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In 1930 Ahren was one of the designers for the Housing Exhibition of the Stockholm International Exhibition, and in 1931 he was one of the six co-authors of the Acceptera!, or Accept!, manifesto, a plea for acceptance of functionalism, standardization, and mass production as a cultural change in Sweden.
Åhrén collaborated with the sociologist, reformer and Nobel Prize winner Gunnar Myrdal from 1932 though 1935 on a social housing commission, and in 1934 they co-authored The Housing Question as a Social Planning Problem, a work that would prove influential in the structuring of the Social Democratic Swedish society, the Folkhemmet. In fact Prime Minister Per Albin Hansson, who coined the word Folkhemmet, himself moved into an Åhrén-designed functionalist house in 1936.
From 1947 through 1963 he served as Professor of City Planning for the Technical University at Stockholm.
- Student Union at the Royal Institute of Technology, 1928-1930, with Sven Markelius
- Ford Motor Company, Stockholm, 1930–31
- Flamman Soundfilm Theatre, Hornstull, Stockholm, 1930
- Terrace houses in Norra Ängby, Bromma 1931–40
- Chief City Planner for Gothenburg, 1932–1943
- Årsta centrum, Stockholm 1943–53
- Chief for the housing cooperative Riksbyggen 1943–1945