Replacement of historic wooden windows has become a thriving industry. Windows are blamed for energy loss and the replacements are marketed and sold as an efficient alternative. However, the facts are something else. Only 10 to 20% of a building’s energy loss actually comes from windows. And most of the energy loss associated with windows is due to cold/heat infiltration at seals, not through glass. The replacement may not be cost effective at all when compared to the actual energy savings costs.

Historic windows have been on the job for 50 to 100 years and can continue to last indefinitely when properly maintained, weather-stripped, and/or combined with a storm window. Replacement windows are plastic vinyl, aluminum or a composite. None will last as long as the original window. In fact, a replacement window will often have to be replaced within 10 to 15 years.

Windows are always a character defining feature of an historic building. When considering whether or not a replacement window is appropriate first individually assess the condition of each window including the following window components: sash, muntins, sill, frame, glass, operational hardware, and fittings. If one or more of these components are in disrepair, consider and address the possible causes: poor design, moisture infiltration, vandalism, lack of maintenance, or insects.

Most historic wood windows are made of old growth, extremely durable hard woods and their craftsmanship allows for easy repair. Repair should always be considered the preferred option. If a window can not be repaired it should be replaced in-kind ensuring that the new window is appropriate and matches the original materials and characteristics.

Learn more about about historic window preservation:

• Historic Windows Workshop (ppt)
• Historic Wood Windows Tips (pdf)