[4] He soon decided to stay, and his first business venture was Brummels Gallery in South Yarra, which focussed on contemporary Modernist Australian painting, sculpture and prints.
[9] The success of this venture led to him being approached to part own, develop and operate another in Merimbula, NSW, The Black Dolphin, which opened in 1961, and was designed by noted modernist architect and critic Robin Boyd.
[7] The project architect was a young Graeme Gunn, and the use of undressed tree-trunk posts, natural finishes, and native planting was an early example of the bush aesthetic in Australian architecture.
[11][12][13] In 1969 the firm's first foray into larger concerns was the Elliston Estate in Rosanna,[14] where a sense of flowing native landscape on an existing subdivision was created, and a range of house designs by four architects – Charles Duncan, Daryl Jackson & Evan Walker, McGlashan Everist and Graeme Gunn.
[16] Winter Park led the Victorian Government to introduce the Cluster Titles Act 1974,[4] and in 1975 it received a citation in the Royal Australian Institute of Architect's Housing Awards.
[15] In 1968, Yencken commissioned Gunn to design a holiday house called Baronda, in what is now Nelson Lagoon Mimosa Rocks National Park in NSW, created in part by his gift of the property to the state in 1973.
[5] Yencken also founded the planning and landscape architect firm Tract Consultants, around the same time, holding positions of Chairman and Managing Director between 1971 and 79.
[19] Yencken was then appointed Chairman of the Interim Committee on the National Estate, which led to the formation of the Australian Heritage Commission which he then chaired from 1975–1981, with their first meeting on 27 July 1976.
[20] The main work of the Commission was the creation of the Register of the National Estate, a comprehensive overview of the Australian heritage places, which had more than 13,000 listings when it abolished by the Howard government in 2004.