The second pour encases the ductwork within a thermal mass of concrete. Warm water and an accelerant was used in the concrete mix due to winter temperatures.
The homes forced air system will pass a series of ductwork through the slab creating a "heat energy battery". In this image 8" round ductwork is being tied into the central trunk line.
A high compressive strength foam board was at point loads and bearing wall locations. The foil faced insulation board, which has a greater R-value was used everywhere else.
Electrical conduits were run to the home's load center. The conduits will be allow future access to the panel without disturbing the thermal envelope.
Here the forms are up, the vapor barrier has been placed, and two layer of rigid foam are being installed prior to the first concrete pour. The foam is fit tightly with staggered joints and taped seams.