A U value of 0.15 W/m²K should not be exceeded, because good thermal insulation is an essential prerequisite for cost-effective, energy-efficient buildings. Good thermal insulation is also a prerequisite for real comfort indoors.

In the case of timber structures, the rafters or beams should be slim and tall, so that the insulation can be 30 to 40 cm thick or more. Mutatis mutandis this applies to flat roofs, too.

The base of a passive house should not exceed a U value of 0.15 W/m²K, either. The easiest arrangement to implement is a thermally really well-insulated floor slab. 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.

Among others, the following aspects must be taken into account for passive-house windows:

• Glazing with U_g of at most 0.7 W/m²K
• Thermal-bridge-minimized edge seal on glazing, with a thermally optimized spacer made of plastic or stainless steel (with minimal wall thickness, less than 0.2 mm) and a resulting loss coefficient Ψ_g of at most 0.035 W/mK
• Deep edge-seal overlap within frame