In 2003, the Building Code of Australia (BCA) introduced thermal performance requirements for residential buildings. While the introduction of thermal performance requirements to new housing has an immediate impact on energy that may be used for heating or cooling, this has no effect on existing housing. It is estimated that less than 2% of the housing stock is replaced each year. Methods to improve the heating efficiency of existing housing include the addition of double glazing and roofing, wall and sub floor insulation. The latter two often receive little attention due to the difficulties that may be experienced. The glazing in existing houses affects both the insulation value and infiltration rates of external walls. Many house owners are advised to remove the existing timber windows and replace them with double glazed aluminium windows. The windows are often in a reasonable state of repair but they simply become landfill. Aside from the environmental cost of replacing existing windows, there is also the financial burden. With these issues in mind three test boxes have been constructed at the School of Architecture in Launceston. The test boxes are made from polystyrene and have a window inserted in the northern wall. The windows consist of an existing single glazed control window and two retrofitted double glazed systems. Measurements are being taken to examine temperature and humidity differences between the three window types. The retrofitting systems adopted have been chosen based on the limited skill level of most house owners.