Direct to stud surround and tub install

[Faderus]

Hi, I am installing a Sterling Ensemble tub and surround into a 1960 construction raised ranch with the long side of the tub on an exterior wall (in upstate NY) . I have 2 questions...

The existing rough in is pretty big. Would it be improper to sheathe the studs with a water resistant ply to make up the space?

Would it be detrimental or beneficial in any way to use spray foam on the back of the surround and tub to limit water heat loss (current install has a cast iron tub and probably no functional insulation to the exterior wall so is a giant heat sink.)

I was planning on installing rock wool insulation, any issues? I am a fan of spray foam but since this is such a small area, it is probably not cost effective to use here, unless I'm missing something.

 

[Jadnashua]

I would just shim the walls so the fit is acceptable. That would also help you to potentially fix any stud that is not in plane with the others.

Adding insulation in the walls doesn't hurt.

The surround itself should be totally waterproof, so the expense and hassle of moisture resistant ply or even studs behind the surround is a waste of money and, they tend to warp as the dry out, which could cause issues later. If you insist, look for KDAT (kiln dried after treatment), at least those should be stable.

Many of those type of tubs work better longer if you bed them in some mortar so that the thing is both level and the bottom is solid. Flex is annoying, and can lead to crazing and eventual failure, so stopping potential movement is important.

If you're shimming things, take the time to help ensure that your corners are both plumb and square...the thing will fit in there (well, it should!) much better, and make it easier to keep all of the seams intact and watertight.

 

[Sponsor]

 

[Faderus]

Thanks. I was thinking the ply would create something of an enhanced vapor barrier acting to keep any steam from condensing in the wall. As I type it though, the hot side would be inside the shower not the wall. Basically cheap insurance, but I hadn't thought of the drying out warpage. I plan to bed it.

Any thoughts on adding spray foam to the tub/wall bodies?

 

[Jadnashua]

Adding some spray foam shouldn't hurt as long as you don't overdo it and then require the thing to warp when trying to get it in position to the studs. Not a great idea on the bottom. There are structural foams, but not in a spray.

You should not get any moisture behind the walls of an engineered tub surround - they're waterproof as is if your seams are proper. Now, if you were tiling the thing, neither tile nor grout are waterproof, and a moisture barrier is required.