More insulation for the floor slab

I've attached 70mm polystyrene to the outside edge of the floor slab using polystyrene left over from the build.
The majority of heat loss from the floor slab will be through the outside edges, 70mm of poly should reduce this considerably. The poly will be in contact with the ground so won't last indefinately but a couple of coats of sealer (more left overs) should extend its life greatly.