Day 11...

Since Debs' post this morning, by the time the crew left at the end of the working day the hardcore and type 1 material was in with sand blinding on top ready for the insulation to be installed. This point marks the first departure from conventionality, as the next stage is to install 200mm of polystyrene insulation ready for the 20 tonnes of concrete slab to be poured on top of it.
Usual practice is to pour the slab at this stage, then insulate it and pour 50-70mm of screed on top within which the underfloor heating pipes are installed. We're cutting out the screed and going for a single pour of 150mm, which will will also contain the underfloor heating pipes within this massive slab.

The theory behind this is that we will be using a lightweight (timber frame) structure to build the house, this being common practice in Scotland and fairly standard in Scandinavian countries and North America. Whilst there are many advantages of timber frame construction over heavyweight masonry, well insulated timber buildings can be liable to overheating in summer and internal temperature/comfort levels can be difficult to stabilise. Introducing 'thermal mass' elements into the structure compensate for this...which is where the heavyweight floor slab comes in. In addition we have specified high density wood fibre and mineral wool insulation for the walls and roof which will also add to the thermal mass of the building as a whole.