A few months ago I posted a message about applying radiant heat over an uninsulated slab. I got a couple replies (thanks, wetheadwarrior and brooklyn), but I cannot find my original post, nor recreate the thread. So I’ll try again:

I’m converting a 24×20 carport into living space. I want to use electric radiant heat in the thinset beneath the tile finish floor. How well will this work without any insulation under the slab? The slab is dry, as it is poured over 3′ (that’s right, 3 feet) of rock that I used to fill a previous owner’s attempt to create a sunken living room. Since I don’t want a step up into the room, I prefer to avoid the usual barrier/foam/sleepers/subfloor approach to the problem.

I live in the Pacific Northwest; winter temperatures rarely get below freezing. The walls are framed with 2x6s, so I can apply plenty of insulation. The roof rafters (also 2x6s) will form the vaulted ceiling.

Will a radiant barrier suffice? How about that bubble-wrap-sandwiched-between-foil sheets stuff?

My inquiries to the manufacturers of the radiant heating products yield only their stock application specs.