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bsande2 01-22-2012 04:43 PM

Condensation on concrete floor under basement fiberglass shower/tub insert
I have a finished basement with a concrete floor. In the basement bathroom, I have a one-piece fiberglass shower/tub that rests on the concrete floor (blocked up on the 4 corners about 1 and 1/2"). The concrete floor is cut out about 6" x 12" to accomodate the plumbing on the drain end of the unit. The bathroom is not on an outside wall but, it is only approximately 3 feet from an outside wall. There is a small closet between the bathroom and the outside wall. The long dimension of the tub runs parallel with the outside wall. The bathroom dimensions are 8' 3 " x 5' 0" x 7' 9" high ceiling. I have an exhaust fan that is rated at 50 CFM. It is switched independently from the light so, may not be turned on with every shower.
The problem I am having is there is water condensation forming on the concrete floor beneath the shower/tub. It has been bad enough that there is absorption into the sheetrock on the wall of the adjacent closet and there has been some signs of mold at the top of the baseboard.
My question is can I put some kind of insulation between the shower/tub and the concrete floor to eliminate the condensation of the cooler concrete floor? Is the exhaust fan size sufficient to exhaust the excess moisture from the bathroom? How much gap do I need under the bathroom door to allow full air flow out of the exhaust fan? This area is sealed up by sheetrock and I can't monitor it so I need to be sure I have alleviated the problem before I seal it back up. Would it be to my advantage to have a ventillation grille cut into the wall to allow more air to flow into that area under the shower/tub?

Thanks for any assistance you can offer,

joecaption 01-22-2012 04:57 PM

Does the fan run to the outside of the house?
Was there any vaper barrier and foam board added under the slab before the pore?
The fan has to be run everytime that shower is used and allowed to run for at least 10 min. after every use. They make fans with a humidistate that come on automaticly when it's damp in there. Panisonic makes one.
I would also run a dehumidifyer in that basement. It's going to start causing problums in other areas down there.

bsande2 01-22-2012 07:02 PM

The exhaust fan does exit to the outdoors. I can feel the air flow outside at the vent exit. As far as the concrete, I don't know if there was any barrier or foam put down underneath. It was done by a fairly reputable local contractor so, I can only assume that it was done correctly. I do know there was some drainage pipes installed under the basement flooring to help with drainage. Is there anything I can do as far as insulation under the shower/tub? That could be in addition to running the fan longer an running a de-humidifier.

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