His graduation project was a design for the Enge station in Zurich, developed along with fellow students Flora Crawford and Rudolf Steiger.
[1] In 1928, Haefeli and 28 prominent European architects of the time formed the Congrès Internationaux d'Architecture Moderne (CIAM) in La Sarraz, Switzerland.
The co-founders included Le Corbusier, Sigfried Giedion, Hendrik Berlage, Karl Moser, and his future business partner Werner M.
[1][2][4] From 1938 – 1939, Haefeli, Werner Moser, and garden architect Gustav Ammann designed the Allenmoos open-air swimming pool in Zurich (dubbed Parkbad).
[4] He contributed numerous furniture pieces to Wohnbedarf AG, a showroom run by Werner Moser, Rudolf Graber, and Sigfried Giedion from 1931 onwards.