I'm using kerdi membrane for my shower area with cement backerboard. Should I still add a layer of plastic vapor barrier behind the backerboard. Normally that's required to prevent the studs and insulations from wicking up water from the cement board, but I've seen discussion about water being trapped in the backerboard if the board is lined with Kerdi on one side and water vapor barrier on the other side. What about the rest of the bathroom, vapor barrier behind greenboards? Any definitive answers?
Vaper barrier for kerdi lined shower walls
bathroomcement-boardvapor-barrier
Related Solutions
No, there's no need to install a vapor barrier between two conditioned spaces. The purpose of a vapor barrier is to prevent warm moist air from traveling through the insulation and condensing on the cooler side, which can easily happen in cold climates. With a conditioned space on both sides, you can allow any moisture in the air to pass through.
There's also no need for insulation except for sound proofing (fires can pass through doors, as can any heat). For sound, make sure your insulation is designed for that, and also consider a resilient channel or similar product that will keep the drywall physically separate from the studs, which is how many sounds travel through walls.
You should NOT place a vapor barrier BEHIND the backer board.
Where, pray tell, would any such collected vapor/water go?
Answer:There's nowhere proper for such moisture to egress.
The current best practice is to place waterproofing OVER the backetboard and just UNDER the tile. Thin sheet membranes like Kerdi or NobleFlex are examples . Paint on membranes can also be used, such as RedGuard or AquaDefense.
This a is a recent job I completed illustrating Kerdi over Hardibacker.
Related Topic
- Shower – What are the insulation options around a shower
- Water – Vapor and moisture barrier for “above ground” basement
- Shower – Properly waterproofing a shower area sharing a living room wall
- Water – double vapor barrier
- Drywall – tearing out tub/shower surround
- Vapor barrier on Bathroom tub exterior wall(s)
Best Answer
Kerdi is your barrier if properly installed it will stop water from migrating. I don’t recommend a barrier behind green board it is better than standard sheetrock for moisture but sealing it may cause more problems than can be gained. A good quality exhaust fan with the lowest noise or Sones will do be the best way to go.