This International Standard specifies a method and provides conventions for the calculation of the steady-state transmission and ventilation heat transfer coefficients of whole buildings and parts of buildings. It is applicable both to heat loss (internal temperature higher than external temperature) and to heat gain (internal temperature lower than external temperature). For the purpose of this International Standard, the heated or cooled space is assumed to be at uniform temperature.

Annex A provides a steady-state method to calculate the temperature in unconditioned spaces adjacent to conditioned spaces.