Windows tend to be a "flash point" in the dialogue between green building advocates and preservationists, with preservationists preferring to retain character-defining windows, and green building advocates often arguing that it is necessary to replace windows to improve energy performance. It's safe to say that the National Trust gets more questions about this issue than any other related to the Sustainability Initiative, and we receive many requests for step-by-step technical assistance for greening historic windows. Our new Tip Sheet for Historic Wood Windows addresses many of these questions. The tip sheet, which was prepared by Rebecca Williams of the Northeast Office, explores the environmental benefits of retaining wood windows and offers suggestions for greening windows.
Interestingly, data from the U.S. Dept. of Energy finds that windows usually account for about 10% of energy loss in buildings, while walls, ceilings, and floors account for 31% of thermal loss. And as Barbara Campagna and I have mentioned in previous blog entries, studies have demonstrated that properly weatherized historic windows perform about as well as new, thermally resistant windows. Nevertheless, there continues to be concern about the issue of windows, and the widespread perception that going green automatically requires replacing windows.
The Windows Tips Sheet is really just the beginning of our work on the issue. Because this topic is so important, we’ve established a comprehensive Historic Windows Assessment Project to study windows more comprehensively. Thanks to partial funding from the National Center for Preservation Training and Technology, the first phase of our Historic Windows Assessment Project will compare historic windows to the latest in green technology and create a "decision matrix" to help building owners decide the most appropriate path to improving their windows. The research will be undertaken with scientists from the Lawrence Berkeley National Laboratory in California.
The second phase of the research will look at windows in the context of thermal loss in the entire building to help demonstrate the importance of looking at buildings holistically, rather than focusing on one source of thermal loss. The third phase will look at the total life cycle impacts associated with replacing rather than reusing an existing window. In other words, instead of just looking at energy saved through operation of a new window, this study will look at the environmental costs of manufacturing new windows and replacing them periodically since they typically cannot be repaired.
In the meantime, have a look at the Tip Sheet, and tell us what you think!