Subfloor and underlayment question

[Craig D Peltier]

2nd floor of my home. Spare bath has linoleum. If I remove the floor vent I can see theres a 1/2 inch underlayment an then 3/4 subfloor.

In master bath there was carpet. I tore up carpet and pad, took out shower and pan. Where the shower drain is I can feel underside and there only seems to be a sub floor. In floor vent i can pry back one side tin an see the same thing one layer of ply.
Is this common or can I just not see it from the edges and there is indeed two layers?
I was going to cut out underlayment so my travertine, heated mat, mortar wasnt higher than carpet. But now it seems like it will be unless I remove sub floor which im not going to do. I will have to use a wood transition or metal.

Thanks

[Mike Cutler]

Craig

I don't know if it's "normal" to have only one layer of subflooring material, but I've seen it.
If you're putting down Traventine, is a single 3/4" layer of subfloor going to do it for you? and is it OSB, or actual ply?

[Walter Plummer]

One layer of subfloor under carpet is the norm around here. My son is buying his first house and the subfloor is 3/4" t&g osb. Seems strong now. Hope it ages well.

[Jason Roehl]

In the last 15 years, I've been in hundreds of new construction homes and apartment units. Pretty much all I've ever seen is 3/4" T&G OSB for a subfloor--even in the pricier homes. If an area is getting vinyl, it will get 1/4" lauan on top.

[Craig D Peltier]

Craig

I don't know if it's "normal" to have only one layer of subflooring material, but I've seen it.
If you're putting down Traventine, is a single 3/4" layer of subfloor going to do it for you? and is it OSB, or actual ply?

Its actual ply, not OSB or particle. If theres any flex in floor tiler is going to put down a rubber membrane to prevent any cracking.

Thanks for the help.

[Scott Francis]

You want a minimum of two layers under any natural stone. The membrane (Schluter Ditra i imagine) will help some but not sure you want to chance it. You also want to check (if open below) the largest unsupported span of your joists, shouldn't be more than about 10ft if on 16" centers.
If you do it properly and lay another layer of ply you want to be careful how you lay the 2nd layer. Lay the 2nd layer perpendicular to the first layer (NO GLUE!). You also want to make sure you only screw the 2nd layer into the 1st layer and not into the joists. You can find a perfect description and the reasons for doing so at

http://www.johnbridge.com/vbulletin/...rtine+subfloor

Lots of good people over there so don't be afraid to ask questions.

Good luck with the project!

[Doug Carpenter]

you definately want 1 1/4" minimum subfloor thickness for a tile floor on a wood suspension floor.

If you are doing travertine a nice marble sill that matches the color is the way to go. It will sit a 1/4" higher than your tile and should sit right under the door when it is closed.

A 3/4" subfloor is the standard thickness these days. For carpet anyway. You add to it accornimg to thr flooring.

[scott vroom]

Craig, I agree with Scott's suggestion to go to the John Bridge Tile Forum to get professional guidance. They'll guide you to a deflection table, which is what you need to determine how thick your subfloor needs to be (based on floor joist dimension, joist spacing, and max unsupported joist span). You'll also need to lay a tiling substrate over your subfloor, either a thinset reinforced membrane such as Ditra, or 3x5 concrete backer boards thinseted and screwed to the subfloor (NOT to the joists!). It's not necessary to overlay a second sheet of plywood or OSB subfloor unless the deflection table indicates your current subfloor is not thick enough.

Good luck

[Glen Butler]

Being a home builder by trade I feel I can chime in, and hopefully dispell if any myths.

3/4 OSB subfloor (homes ~20 years ago used plywood) is typically the final step before flooring. Carpet lays right over it as well as wood flooring. The vinyl has the particle underlayment for a couple of reasons: OSB is not smooth enough to lay vinyl on, and the particle board helps build up the thickness to make it more even with the top of the neighboring carpet.

Tile can be done two ways. Lathe and gray coat, or fiber rock. I prefer fiber rock, because it is easier to match wood floor and carpet. Fiber rock with a scratch of thinset under it is more than stiff enough to support the tile on a suspended floor. An anti-crack membrane will not help you much on wood, it is mainly for concrete where a crack will transfer straight through the tile.

The question is: how thick is the heated mat and how old is the carpet? New carpet is between 3/4 and 1" thick. If the carpet is old and the pad is worn out it can easily get half that.

The heated mats I know of take the place of fiber rock. You lay down thinset, roll out the mat, lay down more thinset, and then tile. Your final result will be 3/4"; the same as if you used fiber rock.