Under slab vapor barrier

[slowTA]

I'm getting ready to do my foam insulation for radiant heat and the question came up of where to put the vapor barrier. I understand that the foam insulation can be taped together as a vapor barrier, but that may not be the preferred method.

Typically the vapor barrier goes between the stone and concrete. But when you add 2" of foam insulation should the vapor barrier stay against the concrete or the stone?

In my other thread the argument for on top of the insulation and PEX means any dirt won't float up to the top of the concrete. This would also be easier on me since I won't have to worry about huge sheets of plastic to keep the foam from sticking to the skirt board. I was going to use construction adhesive instead of screws/nails to keep from penetrating the moisture barrier.

What say you?

 

[kj_mustang]

Over the stone, keeps moisture away from the foam too. Wrap the plastic up just enough to staple to the lower part of the skirt board. You can still glue the foam used to insulate the sides of the slab to the skirt board.

 

[slowTA]

Got it, so you don't need to pull the plastic up a foot or so beyond the top of the skirt board.

Another option I came up with was to attach the foam to the skirt board then put down the vapor barrier... but that seems like an idea from someone who can't make up their mind!

 

[Chris705]

My thought on my build was VB under insulation board....the insulation will then protect the VB from damage during conc. placement....and I used the WWM at the bottom of my pour to anchor the pex to with zip ties so the insul further protected the VB during this work also.
I am not sure what the concern for dirt floating up really means....AND not sure if you really intended to say VB on top of the pex? Cause I am pretty sure that isn't a good idea, I think as much encapsulation of the pex with concrete is preferred. I counted on the concrete cement paste working its way down and almost all the way around the pex when installed directly on top of the WWM, which was on top of the insul. board.

 

[yeldogt]

You will get different answers -- I always use a heavy VB on top of the stones. Foam on top of the VB.

I typically tape the seams -- mesh to hold the PEX w/ zip ties.

The tape will hold for a reasonable time and keeps everything nice and together for the pour.

 

[tricountytrail]

The shavings and little pieces of foam will get all over top of board. I will blow mine out and use Vapor Barrier mesh then pex. Insulation was easy to install.
I screwed perimeter board with cap washers and 2 1/2 inch screws.


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