Radiant heat install

[JECulver]

I am starting my radiant heat install in a Barndominium. I'm in central Montana and my first question is about vapor barrier under the insulation board under the concrete. Is it necessary? We live in a very dry climate so I'm thinking it will not be needed. What are your thoughts.
Thanks John

 

[jack stand]

If you're slab is truly high and dry my understanding is that no it's not necessary. You're still insulating right?
I'd be tempted to spend the $150 for the poly and just do it.
https://www.greenbuildingtalk.com/Forums.aspx this is a good site to ask a question for a lot of building questions about radiant and insulating techniques and materials.

 

[road_king]

We put a vapor barrier down under the 2"foam. Some say put it on top of the foam. Either way, best to use a vapor barrier.

 

[purediesel]

What's a few hundred dollars for the piece of mind that there is no chance to get moisture into your slab and into your house?? I would be using a Class A vapor barrier if it was my house and not some cheap poly. My 50x80 was around $6-700 with the proper vapor tape.

 

[Firebrick43]

Put it down, it might help keep issues from happening in a wet year and it helps keep the concrete moist so the ground doesn't **** the moisture out and stop the curing chemical reaction which will result in lower strength of the concrete.

I suggest stegowrap. It goes on top of the foam.