Best Adhesive for Underfloor Heating?

[epurdy]

thanks for the advice. decided we've got too much bounce and we're going to pull up the chipboard and the kingspan and lay down a base of joists. don't think we'll be able to attach it the brick/earth floor but hopefully should give us a stable base.
will stick the kingspan in the middle of this and then top with chipboard or plyboard? any advice? preferences on type and thicknesses?? neither will be the surface to take the tile as will add on insulation for the UFH where required and plyboard for under the cabinets.