Window Retrofits

Lessons Learned from CICADA’s Preservation Working Group

When we’re asked to consider high-impact, low-intervention strategies to improve an existing buildings’ thermal performance, we always consider the windows.

Historically, windows were single glazed and constructed of either wood or steel frames, and they ultimately did not perform well. During the heating season one might have added storm windows to help with thermal comfort, but during the cooling season operable windows were essential components for cooling and ventilation so it wouldn’t matter so much if they were “leaky”. A few key things to consider when replacing existing windows are historic significance, window size, and cost.

Historic Significance

Consider whether your building is designated historic—if so, modifying the windows will likely need approval from a historic regulating agency. New windows will need to fit more closely with the look and design of the original windows, even though they won’t not necessarily need to be constructed of the same materials. Sometimes there is more flexibility to choose windows if the windows have been replaced before, but they should still fit within the character of the original building.

Photo from Kate’s Place: historic replica windows

Window Size

Window size can have a large impact of the overall energy performance on the facade as a whole. A high window-to-wall ratio (WWR) means that a building has a large amount of glazing compared to the amount of opaque wall. A high WWR limits the effectiveness of other energy retrofit options alone, such as adding insulation, to upgrade an existing building’s thermal envelope.

With preservation projects, the WWR is a component of the design we largely have no control over, and in these cases we would therefore explore windows with higher U-values that can compensate for the high WWR.

From Vasey Hall: aluminum storefront windows

Cost

A third consideration is always, of course, cost. Installing new historic replica windows can be costly and if a project still needs to follow historic guidelines, then it can be more cost effective to repair the existing windows and then look at options for interior storm windows. Interior storms are typically preferred to exterior ones for maintaining operability of the windows while preserving the original aesthetics at the facade.

Photo from Joyce’s Place: interior storm windows