The performance of the heating system of the house described in this paper was monitored from December 1978 until June 1980 by the Solar Group of The Federal Institute of Technology in Lausanne, which is working on Task I of the International Energy Agency. The performance of the house, in the local climate, was assessed from the data measurements which were then used in a second step to validate the behaviour simulation of a direct-gain solar system. The aim of this project is to develop a new kind of architecture for low-energy housing for Switzerland.