Floor slab and basement ceiling

The base of a passive house should not exceed a U value of 0.15 W/m²K, either. In general the downward heat loss coefficient is of the order of 0.6 down to around 0.2 for very extensive buildings; the thermal insulation should be planned accordingly.

The easiest arrangement to implement is a thermally really well-insulated floor slab.

Floor slab with insulation layer (source: Arch Wimmer – schulze darup & partner)

Ideally we have a load-bearing floor slab in contact with the entire insulation layer, which then merges into the wall insulation over its full thickness.