The objective of this project was to assess the service life and life cycle environmental performance of the main variants of window system used in the Australian market. The project compares timber framed windows (and aluminium-skinned timber framed windows) with their major competitors in the market. In order to assess the window systems, 51 archetypical window specifications were chosen, with the help of a Project Advisory Group to represent the range of window types and variants used in the market. These archetypes were then studied in detail for their maintenance, durability, service life and hence full life cycle environmental impacts.
Initial embodied, life cycle embodied and operational energy implications are all assessed using Life Cycle Assessment (LCA). The LCA results were interpreted by characterisation, normalisation and weighting. Characterisation used the CML 2000 protocol and the results were then normalised against the annual impacts estimated for an average Australian citizen. Finally the results were weighted using data compiled from international sources and adapted in line with the Green Building Council of Australia’s weighting values for different Australian States and Territories, to bring the results to a single ecopoint value. Results are presented for embodied ecopoints and embodied CO2-E.
In contrast to similar work conducted in other countries (mostly in Europe), the embodied impacts prove to be dominant to the life cycle assessment of the windows in areas where the climate is very mild and only minimal heating or cooling are required. Only in Northern Territories are the cooling loads in buildings high enough to justify the additional embodied impacts for double glazed windows. Under heating conditions though, double glazed windows are justified in all States and Territories except Northern Territories and Queensland. Under combined heating and cooling conditions, fully air-conditioned buildings for example, double glazed windows are justified in all States and Territories except Queensland and Western Australia.
Window size is the most significant factor in life cycle impact, double or single glazed is next most important, frame type next and window style next. Other factors are not so significant. Overall, aluminium skinned timber framed windows perform best, hardwood timber framed windows next, PVC next and aluminium worst. The biggest differences occur in harsher climates for either heating or cooling. In milder climates, where double glazing is not justified, the frame becomes the main differentiating factor.
The report identifies messages that differentiate aluminium skinned timber and hardwood timber framed windows that can be promoted to the Australian market, but recommends caution given some gaps and uncertainties in the LCA data and assumptions.
The report identifies research and innovation opportunities for the industry to improve the reliability of these results and to further enhance the environmental performance of timber framed windows
- Comparative Service Life Assessment of Window Systems for the Forest and Wood Product Research and Development Corporation, by Nigel Howard, John Burgess and Charles Lim, ISSN: 0113-3675, 2007.