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Garage Vapor Barrier

SeanRyan | Posted in General Questions on

Hey All — I’ve found similar questions but can’t seem to locate one that hits exactly this.

Foundation is a basement — half is a drive under garage and the other half is a finished basement space. Living area above both. Shearwall diving the two sections.

The finished basement will have subslab foam insulation and Stego wrap and will be tightly air sealed from the garage portion. There will also be a passive radon system on this side only. 

The garage side will have no subslab insulation. However, I’m curious if it needs any vapor barrier? There seems to be some confusion online on this topic. 

Would you add a vapor barrier below the garage slab?

Also, since the garage will be completely air sealed where it connects to the house, would you worry about adding any radon mitigation to the garage side of the slab? 

Thanks,

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Replies

  1. matthew25 | | #1

    Yes, your garage slab should have a vapor barrier. Especially so far below grade, you will have big moisture intrusion and humidity issues all the time without one. Would you ever want to apply an epoxy coating on that slab? Try doing that when you have moisture intrusion, it will ruin the finish of the epoxy and look horrible.

  2. Expert Member
    Michael Maines | | #2

    I would include a vapor retarding membrane. I would also include some insulation, as there is a good chance you'll eventually want to heat it in cold weather and in warm weather an uninsulated slab will absorb condensation if it's much cooler than the air.

    Is there any kind of break in the slab between the garage and the lower level living space? If not, I would want to capture radon from the entire building perimeter, since below the slab the radon won't know where there is garage and where there is living space.

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