Subfloor suggestions

Blueking · 01-14-2013, 12:21 PM

Hi everyone,

I am hoping to get some advice on the proper subfloor and underlayment for my heated tile bathroom project.

Bathroom is about 10 x 5 ft with 24" OC open web trusses that span the whole house (approximately 20'). The curent subfloor is 23/32 plywood. We are planning to put down a porcelain tile and a heated mat systemf.

I have seen a lot of different recommendations for subfloor/underlayment combos and was hoping to get some clarification. Ultimately want to have the thinnnest subfloor for an easy transition to the carpet in our bedroom (1/2 pad plus carpet).

What questions boil down to what is the thinnest subfloor that will still be suitable for tiling? Also is there a subfloor that is better for retaining the heat of the heating mats?

Thanks,
Brian

JazMan · 01-14-2013, 05:36 PM

Welcome Brian,

If the subfloor is installed correctly and is in perfect condition, you can use Ditra XL over single 3/4" ply or OSB on joists spaced 24" o.c. (is the subfloor spaced between sheets?). Ditra XL raises the floor 5/16", with normal tile makes the total about 3/4".

But you could decided to install a plywood underlayment to add strength, then use regular Ditra and shim the carpet a little instead. We usually want the tiled area to be higher and often use a marble threshold in the doorway. Many ways to do it.

Personally a single 3/4" over a 24" span scares me. But the book says it'll work per above, but everything better be done right.

Jaz

Blueking · 01-15-2013, 02:13 AM

Thanks for the quick response.

I had the same concerns about using only the Ditra-XL and the Ditra-XL is also hard to find in my area so I think I will go with the additional plywood underlayment layer followed by regualr Ditra.

A few additional questions for you then, how thick of plywood underlayment would you recommend to go on top of the current 23/32 subfloor? Would it be possible to add think enough plywood (ie another 3/4) that I would not need the Ditra or do they protect against different types of movement?

Also would it be acceptable to leave my current sheet vinyl down and just screw the plywood over it or is it required to remove it?

Thanks again,
Brian

joecaption · 01-15-2013, 10:06 AM

Are you 100% sure there's not a layer of 1/4 under that linolium?

Blueking · 01-15-2013, 11:04 AM

After further investigation Joecaption is correct, there is a 1/4 layer of plywood between the sheet vinyl and the 23/32 subfloor.

JazMan · 01-15-2013, 03:00 PM

Quote:

After further investigation Joecaption is correct, there is a 1/4 layer of plywood between the sheet vinyl and the 23/32 subfloor.

Well of course there is, resilient flooring is not installed directly on the subfloor.

So, removed the 1/4" with the flooring still attached in one operation. Prep the old subfloor and install the thickest underlayment you can stand, but no thinner than 3/8". I recommend 1/2" or 5/8". Be sure it's not cheapo CDX sheathing ply, you want B/C underlayment grade with exterior glue bonded plies.

Then the heat mats, self leveling and then Ditra and tiles. What kind of tiles are you planning?

Jaz

Blueking · 01-16-2013, 01:06 AM

Planning on doing a 12 x 12 porcelain tile.

jeffnc · 01-16-2013, 08:05 AM

Quote:

Originally Posted by Blueking

A few additional questions for you then, how thick of plywood underlayment would you recommend to go on top of the current 23/32 subfloor? Would it be possible to add think enough plywood (ie another 3/4) that I would not need the Ditra or do they protect against different types of movement?

They protect against different types of movement. In fact if given the choice between spongy subfloor with Ditra on top, or solid subfloor with no Ditra on top, I'd choose the latter. But hopefully using a little of both will be acceptable to you in terms of height transition to your carpet.