The studies listed here provide useful information for those interested in sustainability and energy efficiency as it relates to historic preservation. A listing on this page does not indicate endorsement by the National Park Service and views or opinions expressed are not necessarily those of this office.
A Search for Deep Energy Savings—This 2011 study published by the New Buildings Institute examines the rehabilitation projects of nine buildings, three of which are historic. The goal of each project was to lower the energy use of the building. Two of the historic buildings featured were also certified rehabilitations for purposes of the Historic Tax Credit Program: the Beardmore Building, Priest River, Idaho, and The Christman Building, Lansing, Michigan. Case studies on each of the projects are also available.
A Comparative Study of the Cumulative Energy Use of Historical Versus Contemporary Windows—A 2010 study by Boston professionals funded by the Boston Society of Architects. Life cycle costs were calculated and compared for a typical wood double-hung window with an added Low-E storm window and a new vinyl replacement window. Using modeling and adapting previous field studies to a Boston location, it was determined that the thermal performances of the two window systems are similar; and taking all costs into account, the historic window with a storm has a much lower life-cycle cost throughout a 100-year period. It does not seem, however, that the sources used for air leakage numbers take into account the infiltration that can occur between the window unit and the wall assembly and how that may differ between the historic window/storm and the new window.
The Effects of Energy Efficiency Treatments on Historic Windows—Published in January, 2011, by the Center for Resource Conservation in Boulder, Colorado. This study focuses on empirical testing of the energy efficiency and economy of a range of options for upgrading the energy performance of historic windows. It involved retrofitting windows in a test home in a historic district in Boulder, Colorado as well as testing in a laboratory facility developed for the study. Summary tables cover the eleven different preservation treatment options that were investigated and then compared to a new vinyl window. Most of the proposed treatments were able to outperform a new vinyl window. The study has lots of technical information and the results from both field and lab testing. While there is not a great deal of detail about the cost of the various options, there is enough cost information to provide relative payback savings.
Field Evaluation of Low-E Storm Windows— A study conducted in Chicago in 2007 by Lawrence Berkeley National Laboratory. While based on only six homes in the Chicago area, data collected from field monitoring for this study indicates a consistent benefit to using storm windows. Clear glass storm windows reduced the heating load by 13% with a 10-year simple payback. Low-e storm windows also showed an additional improvement on top of the clear glass benefits, amounting to 21% heating savings and an average payback of less than five years. Pointed out as an ancillary benefit of installing storm windows is reduced air infiltration.
Measured Winter Performance of Storm Windows—A 2002 study completed by Lawrence Berkeley National Laboratory. In testing under actual winter weather conditions, the study finds that a north-facing, wood, double-hung, single-glazed (AND intentionally leaky), sash in combination with a low-E storm window, performed very similarly to the standard low-E vinyl replacement window.
Testing the Energy Performance of Wood Windows in Cold Climates—A 1996 study which showed that window replacement will not necessarily reduce energy costs more than an upgrade utilizing the existing sash. It found that effectively sealing between the window frame and rough opening was important in reducing the infiltrative thermal losses associated with any window renovation. Storm windows, either existing or replacements, were found to be effective in reducing both infiltrative and non-infiltrative losses. This study was funded by the State of Vermont Division for Historic Preservation utilizing a grant received from the National Center for Preservation Technology and Training of the National Park Service.
Thermal Performance of Traditional Windows—Published in 2008 by Glasgow Caledonian University for Historic Scotland. This study investigated various options for reducing heat loss through windows. Among the options tested were secondary glazing systems (storm windows), insulating shades, and more traditional window treatments like shutters and curtains. Although secondary glazing was found to be the most effective option (reducing heat loss by 63%), timber shutters were also found to be effective (reducing heat loss by 51%.) Findings indicate that the most effective reductions in heat loss were attained by combining several treatments.
Window Repair and Retrofit: Studies and Research—Compiled by the California Office of Historic Preservation, these studies objectively demonstrate the viability of repairing original windows. All of the studies conclude that original window repair and other conservation strategies provide similar energy benefits of a replacement window, with less impact to the environment as an existing resource.