New construction with wood sub floor

[bKelly]

First off, new member here…

We are in the process of having a house built. I have a contractor putting the house “in the dry” and I am finishing the job to save money.

My wife wants tile in all the rooms except the bedrooms and living room.

The joists are 2x8 and 16”oc. The sub floor will be 5/8” plywood.



What do I need to do to install 12” ceramic tile on this floor?

[bbcamp]

Hi, Kelly!

First off, you need to ensure that none of the floor joist spans are longer than 11 feet. If they are, you need to increase the depth or thickness of the joists, or add a beam to reduce the span.

Second, 5/8" is the very thinnest subfloor that can be tiled. We recommend 3/4" or more. Now would be a great time to upgrade the subfloor! It can be handled later, but the fixes would be less satisfactory than getting it right the first time. Be sure that he uses exterior rated plywood.

When you get ready for tile, you will need to add an underlayment to the tiled areas. This can be either cement backerboard or a decoupling membrane, the choice being based on cost, ease of installation, floor height differences, etc.

I don’t think any of the spans will be over 11 feet.

So the plywood needs to be exterior grade if I even use a concrete backer board?

The lumber is already purchased so I am stuck with the 5/8” thick sub floor…

Do I need to add another layer of plywood and then the backer?


Bobby

[bKelly]

That is my post above...

for some reason I wasnt logged in when I posted

[bbcamp]

That's OK Bobby, I'll talk to anybody!

Yes, the top layer of plywood needs to be exterior rated. You will be bedding the backerboard in thinset as you set it. The bottom layer need to be exterior rated if it is over unfinished crawlspace.

I would add 3/8" (preferrably 1/2") plywood over what you (will) have now. When you install the second layer, remember to off set the edges about 4 inches from the joists and about a 1/2 sheet from the joints in the bottom layer. Screw the plywood down 4 to 6 inches along the edges and 6 to 8 inches in the field, and avoid screwing into the joists. This second layer needs to be de-coupled from the framing movement. On top of this, add 1/4" backerboard or Ditra, a decoupling membrane from Schluter company.

[bKelly]

I was planning to add at least a ½” ply over the entire sub floor anyway…



Ditra is new to me…

How is it applied? I assume it is a rolled product that is put down with thinset?

What are the advantages over backer board? Is it easier/faster to lay down than the bb?

[bbcamp]

You have the gist of it. www.schluter.com for details.

[bKelly]

Ok I like the looks of this product.

Do you recommend it over concrete backer?

[jadnashua]

You generally use Ditra in place of CBU.

[bKelly]

I don’t guess I made myself clear… sorry

I meant to say, do you recommend Ditra instead of CBB.

[cx]

Ditra is thinner, easier to install, more expensive.

CBU is thicker, more work to install, much less expensive.

Either will be suitable in your situation, especially with the additional plywood.

My opinion; worth price charged.