in on center joists. Can I put 1/4 hardibacker down and go? Or do I need additional layers of plywood? Thanx.

angus242

What size are the joists and what unsupported span to they have. How old is the house? It the subfloor OSB or ply?

Some advice....instead of thinking about "minimum", think about "best".

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jreiner13

They are 2x8s on about a 6 foot span. The subfloor is plywood, and I stressed minimum meaning minimum height build up. The tile is against carpet, and I dont want to put a big toe stubber in there.

jreiner13

Angus,
You ever work with Ditra? Would that be an acceptable option to keep my height to a minimum? Thanx.

angus242

Are you sure...6'? That is an odd length.

If that is the case, the deflection is ok. However, there is another kind of deflection; the subfloor between the joists. That is why I like to add at least 1/2" EGP, then Ditra.

It is a peeve of mine when floor height is mentioned when talking about tiling. That should be one of the last concerns, not first. No offense to you specifically.

I don't think the 1/2"/Ditra/tile combo is all that tall anyway. It's a smidge more than if your carpet butted to hardwood.

But to answer your question, 1/4" CBU is fine as and underlayment.

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Angus
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"Promise only what you can deliver. Then deliver more than you promise"

angus242

Yes, I use it all the time. Good stuff

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"Promise only what you can deliver. Then deliver more than you promise"

PrecisionFloors

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JazMan

Hey jreiner13,

I agree with Angus, that's my biggest peeve too! You want the floors to be the same height? Then install the same floors in all rooms. Carpet sucks anyway. It's not sanitary and makes you and especially young one sick. Carpet is cheap to start, but over a 20-30 year cycle, ceramic is much cheaper to own.

I disagree with Angus about how much subfloor/underlayment thickness is required though. Although the more the better... a 3/4" subfloor is plenty stiff enough for ceramic in your case.

And Ditra......Best product in our industry next to Kerdi Membrane and Kerdi Drain.

Jaz

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angus242

Carpet does suck!

As for adding to subfloor, it's hard to cover everything about tiling in a simple post. My point was to get jreiner, a carpenter, to think about a stiff floor, not a minimum required floor. I know in my house, I have 3/4" T&G and it's only 5 years old. I have a few spots where the subfloor is squishy. I would definitely not tile over those spots without adding something to stiffen it up.

I asked how old the house was. I guess I could have mentioned to check to make sure the ply is completely sound. Adding 1/2" EGP may not be a requirement but it absolutely won't hurt anything.

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Angus
L+M+O+P=C
"Promise only what you can deliver. Then deliver more than you promise"

JazMan

You're absolutely right Angus, it won't hurt anything and the more the better of course. It's just that many CBU and membrane manufacturers say you can apply their products over 5/8" sub. , and when we poo-poo that, some people think we're going over board.

A properly installed 3/4" sub is a good base for tile, the key word is "properly? For example if your own floor is squishy in one spot, it is obviously not installed properly. But maybe a few screws would fix that.

Anyway, you do not pick a method to arrive at the height you want. You chose the proper method, then deal with the transition as necessary.

Jaz

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angus242

Absolutely agreed

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Angus
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"Promise only what you can deliver. Then deliver more than you promise"

neolitic

Gee, civility.
Something to get used to?

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jarvis design

Whats next....tea and crumpets??

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