Later in the 1940's, Koch designed several affordable prefabricated housing prototypes. He did the original Acorn House (1946), re-design of the all-steel Lustron House (1949), and Conantum, one of the nation's first cluster housing developments, in Concord MA (1951). Launched in 1953, his Techbuilt House was wildly successful and would eventually be available in twenty-two models. Over 3,000 houses were sold in the US before 1963. In 1958, Koch co-authored a book with Andy Lewis titled At Home With Tomorrow about the Techbuilt House and his other prefab designs.