[Greenbuilding] Insulating a slab

[Lynelle Hamilton]

   I'm certain this has been covered before, but I am looking for the "best"
   way to insulate a concrete slab for a slab on grade home.  I have some
   questions:
   I'm considering building a passive solar home with an insulated slab on
   grade (no crawl space).  The home would have a partial upper floor for two
   bedrooms and a bath, but all main living areas would be on the lower level.
   The north side of the home would be placed into a hill that gradually rises
   to the upper level, so that I have on grade access to the upper level from
   the north and on grade access to the south/east/west for the lower level.
   The lot is sand/sandy loam and slopes to the south.
   I have a home with concrete floors now, so am somewhat used to not being
   able to move things around easily when they are embedded in concrete.  I do
   want a warm environment and don't want to be heating the ground below the
   slab to the extent that I can avoid it.
   Does anyone have any suggestions as to how best to do this?
   Thanks for any ideas!
   Lynelle Hamilton