Houzz Logo Print

Exterior uninsulated bathroom wall and tub drain question

15 years ago

I am redoing the upstairs bathroom. It is in a brick and block house with NO insulation on the exterior wall. The exterior wall is furred with 1x5 to attach the original wire mesh and mud for tile. The wall has a 36x36 rough opening window. The tub is to be placed against the exterior wall.

I have some issues that I want to address when installing the new tub/shower:

- Because of the original tiling method that led to very thick mud and tile, I have a lot of space to make up on the ends of the tub (1.5-2 inches, walls not square)

- I want to install at least a little insulation.

My thought is to fill the gaps between the furring strips on the exterior wall with 3/4 inch thick rigid foam insulation which is essentially the thickness of the 1x5 furring strips. The rigid insulation is in several strips, none wider than 12 inches. The rigid foam covers less than 50% of the wall, and most of it is below the tub lip. The tub lip would then be butted against the foam.

Above the tub lip (not touching it) would be a sheet of exterior grade plywood run horizontally and hanging over the tub lip. Then vapor barrier, durarock (with taped seems), thinset, and tile.

The plywood would provide some limited insulation (relative to furring strips over a block wall) and provide more wood depth and screw placement options to attach the durarock.

This would be more along the lines of Mongoct posts which had the durarock fully inside the lip of the tub (my understanding of Mongoct posts).

I cannot build a 2x3 or 2x4 wall inside the exterior wall because there is insufficient space to the toilet (unless I move the toilet drain which in turn requires cutting a joist in an already small bathroom).

As an aside, based on a Fine Homebuilding article, I was also installing insulation on all of the bathroom walls to help sound proof the bathroom from the adjacent bedrooms. I placed the rigid insulation against the bedroom walls. The insulation is often in multiple pieces in order to get it behind exiting fire blocking, wiring, outlets,

So I have two questions concerning the exterior wall:

- Is there any risk that the limited rigid foam insulation may act as a second vapor barrier and cause moisture/mold issues.

- Is there any issue using full sheets of plywood as the furring.

I have a third question related to the tub train. The tub we are installing (cast iron Toto) does not have the drain on the same center line as the previous tub. Thus I need to move the galvanized piping. I plan to cut the piping a few feet from the tub and replace with schedule 40 PVC. To join the PVC to galvanized pipe I was going to use a rubber boot with hose clamps (1.5 to 1.5 inch). (I really donÂt want to try to get galvanized pipe to line with the tub drain.) Is there an issue with this method to join the pipes? Is there a better method?

Thanks for any help.

Finally, I have read many of the very informative and helpful posts and appreciate the time, exceptional expertise, detailed/informative answers, and etiquette that has been displayed in this forum. Particularly note to Mongoct and Bill.