This Standard specifies the method of calculation of the thermal resistance and thermal transmittance of building components and building elements, excluding doors, windows and other glazed units, components which involve heat transfer to the ground, and components through which air is designed to permeate.The calculation method is based on the appropriate design thermal conductivities or design thermal resistances of the materials and products involved.The method applies to components and elements consisting of thermally homogeneous layers (which can include air layers). The standard also gives an approximate method that can be used for inhomogeneous layers, except cases where an insulating layer is bridged by metal.