Shower install on outside double wall construction
I'm about to tear out and replace a badly installed and badly leaking shower. My intent is to do it right - do it once. I have two specific question areas I want to address. The first has to do with the outside wall which is double wall construction - the second question has to do with mating the tiled walls to an acrylic shower pan.
Right - on to the first question... My home has been constructed using double wall construction. The outside wall is 2x10, and the inside wall is 2x4. The sheathing and moisture barrier (6mil plastic) is sandwiched between these two walls. Both walls are insulated. So - in order from outside to inside, we have a) wood siding, b) insulation & 2x10 studs, c) 1/2" OSB, d) 6 mil plastic, e) insulation and 2x4 studs, f) drywall. The shower is installed against this double wall. What would be the proper order of materials from that inside wall? I think an additional vapour barrier would be a bad idea as there is already one sandwiched between the double wall. Do I put cement board only onto the studs and tile on top of that?
My second question is about mating the tile to the acrylic shower pan. I intend to use cement board on the walls, and then tile on top of that (unless I'm told differently). Should the cement board run down to the top of the flange on the shower pan, keeping the surface flush with the inside of the pan, or should the cement board drop down inside the pan, over the top of the flange? Either way, the tile comes down inside the pan and would be caulked along the bottom where it meets the acrylic. Correct?