I'm about to start a diy radiant job that consists of ceiling radiant heat and possibily part of that system being radiant wall heating, in the northeast a typical insilation job consists of using unfaced fiberglass batts and installing a separate 6mil plastic vapor barrier over it and then your sheetrock (wall installation) for the ceiling I plan on covering the trusses with 6mil plastic then sheetrock and then blowing loose cellulose in the attic. Now my question,.should I install the PEX tubing under or on top of the 6mil vapor barrier ???? I guess I should add that the way the pex and the transfer plates will be attached to the the studs/trusses will be first 3/4"x3" pine furring strips will be installed with the pex/transfer plates "recessed" into the gap between the furring strips.

Hi Joey,

The vapor barrier, as always, goes on the warm side of the insulation. The purpose is to arrest the water vapor that exists within the warm space. It's like being in your pickup truck (you know, the one that froze last week). Water vapor from breathing condenses on the windows. The same is true within a house. You want the insulation between the water vapor and the cold so that it won't condense in the insulation and destroy the insulating value.

Trust me.

tom

without a doubt understand where the vapor barrier goes and why, wondering if I should install the radiant wall/ceiling system on top or under the vapor barrier. I'm guessing on top of the barrier because the 6mil plastic may "hold" back the radient heat and possibbly warm the fiberglass leading to condensation.....thoughts ?

yes, warm side of the insulation, which is behind the radiant panel. simply from an installation standpoint you probably don't want to obscure where the tubing is when you are screwing up your sheetrock as well.

(edit: removed old contact info).

[This message has been edited by NRT.Rob (edited 01-22-2005).]

thanks Tom and Rob.

what's the rule of thumb for a basement staple-up ? Should the kraft paper be facing the basement or the floor above? Does it matter if the basement is finished?