By: Elizabeth McTigue Wanga
Windows enhance the appearance of and provide a visual link between the exterior and interior of the building. Additionally, a window must be a barrier to wind, water and noise and a conduit for light and ventilation. As buildings age, their uses change, or, energy codes are enhanced, the windows on a building will need to be evaluated.
Windows should be evaluated for their significance and their physical condition. The significance of a window can be evaluated by determining if the windows are original, if they contribute the design of the building, represent a significant period or are a fine example of craftsmanship or design.
All the components of windows, frame, sash and hardware, should be evaluated during a survey to determine the best option for restoration, repair or replacement. It is helpful to create a window schedule to list the components including their condition and recommended intervention.
The following items should be included as part of the window evaluation schedule, the condition of the finish, frame, sash, glazing, hardware and weatherstripping. The condition of the paint or finish should be noted. In addition, the substrate below the paint or finish should be investigated. The location of failures should also be noted, since this can illustrate a pattern of failure.
The window schedule will illustrate the overall condition of the windows and what patterns of deterioration exist. During the process of assessing the window itself, the external factors causing the degradation should be determined and a solution should be designed to mitigate the problem. The deterioration of window components usually occurs due to the following items. First, water infiltration driven through the exterior either directly through the window or through the exterior wall surrounding the window. Second, when moisture is not naturally shed due to poorly sloped or back pitched window components. And finally, condensation on the interior of the window which stands on the horizontal components.
When there is external moisture infiltrating the window, the designer should consider the design and condition of the flashings, sealant around the windows and weatherstripping between window components. In order to shed water properly, the designer should review the pitch of sills and the drip edges to direct water away from the window.
There may also be more active active causes of degradation. Windows could fall victim to vandalism; in order to mitigate vandalism, protective glazing or mesh maybe installed over the existing window. If there are signs of insect infestation, the infestation should be eradicated prior to proceeding with repairs to the window.
For more information on evaluation of wood windows the National Parks Service Preservation Briefs and Standards are wonderful resources.