In this study, we evaluated the heat and ventilation performance and verified the energy saving effects of the DSF by conducting a field survey on the environmental performance of office buildings with the DSF in cold regions. Concretely, we quantified the thermal transmittance and solar heat gain coefficient. We confirmed that the outside conditions to satisfy the natural ventilation mode (moderate season) was frequently achieved in the summer season and calculated the amount of heat removed. In addition, the energy saving effect on 10% reduction of the double-glazing with blinds on the indoor side was made a trial calculation in the DSF.