In Tucson, houses are built on sand. The house is not thermally insulated from the ground, thus, the thermal building model ought to take into account the exchange of heat between the house and the slab underneath it.
The slab is modeled with a single conduction layer connecting the temperature of the slab to the temperature of the floor. Above the floor, there is a boundary convection layer.
.BondLib.Examples.SolarHouse.Slab