Historic Windows

Windows are important elements in establishing the character of buildings. Unfortunately, the ease with which windows can be replaced makes them one of the most vulnerable parts of a building.

Inappropriate replacement with different materials or changes in the window style can destroy or diminish a building’s historic character.


The repair of wood windows is more practical than most people realize and retaining the original windows and their related trim adds to the value of a property.

The Secretary of the Interior’s Standards for Rehabilitation, the basic guide to rehabilitation followed by the Historic Preservation Board, calls for respecting the significance of original materials and features, repairing and retaining them whenever possible, and when necessary, replacing them in kind.

Typically, historic windows consist of muntins, sash, frames, and molding which have a molded relief.

In a new window, the profiles of these elements are typically flatter and wider, or conversely, narrower and thinner, than the historic profiles. For example, the muntins in a new double-glazed window may be much wider and flatter than the existing muntins. Even though the new window may duplicate the number of existing window panes, the character of the historic window is lost because of the change in relief. This, in turn, diminishes the overall historic character of the building.

Window deterioration can be due to several factors: poor design, moisture, vandalism, insects, and lack of maintenance. Moisture is the primary contributing factor in wooden window decay. Joints and seams should be inspected and caulked to eliminate the problem. The glazing putty should be checked for cracked, loose or missing sections which allows water to saturate the wood. The putty on the interior side of the pane should also be inspected, because it creates a seal which prevents condensation from running down into the joinery. Paint failure is often a clue to areas of excessive moisture.

In the majority of cases, the decision to replace wood windows is erroneously based on the condition of the sills and not the rest of the window frames. Decayed wood sills can be waterproofed, patched, built-up, consolidated, and then painted to achieve a sound condition, good appearance, and greatly extended life. Deteriorated parts of a window frame can be replaced with new matching pieces, or new wood spliced to existing members. Most millwork firms can duplicate muntins, bottom rails, or sills, which can then be incorporated into the existing window. If damage is extensive, it may be more practical to purchase new sashes which can be installed into the existing frames. A replacement window should retain as much of the character of the historic window as possible.

Windows should not be replaced unless absolutely necessary.
Traditional wood, double hung windows can often be easily repaired with standard parts carried by local hardware stores. The required labor can often be provided by the homeowner or a handyman/carpenter. Once repaired, these windows can offer many additional years of use.

Replacement is often more costly than repairs.
New windows will usually cost significantly more than maintenance and repair work.

Wood windows are energy efficient..
Wood is a significantly better insulator than metal, plastic or vinyl.

Before considering the replacement of wood windows in historic properties, the Historic Preservation Staff will undertake a thorough Window Condition Assessment. This will involve an on-site visit to look at each window and document with photographs. When windows are boarded over, the boards must be removed in order to preform the assessment.

Please contact the Historic Preservation Division, at (561) 822-1435, if you have questions about historic windows.