Window Replacement Regulation | HPC Training | Wisconsin Historical Society

Guide or Instruction

Window Replacement Guidelines

Chapter 8: Preservation Commission Design Guidelines, Page 6 of 8

Window Replacement Regulation | HPC Training | Wisconsin Historical Society

Preservationists face a multimillion-dollar industry promoting the replacement of historic wood windows with new windows made of vinyl, vinyl clad, or aluminum. Commission members should become familiar with several studies showing that, under most circumstances, the removal of original wood windows to replace them with vinyl is simply not warranted.

By keeping an original window and adding a good interior or exterior storm window, property owners can achieve as much thermal efficiency as with most replacement windows.

Making a Case for Historic Wood Windows

Property owners often think they need new windows to improve the energy efficiency of their home. Common comments include:

  • "I can't afford the energy loss from my old, drafty windows."
  • "My old windows are too expensive to repair."
  • "I need the energy savings from new windows."

However, many property owners do not realize that the great majority of heat loss in houses is through the attic or uninsulated walls, not through windows.

Benefits of Saving Original Wood Windows

Commission members can tout the following benefits of saving original wood windows:

  • Properly repaired historic windows with storm windows have an R-factor similar to most new windows.
  • Historic wood windows have life expectancies of 60 to 100 years, while warranties for most new vinyl and aluminum windows only guarantee them for eight to ten years.
  • Despite manufacturers' warranties, 30 percent of the windows being replaced today are less than ten years old.
  • Insulated glass seals in vinyl windows have a tendency to fail in two to six years.
  • New wood windows are made with new growth lumber that is not as strong or rot resistant as the old growth lumber used in windows from pre-1960 houses.
  • Preserving historic windows conserves their embodied energy and eliminates the need to spend energy on replacement windows.
Studies that Support Historic Window Repair

The studies listed below support window repair rather than replacement:

Creating Windows of Energy Savings Opportunity
Home Energy Magazine, 1997. This Vermont study found that the cost of replacing historic wood windows with new windows provided only a minimal savings.
What Replacement Windows Can't Replace: The Real Cost of Removing Historic Windows
Journal of Preservation Technology, 2005. This study examined the environmental and conservation costs of replacing historic wood windows with vinyl and aluminum materials.
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 (1996-08). Available from the National Center for Preservation Training and Technology. The key conclusions of this report include:

  • Window upgrades that use the existing sash can achieve performance indistinguishable from the replacement sash. The economics of the upgrade depend on the leakiness of the original window.
  • It is often cost-effective to address air leakage from a loose existing window. The report discusses fixing air leakage between the window and rough opening as well as between an exterior storm window and the trim.
  • It is worthwhile to consider installing a second layer in windows that have a single pane of glass. Options include installing storm windows, replacing the glass with insulated glass units, and using low-emissivity (low-E) glass.