We are renovating an existing master bathroom on the second story and have a number of questions regarding how to best proceed with the construction. Chime in with any recommendations.

Shower Details (not a steam shower)
* 48"x36" shower enclosure with a 14" void space between exterior wall and back of shower. The width of the bathroom is 62" but we needed room to enclose a vent stack along the outside wall and create some shelving so we are going with a 48" wide shower.
* Hardibacker for shower walls and ceiling
* Tiles only on walls, not on ceiling
* 6 mil poly for shower ceiling and 1 exterior wall.
* Waterproofing system - Laticrete 9235 or AquaBan?
* Cast iron shower pan - 48" x 36"
* Panasonic exhaust fan
* Opening at top of glass doors for ventilation.

1. If we use a waterproof system on the Hardibacker walls I understand we should we not use 6 mil poly behind the walls as this may trap moisture. Is this correct?

2. What about if you want to add insulation for noise reduction in an interior wall? If you should not use 6 mil poly to cover the batt insulation what other options are available?

3. What about the ceiling? Are we ok with poly behind the Hardi or is it the same as the walls in that we would create a second vapour barrier? The insulation is the loose stuff so it needs to be contained in the attic somehow without falling onto the cement board.

4. Any special paint or preparation for the shower ceiling so that it lasts (without tiling)? I know good ventilation helps. Is Hardi ok for this application?

5. For the void space between the exterior wall and the framing wall of the back of the shower, do we bother to drywall the exterior wall and interior wall in that void? Should we add in some foam insulation or insulation batts? Any potential issues that we should be aware of here since there is a large enclosed cavity?

6. Any issues with waterproofing the back of the shower wall that will be adjacent to the void space? The exterior wall with 6 mil poly will be about 10" - 14" away from the adjacent shower wall that will have the waterproofing application.
Take a look at the enclosed photo where the vent stack is at the back will be the enclosed void space. To the right of the vent stack will be the back shower wall with Hardibacker and some type of waterproofing system.
http://img168.imageshack.us/my.php?image=dsc01526bk4.jpg

Thanks,
Greg