 His larger commissions included the Country Press Association Building at the corner of Elizabeth and Edward Streets (1924-25 - demolished); Heindorff's Building in Queen Street (1926-28 - demolished); Inchcolm Professional Chambers on Wickham Terrace (1929–30); and the new Surfers Paradise Hotel (1936-37 - demolished).Trewern was actively involved in furthering professional architectural standards in Queensland.He served as Vice-President of the Queensland Institute of Architects 1929–30, Member Board of Architects of Queensland 1929–35, Fellow of the Royal Australian Institute of Architects 1930, President Queensland Institute of Architects 1931–35, Fellow of the Royal Institute of British Architects 1931; Vice-President of the Royal Australian Institute of Architects 1932–33, and Federal Councillor 1932–35.