Replacement versus retrofits? Weatherstripping versus storm windows? As preservationists you are probably confronted with questions, derision, and downright disbelief when you try to make the case for reusing existing windows. Happily, a new report just released by the Preservation Green Lab is sure to change the nature of the debate and make your advocacy a little easier.
This 59-page report, Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement, was released today and is available on www.preservationnation.org/greenlab. It was funded by the National Center for Preservation Technology and Training and conducted in partnership with Cascadia, the leading green building organization in the Pacific Northwest, and Ecotope, an engineering firm which specializes in energy and resource conservation in the built environment.
Researchers set out to determine the potential energy savings related to common practices for upgrading older, existing single-pane residential windows. Variables such as climate, regional energy costs, heating system efficiency, and window system performance were evaluated to understand which options provide the greatest energy savings for homeowners.
Researchers looked at five cities, Portland, Boston, Chicago, Atlanta, and Phoenix, and researched the following retrofit scenarios:
- Weather stripping for existing window
- Exterior storm window
- Interior window panel
- Insulating cellular shade
- Combination of exterior storm window and insulating cellular shade
- Interior surface film (including weather stripping)
- New, high performance replacement window
Patrice Frey, director of sustainability for the National Trust notes that in undertaking this study, the study team wasn’t sure what they would find. She notes that the Green Lab staff “were warned by our study partners that the results may be disappointing to preservationists and suggest that window replacement offers a sizable advantage over window reuse and retrofit.” The results, however, conclude that a number of existing window retrofit strategies come very close to the energy performance of high-performance replacement windows at a fraction of the cost.
Specifically, the report finds:
Retrofit Measures Can Achieve Performance Results Comparable to New Replacement Windows. When the performance for each upgrade option is taken into account, this study shows that there are readily available retrofit measures that can achieve energy savings close to new, high performance replacement windows.
Almost Every Retrofit Option Offers a Better Return on Investment than Replacement Windows. Findings from the cost analysis showed that new, high performance windows are by far the most expensive measure, costing at least double that of common retrofit options when considering materials, installation and general construction commonly required for an existing home. In all climate zones analyzed, cellular shades, interior storm panels and various exterior storm window configurations offer a higher average return on investment compared to new, efficient replacement windows.
The Bottom Line. Retrofitting windows with high performance enhancements can result in substantial energy savings across a variety of climate zones. Selecting options that retain and retrofit existing windows are the most cost effective way to achieve these energy savings and to lower a home’s carbon footprint. Retrofits extend the life of existing windows, avoid production of new materials, reduce waste and preserve a home’s character.
Note to Forum Members: Keep your eyes peeled for a Forum Focus white paper on this report later this month.
Also check out PreservationNation’s [10 on Tuesday] 10 Things You Should Know About Retrofitting Historic Windows