Performance Considerations for Historic Window Replacement and Repair

From the stained glass windows that welcome variegated light into cathedrals to the steel-framed geometric designs of Art Deco and the bold leaded glass of the Prairie style, windows have served to define the character of buildings and spaces since the advent of glazed fenestration. Not only do windows establish the aesthetics and ambiance of a structure, they form an integral part of the building enclosure. More than ornament, windows serve a vital role in protecting the building from the elements and in modulating the transfer of heat, moisture, and light from exterior to interior.

LEARNING OBJECTIVES::

• Explain the principles of window design, including energy and thermal performance, structural considerations, and building envelope integrity, as they pertain to historic and landmark window projects.
• Apply window design principles to historic window replacement projects, considering options such as insulating glazing, Low-E coatings, lamination, impact and flood resistance, security, and fire rating, while balancing performance objectives with historic integrity.
• Differentiate among the various types of window testing, from manufacturer qualification testing to off-site performance and visual mock-up testing to field tests of installed fenestration, and describe how each is used to evaluate the proposed window assembly.
• Identify the challenges to restoring historically significant, irreplaceable windows and the ways in which historic materials may be treated and maintained to address condensation, energy performance, leaks, operability, and other considerations.