Glossary
Design of a certified Passivhaus building

U-Value

This is the thermal transmittance coefficient (also known as the thermal insulation coefficient). It is expressed in W/(m²K) and determines the heat loss (expressed in watts) through a surface (expressed in square meters) based on the temperature difference (expressed in Kelvin) on either side of it.

Thermal Phase Shift

This is the phenomenon that occurs in the summer, when a building accumulates heat and then releases it gradually throughout the interior, with a time lag that varies depending on the building’s thermal inertia. The phase shift represents the time lag between the peak outdoor temperature and the peak temperature inside the building. It is therefore considered an asset for summer comfort because it delays heat transfer through the building’s walls during the day.

Grey energy

Grey energy is the amount of energy consumed during the...