Just thought I'd better check before I hit secondsandco. The kingspan/celotex foam board to be used under the floor slab, as my solid floor is spec'd, so bearing the weight of 6" of concrete. Can the standard board be used for this - i.e. yellow fibrous, foil on both sides ? Or do you need a special stronger board for use under the slab ? (i.e. kingspan make some kind of "kooltherm K3 floorboard")
Thanks, Simon.