Moisture barrier versus air barrier underneath slab
Myrtleboone
| Posted in GBA Pro Help on
I plan on building a house on a slab later this summer (northern Maine). I have been planning on installing a 6 or 10 mil poly air barrier underneath my slab (and above my rigid foam) which would extend upwards from the edges of the slab and seal to my polyethylene air barrier located at the inner wall of my double wall assembly. Does the poly under the slab effectively block moisture or am I better off installing a vapor/moisture barrier to avoid moisture transfer into the slab, but at the same time continuing my air barrier under the slab? Thanks.
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Replies
Matthew,
Polyethylene is a vapor barrier. It's a good idea to have a vapor barrier under your slab.
You don't need an air barrier under your slab. Concrete is an excellent air barrier. As with any air barrier, don't forget to seal air leaks at the perimeter and penetrations with a high-quality caulk.
Thanks Martin. So I could install poly for the slab vapor barrier (which would address the potential air leaks at the slab edges-as I will extend it upward from the slab edges) , or would I be better off using a dedicated vapor barrier?
Matthew,
Polyethylene IS your dedicated vapor barrier.