The thermal and hydrodynamical characteristics of an externally insulated building with a vent layer were investigated numerically and empirically to verify the possibility of the thermal controllability. It was shown clearly that the room temperature can be controlled not only by the existence of the vent layer but also by the compulsory ventilation. Since solar radiation is strong in summer, the use of the vent layer as a further cooling function is possible by keeping the vent layer open. In addition, it is possible to intercept the rise of room temperature by operating the opening-and-closing valves attached at the inlet and outlet of the vent layer so that the heat is not transported to the interior on summer nights when the outside temperature is high. On the other hand, in winter, the energy burden needed for the maintenance of a comfortable indoor environment can be reduced by closing the vent layer.