Insulation, Radiant and Vapor Barriers - Vapor Barrier for insulated built-up floor on slab

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jwm2
10-01-05, 10:03 AM
I am building up an existing slab floor to match the rest of floor in the house. I will be installing 2x6's over the slab and then the subfloor. I am going to use R-19 in the floor with paper barrier towards indoors. Should I put a vapor barrier on the slab first? If I do, then I will effectively have a vapor barrier on both sides of insulation (moisture problems?).

Existing slab has old vinyl floor. Will that suffice for a vapor barrier.

Thanks

twelvepole
10-02-05, 07:34 PM
You are on the right track. Vinyl will act as vapor retarder. And you will need the additional vapor retarder to prevent warm, humid air from condenses in the floor cavity.