Insulation behind shower wall

[chrissyp]

One of the walls of our new shower is on an exterior wall. There will be no plumbing on this wall. I'm pretty sure the original construction is double brick, vapour barrier, slats, and drywall. So contractor has built a 3" wall in front of the drywall to add insulation. He's planning on CBU and Kerdi membrane for the shower walls. My question is about the insulation... should he remove the drywall? From the outside in, should it go double-brick, vapour-barrier, unfaced insulation, then CBU (back of shower wall)? Or is it okay to leave the drywall and just add some insulation between the old drywall and the CBU? Any advice would be appreciated.

 

[Reach4]

The insulation of choice would be a foam board, and the edges should be filled with expanding foam. Look for posts that mention XPS.

In a colder area like Toronto, the vapor barrier goes inside of the insulation. In a hot area, it is the other way.

 

[Sponsor]

 

[chrissyp]

Thanks. If I vapour barrier the inside, I would be worried about the "moisture sandwich" between that and the Kerdi membrane. I was guessing it would be less of a concern if it were on the other side of the insulation? Would it be better to just leave the drywall up and have it go brick-vapor barrier/slats-old drywall-insulation-CBU?

 

[Reach4]

Thanks. If I vapour barrier the inside, I would be worried about the "moisture sandwich" between that and the Kerdi membrane. I was guessing it would be less of a concern if it were on the other side of the insulation?

The Kerdi membrane would be inside. With a vapor barrier at the bricks, you would have a thick sandwich, right? With the vapor barrier inside, where is the sandwich?

I don't propose to say how to build a shower.

 

[chrissyp]

I thought Kerdi advised against vapour barrier between CBU and studs. Not sure if things change by making it thicker... or if leaving the drywall up is okay? I think contractor said something about leaving the drywall because there's an air cushion on the other side of the drywall at the slats.

 

[Reach4]

I thought Kerdi advised against vapour barrier between CBU and studs.

Maybe I should say that for describing where a vapor barrier goes, inside to me means the part that is farthest from outside. Outside is where the trees and grass are.

 

[chrissyp]

Thanks again. But I'm still wondering if anybody has a firm word on whether to remove the drywall or not?