Interesting post dub_nerd
Basically top spec insulation means that air temperature might not drop much overnight, but without any top-up from the heating system, the underfloor could potentially drop 1 degree per hour. If the stats arent calling for heat due to the room temperature maintaining its level, yet the slab is down in temperature, how does one ensure that the slab doesnt drop too much so that it needs to make up a significant shortfall in the morning. Assuming the slab is set in a tray of insulation with insulation underneath and the sides turning up to ensure the underfloor slab makes no direct contact with the wall, could the slab retain its temperature for a greater amount of time?