It analyzes decades of research about the performance of double hung windows, comparing the relative energy, carbon and cost savings of various choices in multiple cities across the United States. The report concludes that upgrading windows (specifically older, single-pane models) with exterior storm windows and insulating shades can result in substantial energy savings across a variety of climate zones.
“A number of existing window retrofit strategies come very close to delivering the energy benefits of high-performance replacement windows – at a fraction of the cost,” said Mark Huppert, technical director of the Preservation Green Lab. “From weather stripping and sealing, to installing exterior storm windows or interior cellular shades, almost every retrofit option offers a better return on investment than outright replacement.”
These findings have important environmental and economic ramifications for consumers. Residential buildings are responsible for approximately 20 percent of total U.S. energy use and carbon dioxide emissions. Many of these buildings are single-family homes where heating and cooling represents the largest uses of energy, and where windows are an important factor in home energy efficiency. Americans spend over $17 billion annually on heating and cooling.
“Homeowners and designers who want to upgrade existing windows have many choices: from simple low cost, do-it-yourself solutions to complete replacement, which can cost tens of thousands of dollars,” said David J. Brown, executive vice president and chief preservation officer of the National Trust. “This report provides the context and data to help budget conscious consumers make sound decisions.”
“Whether you live in Boston, Chicago or Phoenix, the conclusions are nearly identical,” said Kirk Cordell, the executive director of the National Center for Preservation Training and Technology. “With careful planning, it’s possible to affordably increase the energy efficiency of a home or residential building without compromising its design quality or historic character.”
Research support for the study was provided by Cascadia Green Building Council and Ecotope, a consultancy focused on energy efficiency and sustainability.
About the Preservation Green Lab
The Preservation Green Lab is a sustainability think tank and national leader in efforts to advance the reuse and retrofit of older and historic buildings. A project of the National Trust for Historic Preservation, the Green Lab was launched in 2009 and is based in Seattle, Wash. Learn more at: www.preservationnation.org/greenlab
This research was made possible through Grant MT-2210-08-NC-01 from the National Center for Preservation Technology and Training (NCPTT).