The company was founded in 1953 in Montréal. A partnership between three McGill University School of Architecture graduates - Raymond Tait Affleck (1922-1989), Guy Desbarats (1925-2003) and Jean Michaud (1919-1995) - and two McGill architecture professors - Fred David Lebensold (1917-1985) and, joining in 1954, Hazen Edward Sise (1906-1974). and Dimitri Dimakopoulos (1929-1995), another McGill School of Architecture graduate, began working with the group. D. Dimakopoulos became a full partner in 1957. Following the departure of Jean Michaud in 1959, the firm became Affleck, Desbarats, Dimakopoulos, Lebensold, Sise (ADDLS) for the next decade. In 1968, Hazen Sise retired, Dimitri Dimakopoulos left to open his own office, and Guy Desbarats departed to found and head the University of Montréal's Faculté de l'aménagement. In 1970, Ray Affleck, Fred Lebensold and Arthur Boyd Nichol (who had been an associate in the previous firm since 1956) regrouped and founded ARCOP Associates; designed churches, municipal and provincial government buildings, exhibition pavilions, multiple-dwelling residential buildings, cultural buildings, commercial and industrial buildings, and educational buildings.