This article assumes you've removed any drywall and are now down to bare studs in the room, and bare joists on the ceiling, and a non-permeable floor. Tile, cement, vinyl are suitable non-permeable floors. It's good to at least put some tile under your sauna heater, although plywood will work. Or anywhere water may accumulate. If you must go with plywood, definitely overlay with duckboard flooring. How to Build a Sauna: Wiring for Light Wire your room for a light, light switch, sauna heater wire conduit, and perhaps controls outside the room. If preparing for a gas sauna heater, then you're using gas pipe and you'll have to consider the thickness of the pipe and how many other appliances share the gas line. Consult your gas professional. How to Build a Sauna: Insulation to Lower Operating Costs Insulate your walls with R-11 insulation for interior walls, and R-19 for exterior walls. Fiberglass insulation is available in either 16 inch or 24 inch wide rolls. Insulation lowers your operating costs by keeping your sauna heat in the sauna, so don't skip this step. And sauna insulation will also provide a sound barrier, so you relax more deeply which is what it is all about, as well as a good healthy sweat. How to Build a Sauna: Foil to Reflect the Heat We attach the sauna foil to improve insulation and as a vapor barrier The sauna foil vapor barrier adds a R-1 value to your insulation factor, and acts as a vapor barrier. Staple the foil vapor barrier to all interior surfaces, ie the wall and ceiling. Generally, we overlap the foil by 3 inches eliminating the need for the foil tape. Also don't substitute another product for the foil. The foil will never melt and is odorless. propane sauna heater protects your walls from absorbing vapor. Some steam in a sauna room is great to help bring on a sweat, but it creates humidity that should be isolated from the rest of your house (or spa). My website: http://www.saunaguides.com