An opposite sunspaces passive solar air heating system has been developed to provide passive solar heating in multistorey buildings. The system envisages the natural transfer of the solar energy gained in the southern sunspace of an apartment to the northern glazed space through air ducts placed in the ceiling and Boor. The heated air in the southern sunspace rises, enters the air ducts placed in the ceiling and Bows through these ducts to the northern glazed space, while the displaced air in the southern sunspace is replaced with cooler air flowing from the northern glazed space to the southern sunspace through the air ducts placed in the floor. As the system may be applied to eastern and western sunspaces as well as to south and north, the constraint of orientation of the building with respect to the sun is reduced. In Ankara Solar House, which simulates an apartment of a multistorey building, the system is applied between the southern and northern Facades. The internal Boor area of the house is 100 m(2). Both the southern and northern facades are completely covered by glazed spaces. The roof, floor and walls on the east and west are heavily insulated to simulate an intermediate apartment in a multistorey building. The construction of Ankara Solar House was completed in January 1993. In this house, the natural air circulation travels a distance of 10 m between the southern sunspace and the northern glazed space. In Belko Solar Building, the system was applied between the eastern and western sunspaces. Before noon, solar energy gained in the eastern sunspace is transferred to the west and vice versa in the afternoon. The building is designed to have two storeys with 1000 m(2) usage area. The construction of Belko Solar Building was completed in December 1993. In this building, the natural air circulation travels a distance of 13 m between the eastern and western sunspaces.