ᐅ Which vapor retarder or vapor barrier should be installed in the bathroom?

Hello,

I want to completely renovate my guest bathroom and would like to know which vapor retarder or vapor barrier is best to use for moisture control. Since I will be opening up everything and moisture regulations for wet rooms differ from those in living rooms regarding construction, I don’t want to use the cheapest materials but rather good, durable products.

Unfortunately, I am quite overwhelmed because there are so many specifications when choosing materials (sd-value, variable vapor permeability, diffusion resistance, etc.), so I am now seeking help.

An additional question is whether I can also use this membrane for the wall construction since the guest bathroom wall faces the exterior and is poorly insulated (thermal bridge).

Canadian wood-frame prefabricated house, built in 1977
No roof insulation/attic insulation (guest bathroom is directly under the attic)
Bathroom window for quick ventilation is present
Standard heating system will be removed – underfloor heating will be installed
Planned installation: battens/membrane/counter-battens/moisture-resistant drywall panels

Thank you and best regards

Hello,
using a vapor retarder with an sd-value of 2.0 is the right choice (Würth, Isover, Ampack, etc.). Question: why don’t you want to install insulation if you are tearing everything out anyway? If there is no insulation present, you usually don’t even need a vapor retarder...