PURPOSE: To promote habitability by designing a roof, external wall window of an existing house as a heat-insulating structure and, at the same time, making it possible to open and close ventilators, and providing a heat exchanger and a duct leading under the floor to an attic to air-condition the house entirely.

CONSTITUTION: A plastic form plate 17 is stuck on an existing attic, a dry type external walling 21 is mounted to the external wall, a window is a double sash 23 as a heat-insulating structure and, at the same time, opening and closing valves are mounted to ventilators, 5a, 6a, etc. A heat-exchanger 24 is mounted to the attic and, at the same time, a duct 25 leading to a space under the floor its provided and, at the same time, an air-conditioner 34, etc., are installed, and a temperature, humidity, opening and closing valves of ventilators, etc., are entirely controlled by a controller 33. According to the constitution, a comfortable house can be obtained.