[Greenbuilding] Hydronic Radiant Underfloor Heating

[Bruce Donelson]

Most concrete contractors put a couple of inches of sand over the foa (and
under it) to absorb the bleed water while the concrete sets. Sand also
compacts quite well when dampened, and levels easily to support the foam
without voids which could promote cracking later.

So my jobs layer out more like:
1. Dirt and crud
2. Gravel fill if required.
3. Sand (or decomposed granite, which is locally available and more
angularly granular.)
4. Foam. (Pinkboard. Rated for compression strength. 3" ) (Lower compression
foam can be used down the sides of the building to minimize heat loss at the
perimeter, where the building is coldest.)
5. Black poly.
6. Rebar grid set up on Dobes (little concrete blocks with tie wire
embedded.)
7. Pex-Al-Pex. Intalled in a pattern that does not take it under walls.
Enters and leaves rooms by the doors. Spacing and length of run determined
by my heating sub. Pex is tied to rebar grid and pressurized. That way you
can tell if it gets hurt, and when.
8. Concrete. Scored about 1/2"

On my last job, the concrete was ground down with diamond pollishing tools
to an 800 grit, dyed, hardened with Silicate formulation called RetroPlate
(good article on concrete polishing in Environmental Building News about a
yar ago,) then touched with a stain repellant. Quite attractive. Very Green.
No waxes, strippers, vinyl, carpet. Maybe a gallon or so of acetone was used
with the dye to dye about 3000 square feet of building. Wears for many years
before a quick rebuff if kept reasonably clean. And the building has a
stunning appearance overall.

Bruce Donelson
A Better Builder