Energy Star Home Retrofit: class II vapor retarder required over existing slab
NateFournier
| Posted in Green Building Techniques on
This house has a fieldstone foundation in Worcester, MA. Part of the Energy Star certification requires the basement slab to have a class 2 vapor barrier over it. Ideally, I would like to use a liquid-applied solution, but a self-adhering sheet product would work as well. I cannot, for the life of me, find anything that seems to work…
Any suggestions?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Hi Nathan.
Just to be clear, it has to be class II (can't be class I)?
Could you use rigid foam insulation that qualifies as a class II vapor retarder and get the thermal benefit as well?
I believe some of the epoxy basement finish coatings (or radon sealers) would hit the right range.
I'm pretty sure Class-I vapor retarders would also qualify. Can you point to an online version of the Energy Star requirements where that's specified?
https://hp.seal-krete.com/products/vapor-shell/
https://ghostshield.com/product/vapor-tek-440
Are you going to be finishing the basement into living space? If yes, a 5/8" plywood subfloor on top of an inch or two of Type-II or Type-VIII EPS (pretty cheap at your local Green Insulation Group's reclaimed or factory seconds pricing) would be in the Class-II range. But in that case I'd personally still prefer a <0.1 perm Class-I sealer (or 6-10 mil polyethylene) on the slab itself.
In Wormtown uninsulated basement slabs can be on the cool side for bare feet, but usually not downright frigid. The cooler spots in my (ZIP 01609) uninsulated rat-slab basement with reasonable wall insulation but no active heating still run in the low to mid 50s F sometimes.
It can be Class 1. I considered foam, however, this is a flip and I didn't budget to finish the basement so I would like the vapor barrier to be a clean and durable finish.
These epoxy products look like exactly what I'm looking for. I talked to my paint supplier and he HIGHLY discouraged using epoxy on an older slab (1943) but I don't know what his opinion was based on.
Hi Nathan.
Since class I is acceptable, here's another product to consider: https://prosoco.com/product/vb-vapor-barrier/