Historical Windows: Weighing Replacement vs. Rehabilitation
According to the American Institute of Architects, building renovations and adaptive reuse projects represented 47% of the design and construction market in 2011. Fenestration is a critical aspect of each of these projects, and it needs to be decided whether the building’s existing windows should be reused as-is, rehabilitated, or replaced. Hennebery Eddy Architects is currently leading the design of a $24 million rehabilitation of Strand Agriculture Hall at Oregon State University, a 100-year-old building with over 460 original wood windows. While we will talk more specifically about this project in a future post, it brought up several factors that both building owners and design teams needed to consider when deciding how to handle historical windows; including the windows’ condition, their historical merit, the quality of their materials, and their impact on energy use.
The condition of a building’s existing windows will have a large influence or whether or not the windows should be reused, rehabilitated, or replaced. The quality of their finish, glazing compound, and caulking; their operability; and the presence of any unique damage or any signs of water intrusion into the building.
If the building is designated as a historic structure or if its historical merit is particularly valued by the owner, it is likely the windows are contributing significant historical character to the building. It is often very challenging to accurately replicate this historical character in a new window without using a custom designed and fabricated product. This is often prohibitively expensive, and is sometimes just not possible.
Quality and Longevity of Materials
In the case of historical wood windows, the strength and integrity of the wood used in sash and frame components is generally far superior to wood that is used in the fabrication of modern windows. With contemporary forest management practices, new wood is harvested in much shorter cycles than it was in prior decades. Newer wood is not as dense, and thus is weaker and more prone to deterioration than the wood typically found in a historical window.
Replacement windows made of modern materials (vinyl, fiberglass, aluminum) cannot be maintained; once they fail, they need to be replaced. New windows are typically warranted by their manufacturer for 10 or 20 years. If an existing wood window has lasted 100 years, it is possible that – with proper rehabilitation and maintenance – it can last for another 100 years, or more.
Lead paint was used in most structures (including their windows) built before 1978. Asbestos was also used in many older windows, most commonly in sealants and glazing compounds. If either of these hazardous materials is present in windows that are to be rehabilitated, the abatement of these materials must be performed by a qualified and specially trained contractor. This can have a significant impact on the project’s cost/benefit analysis of window rehabilitation versus replacement. Even in the case of window replacement, these materials will require specialized disposal, resulting in an added cost to the project.
One of the primary reasons building owners consider window replacement is to improve the energy performance of their building. Theoretically, a modern-day window will almost always outperform an older window from an energy standpoint. The development of insulated glazing units, low-emissivity coatings, and thermally broken window frames has gone a long way to reduce the amount of energy that is transferred through a window assembly.
Typically, the largest amount of energy loss that occurs at windows, new or old, is through infiltration, or air leakage. In fact, most building users that express thermal discomfort are reacting to a drafty window. Air infiltration is the number one reason why old windows tend to be poor energy performers. A significant amount of energy can be saved (regardless of the performance of the window assembly itself) by properly sealing and weather stripping the window.
An oft-neglected aspect of energy conservation is the amount of embodied energy in existing and new building components. When the amount of energy it takes to make brand new windows from raw materials is taken into account, relative to the energy required to rehabilitate existing windows, the overall energy balance is very much in favor of rehabilitating existing windows.