Exterior shower wall insulation

[chrissyp]

Planing on a CBU and Kerdi membrane shower in a new location. One of the shower walls is on an exterior wall (no plumbing). From the outside in, I’m pretty sure it's currently double brick, tar paper/slats, and drywall. We framed for a 3″ wall in front of the drywall to add some insulation. Question is, should we remove the old drywall or is it okay to just leave it and add unfaced insulation between the old drywall and the CBU?

 

[chrissyp]

Sorry, I double posted by accident. Stress and sleep-deprivation. However, I have new info if anybody would care to advise. I just opened up the drywall a bit and saw that it is foil-backed. There is a small gap between that and the brick, which is lined with tar paper. Should I tear out the old drywall? Should I leave the tar paper and/or add a new vapour barrier?

Any advice on the recommended order would be appreciated. For example, if I don't change anything, it would end up brick-tar paper-foil-backed drywall-unfaced insulation-CBU-kerdi membrane.

 

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[PorcelainVacation]

Sorry, I double posted by accident. Stress and sleep-deprivation. However, I have new info if anybody would care to advise. I just opened up the drywall a bit and saw that it is foil-backed. There is a small gap between that and the brick, which is lined with tar paper. Should I tear out the old drywall? Should I leave the tar paper and/or add a new vapour barrier?

Any advice on the recommended order would be appreciated. For example, if I don't change anything, it would end up brick-tar paper-foil-backed drywall-unfaced insulation-CBU-kerdi membrane.

 

[PorcelainVacation]

I think you should remove the drywall at the least, and I would use rockwool or closed cell foam instead of fiberglass. I think you should minimize the material that will absorb water and mold, even if you have a really good vapor barrier. Rockwool doesn't lose it's r value if it gets damp.