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joegambler 09-18-2009 11:17 AM

To Vapor Barrier Or Not to Vapor Barrier, That Is The Question.
I'm redoing a shower. I'm using 3/4" moisture resistant foam sheet insulation on the exterior block walls and furring strips over that (same way it was). Then cement board and a waterproof membrane. The problem I'm having is the foam that I took off had foil on both sides. I'm assuming that is a vapor barrier. I haven't seen any foam insulation that has foil. And the insulation companies have been useless in telling me if I need a vapor barrier or not. I'm not worrried about codes, just doing it correct. Do I need a vapot barrier? By the way the house is in central Florida. Thanks.

Mop in Hand 09-18-2009 11:47 AM

Adding a vapor barrier on both sides of the cbu will create a moisture sandwich. install one or the other but not both. I am assuming this is an exterior wall.

concretemasonry 09-18-2009 12:54 PM

some types of foam bords need a foil barrier to eliminate off-gassing that will reduce the insulation value in the end.


joegambler 09-18-2009 01:25 PM

Mop in Hand
I don't understand your reply. The foam I took out with foil on both sides was there originally from the builder. I'm not adding a vapor barrier to both sides of the cement board. The waterproofing membrane I'm using on top of the cbu is to waterproof the shower under the tiles. I just need to know if regular 3/4" foam board with no vapor barrier on the exterior wall is correct. Thanks.

joegambler 09-18-2009 01:28 PM

From what I understand from your reply is that the foil doesn't necessarily make it a vapor barrier. O.K., I still need to know if no vapor barrier or yes. Thanks.

Mop in Hand 09-18-2009 09:40 PM

No foil is needed. You do not want a foil/moisture barrier if you are using Redgard or the like on top of your cbu.

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