This standard specifies the equations to be used in a simulation method for calculating the non steady transfer of heat and moisture through building structures. It also provides a benchmark example intended to be used for validating a simulation method claiming conformity with this standard, together with the allowed tolerances. The equations in this standard take account of the following storage and one-dimensional transport phenomena: • heat storage in dry building materials and absorbed water; • heat transport by moisture-dependent thermal conduction; • latent heat transfer by vapour diffusion; • moisture storage by vapour sorption and capillary forces; • moisture transport by vapour diffusion; • moisture transport by liquid transport (surface diffusion and capillary flow). The equations described in this standard account for the following climatic variables: • internal and external temperature; • internal and external humidity; • solar and longwave radiation; • precipitation (normal and driving rain); • wind speed and direction. The hygrothermal equations described in this standard shall not be applied in cases where: • convection takes place through holes and cracks; • two-dimensional effects play an important part (e.g. rising damp, conditions around thermal bridges, effect of gravitational forces); • hydraulic, osmotic, electrophoretic forces are present; • daily mean temperatures in the component exceed 50 °C.