Why Restore Wooden Windows?

Anyone owning an older home with wooden windows knows they can be a source of discomfort if not maintained. Drafts, sash painted shut, broken sash cords, missing hardware, and rotted sills can be problems with older windows. Before spending thousands to replace deficient windows, building owners should happily consider the many advantages of restoring and maintaining them.

Aesthetics. The design of the original windows looks best with the building. The original profiles of the sash, trim, and window elements were designed to complement the rest of the building. New windows will never have the nuances of the old ones. Restoring windows also preserves the authenticity of the building. Once original materials are gone, they are gone forever.


Changes to the original windows and entry doors significantly alters this building’s appearance.

Property Values. No one will make the argument that poorly maintained windows will enhance a building’s value. On the other hand, they can be a real impediment when it comes time to sell. Original windows, if well maintained, can actually improve the sales potential. The value of old windows was summed up by the Deadwood, SD, Historic Preservation Officer when talking about a Deadwood Rec Center window upgrade project this way: “There’s a saying that goes, ‘They’re not old because they’re old, they’re old because they’re good….The original windows from 1912 are only being refurbished. With proper maintenance and care they can last longer than the replacements…It’s the 20 year-old replacement windows that are being replaced.’” 1

Material Quality. Wood windows installed before the mid 20th century were built with “old growth” lumber. The wood was harvested from virgin forests where it grew slowly, and it has tighter cell structure and denser rings than today’s farm raised wood. Old growth wood is also more disease resistant. This is important because the denser the wood and tighter the cell structure, the more difficult it is for water to wick through the fibers causing the wood to rot.


Old (top) vs. New (bottom) Growth Pine.

Energy Efficiency. One of the biggest arguments for replacing old windows has been the notion that new windows are more energy efficient and therefore result in saving money on energy bills. In recent years, this idea has been tested in a number of important studies and found to be wanting. In a major study conducted by the Preservation Green Lab of the National Trust for Historic Preservation and funded by the Department of Interior, National Park Service, multiple window improvement options were analyzed for multiple climate regions (Portland, Boston, Chicago, Atlanta, Phoenix). The study compared relative energy, carbon, and cost savings for the options. The results of the analysis demonstrated that a number of existing window retrofit strategies come very close to the energy performance of high-performance replacement windows and at a fraction of the cost. The strategies included weather stripping, interior surface film plus weather-stripping, insulating cellular shades, exterior storm windows, and interior window panels. The study concludes that upgrading windows (specifically older, single-pane models) with high-performance enhancements can result in substantial energy savings across a variety of climate zones. Selecting options that retain and retrofit existing windows is the most cost-effective way to achieve energy savings and lower a home’s carbon footprint.2

In another study conducted at the University of Illinois, Champagne-Urbana, for the Capital Development Board, window treatments for Lincoln Hall, a century old academic building with 433 windows, were evaluated for operational cost, specifically, the cost to heat and cool air around the window. The window types evaluated were: 1) unrestored window with new storm window from manufacturer “A”; 2) unrestored window with new storm window from manufacturer “B”; 3) new replacement window matching design of original window; 4) restored window with weather stripping and hermetically sealed double glazed glass. The study demonstrated that there were no significant operational cost differences between restoring existing windows with a storm window or insulated glass and replacing the windows. The study also calculated maintenance costs of the above window types over 50 years, and found no significant difference in maintenance costs except for washing both sides of the storm windows.3

Environmental Impact. It has been estimated that land-fills contain 40 to 60 percent architectural waste. Each year, Americans demolish 200,000 buildings. That is 124 million tons of debris, or enough waste to construct a wall 30 feet high and 30 feet thick around the entire U.S. coastline!4 Restoring windows keeps them out of landfills.

Preserving old windows conserves embodied energy, the sum total of the energy required to extract raw materials, manufacture, transport, and install building products. It also eliminates the need to expend the same kinds of energy replacing windows.5

Maintenance. The good news about old wood windows is that they can be repaired. This is not the case with “maintenance free” windows. This is because maintenance free windows cannot be repaired. For example, when seals on insulated glass in replacement windows fail, the unit must be replaced, it cannot be repaired. Old wooden windows can be reglazed and broken panes can be replaced.

Products and tools for restoring virtually all wooden window elements are available in paint and hardware stores. Even windowsills and sash that could be pulled apart by hand, can be saved. Epoxy wood consolidants and wood replacement compounds are available to restore the strength of rotted sections and replace missing sections of wood. Epoxy consolidants are two-part liquid compounds that penetrate and harden rotted wood. The liquid wicks through the hollow wood fibers and replaces missing lignin. A consolidant with some flexibility when it hardens will expand and contract with the wood and not make it brittle. It also helps to make a good transition between sound wood and epoxy patching compound. Epoxy wood replacement compounds are virtually shrink-free and bond tenaciously to wood. They can be sanded, routed and finished like wood. In fact, repairs of even the most rotted wood can be invisible.


Simple epoxy repairs restore this window to its original beauty.

Many other products are used for restoration. Boron-based wood preservatives will help prevent the growth of decay organisms should moisture cause them to become active. Paint removers, scrapers, 3-in-1 tools, putty knives, sandpaper and sanders, glazing compound and glazing points, glass, particle masks and respirators, good quality cotton sash cord and sash chain, heat guns, paint, primer, and paint brushes, disposable gloves, latches and lifters, sealants and weather stripping, plastic sheeting, safety glasses, drills and bits, wooden dowels, are all part of the mix.

Homeowners can restore their own windows or hire painters and contractors to make the repairs. The important points are these: 1) window restoration can proceed regardless of the size of one’s bank account; 2) restored windows can be highly energy efficient; and 3) older buildings can look more beautiful than ever because they have the original details plus the patina of age.

Marsha Caporaso, President


Kenosha, Wisconsin

  1. Pearson, Jaci, “Rec Center Window Upgrade to Cost $141 K”, Black Hills Pioneer, Nov. 15, 2013.
  2. “Saving Windows, Saving Money: Evaluating the Energy Performance of Window Replacement and Retrofit”, Preservation Green Lab of the National Trust for Historic Preservation, 2012.
  3. Bailey Edwards Architecture and OWP/P, “Lincoln Hall Windows Research Report”, Dec. 30, 2008, Revised June 4, 2009.
  4. Hadley, James, “The Home of the Future?”, Architecture Boston, 10, No. 2, March/April 2007, 44-47.
  5. Sedovic, Walter and Gotthelf, Jill, “What Replacement Windows Can’t Replace: the Real Cost of Removing Historic Windows”, APT Bulletin: Journal of Preservation Technology, 36; 4, 2005, 25.