Opinions on installing radiant in basement

[mikek]

I'm in the process of finishing half of the basement in my house (~400sq ft) and would very much like to install radiant floor heating as I've never found basements that are heated with forced air to be very comfortable. Ideally, the heat would come from solar water panels, but that's a future project....likely another post as well

Anyway, the basement is currently got an uninsulated concrete slab and is constructed out of wood (2x6 on 12" centers). I plan to insulate the walls (trying to decide if I should have it done with spray foam or use fiberglass, again another post!)

I'm guessing that any attempt to put a radiant floor down without insulation over the floor will only result in the worms in the ground being a little warmer and my basement not getting much of the heat.

My questions would be, how much insulation do I need to make a difference? I've got a height constraint as the floor to ceiling distance is already a tight, so I can't add 2" of insulation + a subfloor and finished floor. I'm thinking of 1/2" insulation, 3/4" subfloor with PEX embedded and a 1/4" finished floor (likely an engineered floor, cork maybe?).

If this much insulation can make a difference, what kind of products are out there to facilitate an installation like this? While looking for answers in this forum, I ran across Olaf Piesche's blog and am very intrigied by his DIY installation method. Would something like that be suitable for my basement? I should note that there's never been a moisture issue. While I was moving my shower drain, I found that there is a vapor barrier under the slab, along with at least 6" of pea gravel (though that may only be around where there is plumbing?).

Thanks in advance for any information!
mike