Certified Passive Houses require slab edge insulation: a 100 mm concrete slab sits on 100 mm of rigid foam, fully isolating it from the ground. This stops thermal bridging where walls and windows meet the slab, keeping cold from penetrating the concrete.
One of the key things with certified Passive Houses is that behind the slab edge insulation, you've got the concrete slab, which is 100mm thick, and then underneath the concrete slab before the footings, you have another 100mm of foam. So the actual slab for the house is completely isolated from the ground and insulated, and this slab edge insulation makes a huge difference to making sure that the junction between the wall of the house or a window and the slab is, is protected from cold kind of getting in and running into the concrete. That's one of the, one of the key features that you see on all certified passive houses.
