U-Value

Thermal transmittance coefficient of a building component in W/(m²·K) — key performance indicator for energy efficiency according to GEG.

The U-value measures heat transmission through a building component in W/(m²·K). It comprises lambda-value × layer thickness plus surface resistances.

Reference values: uninsulated existing building ~1.5, new construction today ~0.2, passive house ≤0.15, triple-glazed insulating glass ~0.5. The GEG sets maximum values per building component.