Subfloor thickness for tile

[lowthreeohz]

Got a question I'm hoping some of you construction guys can help me figure out.

I have 7/16" OSB decking on the second story of my house. Joists are 2x10 on 16" centers. I'm putting tile floor in (bathroom, ~100 sq ft) and not sure how much (if any) plywood I need to put on top of the OSB to support the load. Some have said put some 3/8" ply up, others said just 3/8" or 1/2" wonderboard and call it good. Not sure which I believe, and don't want to bank on suppositions.

I have 3/4" off the OSB to be flush with the hardwood, would be okay with a slight difference at the threshold.

TIA

[black2002ls]

we use 3/4 tongue and groove for all of our second floor decking and tile over a membrane on top of that. We use I-joists under all of our upstairs living space, so I can't comment on the joist spacing. if you have 7/16 up there, you should be able to get by with 1/4 or 3/8 and change the orientation. Lay the new stuff so that the seams run perpendicular to the flooring that is there. Then us some kerdi or foam membrane underneath the tile to help prevent cracking.

[GeorgeG.]

If you're going to add anything, I would add hardiboard/wonderboard vs. another layer of plywood.

In one of my old houses we had this raised subfloor that was our entry way that lead to two steps down into the living room on each side...it had plywood (don't remember the thickness now). I added 1/4" hardiboard and that floor did not budge at all when I bounced on it.

If the current plywood is not soft, I'd layer it with hardiboard and tile it. For some reason, I'm not a fan of the wonder board.

Hope that helps.

[lowthreeohz]

Thank you both, that's the kind of info I was looking for.

George, you mention using Hardi or wonder board then later say you don't like wonder board. Care to elaborate on why you prefer hardi?

Again, thanks guys.

[8mpg]

Id definintly add a layer of hardiboard or something that is designed for a tile underlayment. Dont forget to damp it before you put your tile down so the board doesnt try and soak up all the water from the thinset.

Most houses use 3/4" subfloor or more. Advantech sheeting is 1" or 1 1/8" which is preferred to 7/16" osb.

[lowthreeohz]

Copy that, thanks dude.

[Mysticcobrakilla]

I ain't laying tile upstairs without hardibacker or the like. Add some red guard and your good to go.

[GeorgeG.]

No particular reason. I'm sure that's what the HD guy steered me to or maybe the Wonder board wasn't out yet. I used a hand scorer to cut it with pretty good success...I guess I didn't own a circular saw at the time. I also liked how it had straight edges and just looked like a cleaner install.

I haven't used wonder board though. It just seems like it's a little harder to work with. I only mentioned wonder board as another option over plywood.

If it's any testament, my wife had a home daycare at the time so the floor saw a lot of traffic by some large parents too and I never had any issues with popped grout or tiles. Just be sure to screw it down with the recommended screws at all screw points.

[lowthreeohz]

No particular reason. I'm sure that's what the HD guy steered me to or maybe the Wonder board wasn't out yet. I used a hand scorer to cut it with pretty good success...I guess I didn't own a circular saw at the time. I also liked how it had straight edges and just looked like a cleaner install.

I haven't used wonder board though. It just seems like it's a little harder to work with. I only mentioned wonder board as another option over plywood.

If it's any testament, my wife had a home daycare at the time so the floor saw a lot of traffic by some large parents too and I never had any issues with popped grout or tiles. Just be sure to screw it down with the recommended screws at all screw points.

Thanks again. After your initial post about the two I did some googling and saw that many people share your sentiment on the wonder vs hardi. I'm going to return the 4 sheets of wonderboard that I got and get some hariboard instead. we need to pick a tub, tile, vanity, toilet, etc out this weekend so i'll have plenty of opportunity to swap it out for the right stuff.

I popped a couple of holes in the subfloor with my nail bar while I was pulling up the 19/32, so yesterday I floated a small layer of patch over everything that was damaged and surprisingly I have very little deviation in floor height. my one small victory so far from this whole bathroom fiasco.

[GeorgeG.]

So how's it looking? Did you start this project yet?

[lowthreeohz]

Yeah, its slowly coming along. I decided to toss everything and start fresh. I ended up adding some plywood on the osb then used 1/4 hardi on top for the tile. The new tub was a bitch to get in as a) the builders didn't give a fuck about dimensions because it was a fiberglass tub/shower insert or b) things shifted enough over time where it was necessary to notch the studs a rch before I could slide the tub into place. Put a new shower valve and all that stuff, replaced the lines, now and the walls are back up and waiting for tile. Been spending entirely too much time riding the motorcycle or kayaking lately so progress has slowed. We have 2 other bathrooms so there's no real sense of urgency on my end, much to the annoyance of my girlfriend