subflooring

Been kicking this around for weeks not really sure what to do kitchen& utility room is 250sqft, the subfloor 5/8 ply, the floor joist are 2x8 @16oc for must part they span 9 1/2 ft except in the hall were it 11ft but there doubled up there. The problem is the tile will butt up agaist 3/8 hardwood I"m worried about the hieght of the transtion. Should put 1/2ply down and use 1/4cmu or ditra. Or 3/8 ply and use ditra or 1/4cmu. What do you guys think. One other thing should I seal the ply with anything pior to thinsetting my board down. Your advice would be greatly aprecated, louis

If your concerned about the extra height; my advice is to use ditra because it's only 1/8" thick.

"should I seal the ply with anything pior to thinsetting my board down." Not a good idea as the sealer will seal the pores in the plywood causing the thinset to fail.

I have a couple questions;

1. Which part of the house are you planning to tile?

2. What type of tile are you using ceramic or natural stone? The reason I ask is I calcaluted the rate of deflection for your floor and for a span of (9.5)' it's L/544 which is good for ceramic but not for marable or granite as it needs to be at least L/720.

Hi Lou,

It is always best to install as thick an underlayment as practical when installing tile floors. I guess your 3/8" engineered wood is glued right on the 5/8" subfloor. Wow, that's thin for both items.

A height difference of up to an inch is easily workable. Just fashion a threshold in the doorway, it can even be set as a ramp.

So, because of your 5/8" subfloor, I recommend installing 1/2" underlayment grade plywood and then Ditra. Ditra is a premium product and method.

With the above method your tiled floor will be about 5/8" higher than the wood side. No problem.

Jaz

Hey guys thanks for getting back as quick as yous did, to answer Nates question the rooms are 1st floor adjoin kitchen and laungry room and I"m going with ceramic. If I install the 1/2 a/c or b/c rated ply I read where I should not screw them down to the joist,& should run the ply the opposite direction of the 5/8ply that down already thanks Lou

Well, 1 for two isn't bad, but this is not baseball.

You are correct that the underlayment is fastened only to the subfloor and not the joists too. Use 1 1/4" screws and all will be fine. Who told you about turning the plywood the other way?

The underlayment is installed across the joists just like the subfloor. Just offset the new plywood from the the sub both ways. Be sure to leave an 1/8" gap between sheets and about 1/4" around the perimeter and any other vertical obstructions. If possible place an end seam at 1/4 distance of the joists spacing. In other words, with 16" O. C., the end seam should be about 4" from a joists. This gives the plywood maximum strength and is less influenced by joists movement.

Jaz

Thanks lou

Deflectionwise your good to go for ceramic.

As Jazman has already stated the second layer shouldn't be fastened to the floor-joists and is ran perpendular to the first layer so the panels are more staggered, but it's also a good idea to stagger all your seams for the second layer so they don't line up
With the first layer.

Thank you Lou

Nate,

That is NOT what I said. The underlayment is installed parallel NOT perpendicular to the subfloor, and of course off-set BOTH ways.

Jaz