What Does the Research Say?

Studies have shown that retaining and retrofitting existing heritage windows is “the most cost effective way to achieve energy savings and to lower a home’s carbon footprint.”[1]

Saving Windows, Saving Money, concluded that “there are readily-available retrofit measures that can achieve energy savings within the range of savings expected from new, high performance replacement windows.”[2] In fact, the study found that in Northern American cities such as Minneapolis, Boston, and Anchorage, a retrofitted double -hung window with a single-glazed storm window will out-perform new vinyl windows.[3]

The study concludes that “almost every retrofit option offers a better return on investment than replacement windows….This challenges the common assumption that replacement windows provide the greatest benefit to homeowners.”[4] Homeowners and design professionals often make decisions about upgrading windows “without a clear understanding of the options available….or proper consideration of” the historic value of the existing windows.[5]

The Effects of Energy Efficiency Treatments on Historic Windows similarly agreed, stating that the “most important conclusion flowing from this research is that it is possible to improve the overall energy performance of existing window systems by well over four fold through repairs and sealing plus the installation of an excellent storm window without altering their historic character….old windows can be saved while raising the overall efficiency of a home, improving its comfort, and retaining it’s aesthetic charm.”[6]

Studies also stress that the environmental impact of the production of replacement windows and their eventual disposal should be considered when making comparisons. Of particular concern is the wide use of vinyl (PVC) [7] in new window production, and the risks posed to human health and to the environment over the course of its life cycle.

Contrary to what you may have heard from the building, design and energy industries, therefore, new windows are not the inherently better choice when compared to the retention of your historic windows. And they will not save you money, because the money you may save in energy costs will never be recouped before you have come close to paying for them, and have to discard and replace those windows—again.

Mathew Cummings, an architect based in Massachusetts who works on contemporary buildings as well as some of his country’s oldest houses, is unequivocal on the subject: "Never, never, never throw away old windows.”[8]

[1]National Trust for Historic Preservation, Preservation Green Lab, Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement, 2012. p. IV. See also Testing the Energy Performance of Wood Windows in Cold Climates, A Report to the State of Vermont Division for Historic Preservation, Agency of Commerce and Community Development, August 1996.

[2]Ibid., p. 46.

[3]Ibid. See graphs, p. 4-3 and 4-4.

[4]Ibid., p. IV.

[5]Ibid., p. III.

[6]Center for Resource Conservation, The Effects of Energy Efficiency Treatments on Historic Windows, January 2011, p. 4-16.

[7] PVG. Akovali, Plastic materials: Polyvinyl chloride (PVC), in Toxicity of Building Materials, ed. F. Pacheco-Torgal,

S. Jalali and A. Fucic, Woodhead Publishing Series in Civil and Structural Engineering, 2012, pp. 23–53.

[8]Quoted in Cole, Regina, Forbes, “Don’t Buy Replacement Windows For Your Old House,” July 17, 2018.