A report produced by the Preservation Green Lab, a project of the National Trust for Historic Preservation, offers insight for homeowners weighing the financial and energy tradeoffs between replacing or repairing older, less efficient windows. This analysis, Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement, builds on previous research by examining multiple window improvement options, comparing them to replacement windows across multiple climate regions.

This report, made possible through the generous funding of the National Center for Preservation Training and Technology, concludes 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. Saving Windows, Saving Money’s key findings offer homeowners, contractors, architects and others with compelling evidence of the merits of retrofitting windows as opposed to outright replacement.

The key findings include:

• 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.

Study Partners

• Cascadia Green Building Council
• Ecotope

With Support From

• National Center for Preservation Technology and Training