I am redoing a bathroom. I have all ripped out down to studs. There is a window in the shower area that was shortened up so that it minimized shower spray on it. I know windows in the shower are bad idea but the window is going to stay. The original window was 3 1/2 ft x 2 ft wide. It was shortened to 1 1/2 x 2 ft wide. In the area that the area that was closed up due to the shortening of the window, dow super tough r was used for the external sheathing. on top of this is lap siding. on the rest of the wall is some other type sheathing that was used in the orginal construction back in the 1960s . It is very "breatheable". The dow board is not. This external wall is going to be part of my tub surround. I live in PA so there is a requirement for a vapor barrier on all exterior walls.

I am to the point of determining how I want to waterproof my shower walls. Kerdi is not an option since it seems more difficult than the others. I plan on either using hydroban over cement board or the standard poly behind the cement board.

My questions are as follows:

1) would the dow super tough R create a moisture problem if I used either of these 2 methods to waterproof the shower. (The area of the dowboard is 2 x 2 1/2 ft.) I am afraid that the poly behind the cement board will create a vapor problem in this area.


2) would using hydrdoban cause the same issue?

3) is a vapor barrier needed if using hydroban? The shower is not a steam shower.

Any help is greatly appreciated.