Recently, building envelopes with efficient insulation of low thermal conductivity, including light building envelope, which allow to increase thermal protection of buildings, are widely used. This new building envelope require a comprehensive study, because previously considered unimportant features often start to make significant effect on the performance characteristics of structures. To reduce the air permeability in the constructions wind-proof membranes are used. However, the influence of air filtering in such structures has not been researched yet. When the air-permeable building envelopes are used, the heat flow is moved away also due to the air filtering. It is proposed to take into account the convective heat transfer mechanism commensurate with the conductive heat transfer mechanism. In the formula for determining the heat flow due to the air filtering the filtration coefficient of air through the building envelope is used. This coefficient is found experimentally for light building envelopes. Furthermore, the empirical expression for the filtration coefficient, which relates it and the coefficient of heat loss is found.