bathroombathtubshowertilewaterproofing
We are in the process of doing a bathroom remodel and we noticed that the bathtub we ordered does not have a flange. The bathtub will be installed in an alcove setup (surrounded by 3 walls) and will mainly be used as a shower.
The bathroom is currently stripped to the studs, the floor is not finished (just leveled).
What is best practice to install this sort of flange"less" bathtub?
We have already purchased 1/2in Durock and stone tile that will be used in the bathroom walls around the bathtub.
The flange should sit on top of the finished floor, if it doesn't you'll have to modify the plumbing or find another way to achieve this.
Notice in this image how the toilet waste pipe sits just inside the flange opening, this is the proper way for a toilet to sit on a flange. Even without a wax ring, this union is not likely to leak under normal circumstances (I'm not recommending a wax ring not be used).
Some folks recommend using a thicker wax ring, or even doubling up wax rings. The problem with this, is that you end up with a waste pipe made from wax. Now this might hold up, but more than likely it's eventually going to fail, and leak.
If you have access to the flange from below, you might be able to modify the plumbing to make the flange sit atop the floor. In most cases, however, this is not an option.
There are adapters available, that solve this exact problem. The Set-Rite Toilet Flange Extender Kit; described in the answers to this question, Comes with different size spacers, which allows it to compensate for various sized offsets.
You should only place a vapor barrier on the exterior side of the exterior wall, allowing the assembly to dry back to the inside if water does get in past the tub surround. I would recommend paperless drywall over cement board for the tub surround, as well -- gypsum board of all types is vapor open (around 50 perms) while serving as an air barrier, allowing drying to the inside without letting a ton of humid air into the wall cavity, while cement board is a fairly severe vapor retarder at 4-8 perms, which puts more pressure on the ability of your tub surround to keep water out of the wall to begin with.
When you stick a vapor barrier on the inside of a building, all will seem well at first, until you go and turn the air conditioner on. Then, the moisture in the warm, humid outside air that fills the wall cavity will start to condense on the cold exterior surface of the vapor barrier (assuming an insulated assembly), and you get mold as a result.
A similar problem will happen if you try to insert two vapor barriers in the same assembly -- the inside one will still generate condensation despite the efforts of the outside one to keep all that humidity at bay, and now there's utterly nowhere for the moisture to go!
Of course, there's no point in putting a vapor barrier on an interior wall -- the airspace of a partition should never communicate with that of an outside wall!
More info on why vapor barriers are like badgers can be found in BSI-073, aka "Macbeth Does Vapor Barriers."
One other mistake that can be made in a modern, tight house is to slap a "fart fan" in the bathroom and call bathroom ventilation done. Doing that just means that your makeup air will come from all sorts of random leaks that have no business providing indoor air to people -- especially if one of them happens to be the range hood, or the exhaust of some appliance.
The easiest way to solve this problem is to provide transfer air to the bathroom from a zone that's being blown on, say the basement, if your basement is a suitable transfer air supply, as not all are! (You'll need to provide, oh, 10% extra makeup air as this is a transfer air setup, as well.)
Of course, if the OP's house leaks more air than a SR-71 on the ground leaks JP-7, an old-fashioned bathroom exhaust fan like the one the OP proposes will serve him fine.
More on ventilation in general can be found in BSI-070, "First Deal with the Manure and Then Don't Suck", by the way.
Best Answer
I was and still am in complete agreement with paperstreet's answer, buy another tub. I've never used this system. These look like a fail waiting to happen. Available from schluter.com, asked about at johnbridge.com calling them field installed flanges.