Sauna moisture control

Q: How should I protect my house from the moisture given off by the sauna I’m building? Do I need an exterior vent of some kind?

A: Your concern about moisture affecting the rest of the house is valid. You don't want to boost overall humidity so much that it harms the rest of your building. That’s a very real danger, especially in cold winter weather. I'd suggest you build the sauna framework, seal its walls with a vapour barrier, moisture-resistant drywall (taped and painted with vapour barrier paint), then apply tongue and groove cedar to the inside. To prevent moisture from escaping to the rest of the house through the doorway, create a transition zone outside the sauna, using another wall and door. This area should be vented to the outside with an exhaust fan. You can’t vent the sauna directly because that’ll defeat the sauna’s purpose by drawing all the super-heated air outdoors.