That PEX install looks good for the Mesh & stand offs, but looks like the PEX is too far apart for the northern climates. I'm told in Ohio you need 12" spacing, and 2 rows around perimeter 6" from outside walls. This was told to me by guy who does the installs a lot.
I got some info from a company who also has a 1/4" thick layer of foam built into the foil bubble stuff. Unfortunately that is in my email which crashed and is all gone..

thank you YAHOO.
I bought the foil bubble bubble poly for under my slab, but I'm putting it between a layer of 1" white styro and /4" blue styro sandwich. (plastic/poly vapor barrier, 1" white styro, foil side down bubble bubble poly, and then 3/4" pink/blue styro, mesh on chairs PEX-AL-PEX and then 5" concrete with fiber in 6000 mix.) this is what my floor is going to be made up of. I bought the PEX-AL-PEX and the fittings & the "Foil Bubble Bubble Poly" from Farmtek a year or two back. just prior to the prices all going up. the pricing is all back down now, reason I didn't get it in was I still had to have the outdoor pipe run prior to doing the floor. time money and loss of job kept the pour from happening for a couple years almost now... This other foil bubble foam stuff looks good I have a sample from "PRODEX"
http://www.insulation4less.com that will be going into my boots for this next winter! thanks for that IDEA!

should be just enough if I cut the stuff just right...

Mark M