How should I insulate between the house/garage?

[jeffesonm]

I am renovating a bathroom that has two outside walls, one to the actual outside and the other to the garage. It's a small room so I went with a wall hung toilet. The toilet carrier and all the shower plumbing is on the wall abutting the garage, and we get some below freezing nights here in NJ (lots below 32, coldest maybe 10?)



My plan is to basically extend the building envelope so that one bathroom wall is now inside the conditioned space by building another wall in the garage and insulating the heck out of it.

Suggestions on the best way to do this? I could frame a simple 2x6 wall and use fiberglass batts, or attach sheets of foam board and sheetrock over them, or...?

 

[begreen]

2" foam sheets will provide insulation with less buildout and no studs needed. Cover with drywall using long screws.

 

[Ashful]

Stagger and tape foam board joints, if you follow begreen's plan.


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[mass_burner]

What about the outside wall?

 

[Don2222]

I am renovating a bathroom that has two outside walls, one to the actual outside and the other to the garage. It's a small room so I went with a wall hung toilet. The toilet carrier and all the shower plumbing is on the wall abutting the garage, and we get some below freezing nights here in NJ (lots below 32, coldest maybe 10?)

View attachment 182202

My plan is to basically extend the building envelope so that one bathroom wall is now inside the conditioned space by building another wall in the garage and insulating the heck out of it.

Suggestions on the best way to do this? I could frame a simple 2x6 wall and use fiberglass batts, or attach sheets of foam board and sheetrock over them, or...?

Insulate the garage walls and get a nice r19 2 inch thick overhead garage door to make it easier to start your car and work in the garage during the winter.
I like to use R23 Roxul for 2x6 walls with R4 reflectix foil tacked over it, then sheet rock it! Also put pipe insulation around the pipes before you wall them in. I like the R4 fiberglass pipe insulation with the white backed foil tape to tape the seam but R2 foam pipe insulation is better than none! Just my 2 cents.

 

[jeffesonm]

I was thinking foam sheets would be easiest but wasn't sure if they would provide the needed R value, whatever that is.

There is someone on craigslist selling 4x8 3" R19 poly iso foam boards with 1/2" osb glued to them that could do the trick.

I was planning to leave the pipes uninsulated, with the idea they would pickup more of the heat from the house.

Insulating the garage walls is out of scope for this project.

Outside wall has some sort of foil faced fiberglass batts from 1961, whatever R value those are. They are in pretty good shape. I am actually building out another 2x4 wall on that side of the bathroom so I have room to stuff some more insulation in there... open to suggestions. I was thinking Roxul since it is water resistant. The entire room will be waterproofed with Hydroban so I don't expect any moisture back there anyhow.

 

[semipro]

I'd worry more about the outer wall than the garage wall since garage temps will be moderated by leakage from the house anyway.
Don't forget air sealing as well as thermal insulating. Doing the 2nd without the first will likely yield disappointing results.
Foam board will give you the most bang per wall thickness in general but you have to seal around it.
If you need to go batts Roxul is a great choice.
Don't waste your money on Reflectix.
The polyiso- OSB panels are great if you can incorporate them somehow. Perhaps you can build a 2x4 stud wall, fill it with batt insulation and then attach the polyiso-OSB panels to the stud faces. This will address thermal bridging through the studs and provide a useful OSB surface in the garage.