I shall be extending my house in the new year so I'll probably have a ton of questions here and here's the first! If I remember rightly, some 15% of heat is lost through the floor, so is there some form insulation I can install into the new floor (which will be concrete/screed) and whereabouts does it go? Between the concrete and the screed?
Have a look on the springvale and crown websites. Most are laid under the concrete slab and are really little more than polystyrene slabs that interlock.