Extension to an Existing Dwelling Thornbury. This single fronted house in an ideally located street in Thornbury was ready for renovation when the owners of this property purchased the house. Retention of the heritage front and simple removal of the rear addition ensured that the streetscape was retained and the house was then upgraded to contemporary standards. Retaining and renovating existing buildings is a sustainable construction approach as it reduces the embodied energy used, and therefore the carbon produced, during construction.