Update: added some additional details below based on comments.

I have a basement bathroom that I am currently working on. I've framed and installed rough plumbing. I have some vapor barrier problems I need to work through. I live in the Vancouver, bc area and the climate is quite mild, but we do get wet winters. I've had this house for close to 9 years and the basement has always been bone dry. We have a dimpled membrane around the foundation, which keeps the basement dry.

A note about why I'm going vapor barrier. Our local building code requires stud wall with bat (I'm installing roxul mineral wool insulation) and vapor barrier for exterior facing walls. Which is why I'm asking.

  1. The joist header is currently insulated and vapor barriered. I was planning on insulating and running the vapor barrier up and around obstacles via cutting/acoustic seal/taping. Is this correct?

  2. The furnace room, I have two choices finish or not finish.

    a. I was planning on leaving unfinished. This poses a challenge though as the vapor barrier will end and then the furnace room will be unfinished. If I was going to do this, how would I vapor barrier? If I'm leaving the furnace room unfinished, I would need to insulate and vapor behind the bathtub and up to the duct work? I was under the assumption that vapor barrier behind tile is not a great idea.

    b. The other option is to frame/insulate/vapor barrier the furnace room. How would I do this based on the supplied photos? My areas of grief are the water tank and gas pipes. A note is that we have a insulated hose that is supplying fresh air from the outside into the furnace room.

What option do you guys think is the best and which way should I go? Sorry for all the questions, I'm just trying to get as much info/questions out as possible.

See photos below:

exterior facing wall in bathroom Exterior facing wall in bathroom

bathtub Bathtub, furnace room on other side of wall.

bathtub2 Bathtub showing the ceiling

drop ceiling Drop ceiling, working around the furnace ducting

enter image description here Furnace room, How would I create a wall/insulate/vapor around this?

thanks in advance!


  • 1
    Vapor barriers aren't needed on interior walls and I don't suggest them in basements in most climates. You should try to impeded airflow from the outside by all means but don't trap water. What exactly are you worried about? Also what is your location. (From the looks of it all good so far minus insulation)
    – DMoore
    Commented Nov 18, 2015 at 23:58
  • deffinatly dont want to seal up that gas water heater room it needs air , are you putting in a barrier for a tile tub surround, if that I would put it up screw some hardy backer then tile away and seal the grout that has never leaked for me, .p.s. I did not see a fart fan or window, usually have to have one or the other in a bathroom
    – Ed Beal
    Commented Nov 19, 2015 at 0:24
  • Thanks for the comments guys. The guys at the township required that I do stud wall with insulation and vapor barrior on exterior walls, which is why I'm dealing with this. I'm located in vancouver, bc area.. climate is mild, wet winters. basement has been bone dry for 8 years.. no moisture on the test I did last year. Regarding the furnace room, there's a fresh air hose coming in from the outside, so that would't be a problem.
    – Dolph
    Commented Nov 19, 2015 at 5:44

1 Answer 1


Ideally, you would have used rigid insulation against the concrete. This would have worked as both your insulation and a vapor retarder (but not barrier). These days, vapor barriers are frowned upon in basements, as they ultimately lead to trapped moisture somewhere.

The only exception is closed-cell spray foam. That acts as a vapor barrier and insulation, but since it's applied directly against the concrete sans air gap, there is no place for water to be trapped in the first place.

Given the budget, I'd strongly recommend the spray foam solution.

Barring that, skip the vapor barrier, make sure the bath is properly vented (fan), and use a 'tile-side' waterproofer for your tub surround such as Redgard.

  • I agree with this, I was planning on going this way initially, but the city is old school (I pulled a permit) and they want stud wall, insulation, vapor.. I may look into spray foam, I'm just worried about the off gassing. Thanks for the answer!
    – Dolph
    Commented Nov 19, 2015 at 5:48

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