If you have enough ventilation than you should be fine. I put my new bathroom fans on timers. They run for an hour after I leave the bathroom (10, 20, 30 and 60 minute increments). If that were my bathroom, I'd want a vapor barrier to prevent the moisture from getting into the walls. I live in Alaska, so the concerns are the same here. My vote is for a vapor barrier and plenty of controlled ventilation. Be sure to not only use a timer on the fan (Panasonic Whisper fans are good) but also be sure that the exhaust line is insulated.

Hi illinigirl, The standard insulation used under basement floors is rigid insulation (XPS -- extruded polystrene). It comes in 2 inch thick often blue pieces of styrofoam. Dow manufacturers it among others. It is not spray foam. We used it in our build -- we are in southern Canada. The labour to lay the rigid insulation sheets was not high. The guys had to dig away a bit more gravel so the basement ceiling level was not compromised. They used the red tuck tape to attach the sheets to each other. This allowed the concrete flat workers to pour the floor with wheel barrow loads. I am not sure yet what a difference it will make as we are partway through our build. We have hydronic in-floor heat that was just turned on for the basement level. The floor is wonderfully warm (mostly due to the in-floor coils). We were required by code to place the rigid insulation because of our planned in-floor heat. Otherwise, I understand, the heat from the coils would not just heat upwards and instead would have been wasted heating underground? We did place the rigid insulation around the perimeter of our our unheated garage. I will go and step on the parts of the garage floor that have the insulation vs the parts that don't to see if I can detect a big difference and report back. Our architect spec'd for this rigid insulation under the basement slab. At the time, we had not planned for the in-floor heat. In other words, he felt it was a good practice even without in floor. The rigid insulation sheets are not cheap. We paid $25.00 a sheet (each one is 2 feet by 8 feet). We are in Canada where everything seems pricier. You can calculate the area needing coverage and see how much your builder is charging for labour vs material to help you decide if the price is reasonable. Don't forget the tack tape is also not cheap. Best of luck. Carol

"Blueboard" is very thin veneer plaster on gypsum wallboard that has an absorbent facing but no treatment for moisture resistance other than a harder more durable finish over the entire wall. Blueboard is not available in many areas of the US but where it is available it should be the standard choice in all rooms of the house. The concept of a house needing to "breathe" is often misinterpreted. It means a that any moisture in an exterior wall should be able to move to the dryer outside air in a cold climate and to the dryer inside air in a hot climate. The air quality of the interior spaces should be addressed with exhaust fans and heat recovery air exchangers and/or by opening a window not by moisture or air moving through the exterior wall. In a cold climate, moisture inside the house needs to be prevented from passing into a conventionally insulated exterior wall by a vapor barrier in order to prevent it from condensing and freezing on the inside face of the cold exterior sheathing. I can't imagine why two layers of drywall would be recommended unless it was to reduce the penetration of noise from outside through an exterior wall that contained no windows.

thanks, i finally found one youtube from "this old house" that showed i can put fiberglass right on top of it. But thanks for your time, always appreciated.