Like this? Never heard of em. :-) Other than the sloping of the ceiling, the only other thing, and this one is much more important-- is that the entire room must be one giant membrane envelope, and it goes further than that-- it must be vapor proof, as well as waterproof. Most roll-on membranes (including my beloved Hydroban) require the use of an additional vapor barrier behind the cement board (either poly or tar paper), and in my way of thinking, that negates all the pluses of using a topical waterproofing. The only roll-on/ trowel-on membrane that has enough of a perm rating that it can be used alone is Hydroment's Ultraset urethane waterproofing, which is a trowel applied membrane. Hands down, the best membrane (for MY money) for a steam shower or steam room is Kerdi. In fact, I'm doing a steam shower right now and that's the membrane being used. It's even going in curbless.

Thanks for the answer Bill. The exterior wall Durock was the first piece I put up. It is about 1 1/2" inches under the right window trim, 3" under the sill, and also the trim under the sill. The Durock is screwed under the trims. Trust me, I put that trim up to stay. I could take it down but I am afraid that I will rip it apart - particularly the sill. Do the slits in the insulation have to be distributed uniformily? There is really only one significant tall chase. Maybe I could put a raiser blade on something and work my way partway up. I can definitely get to the chase under the sil without removing the Durock. I also thought of drilling a couple of small holes in the bathroom floor close to the chase, from underneath, and putting a vent in the ceiling of the basement room below. Is it correct to assume that if there is moisture in the chase, that it will not be a problem if there is air exchange? Will air move up and down the chase?

We have a steam shower. We don't have a rubber membrane all around. We did get the ceiling and walls tiled and we have the glass going all the way to the top to seal it in and a transom over the shower door, but the door is not sealed especially tight. We also made our shower surround out of corian and had a bench made out of the same material as, everyone said, sitting on granite is much colder. We put a light in under the seat as we didn't want to steam with the overhead light on...not pleasant. And we added a speaker into the bathroom so we could have music while steaming. While I use that at other times, you have to really crank the volume up as the steam itself is noisy. The only thing is, I kept telling the project manager I wanted the ceiling slanted so the condensation didn't drip on me when I was steaming. The framers said the tiler could do that, the tiler said the framers should've done that, and it didn't happen. I get a few drips, but it's not bad. Sorry, I can't help with the cost differential.

We, too, were appalled by the price of steam shower lights and were thinking about not putting one in. Our electrician said that he had a light that he swore would work in a steam shower. It was only $25 and we were skeptical, having read that steam can take the finish off fixtures and penetrate the workings of the light unless it has the proper vapor barrier. But we trusted him and told him to put it in, thinking that we weren't risking much. As you would expect given the price, it's a very plain jane light. We've only had the shower in working condition since May; that's not a very long trial. I'm loathe to recommend it, but it might be an option. It would be good to have opinions from others with real expertise, however.