Historic Wooden Window
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Engineering calculations for the combination of a storm window and a wood window is better than normal insulated glass. The newer high performance glass energy savings are so small that an engineering energy-use and expenditure calculation indicates that new windows are an extremely bad investment savings compared with a combined wood and storm window. It takes 240 years for payback on a low-e replacement window and about 40 years to recoup the cost of standard replacement windows. Those payback years do not take into account the considerable amount of energy to make, deliver and install new windows and transport the old windows to the landfill. In addition, new windows also have many more constituent parts that are likely to fail resulting in operation that deteriorates with age. It also becomes increasingly difficult to find replacement parts as the windows age, but glass, glazing, and sash cord; the basic necessities for rehabilitating historic wooden windows will always be available. Finally, the old-growth heartwood that historic windows were manufactured with has a far greater lasting capacity than new second growth timber due to a number of reasons including density and resin content.
As mentioned earlier, there are a number of options available for increasing energy efficiency, and when applied simultaneously, these methods can increase the overall efficiency of historic wooden windows dramatically. For example, much of the heat loss and air leakage involving historic wooden windows results from the hollow, un-insulated space created for the window weights on either side of the window sashes. However, replacing the window weights with spring-loaded window tape balances will eliminate the need for the weights thus allowing for the installation of insulating material in the now vacant sash boxes.
It is also possible to rout grooves in the meeting rails of the sashes and install RST Corporation’s WS87 offset plastic leaf seal as well as routing the lower sash rail and installing a piece of WS10 plastic tube seal where the sash meets the sill. Grooves can also be routed on the outer edges of the sash stiles and WS84 plastic seal installed there as well. All of these materials and methods are recommended as NPS “best practices,” and when installed properly are unobtrusive. Other companies make similar products.
Although storm windows can result in condensation and potential rot if used incorrectly, when installed properly and with an eye toward taste, they can be an attractive addition to the building. A fine example of this approach was employed by window specialists from Allegheny Restoration and can be seen at the Monroe County, West Virginia courthouse. If storm windows are not desirable, something as simple as insulated window treatments with no more than a quarter inch gap at the sides of the window opening can reduce heat loss by as much as 27%.
If the wooden windows are retained, they should be removed, prepared, primed, painted, and then re-glazed. Old caulking should be removed from around the exterior window frames and sills and then re-caulked. This will stop a great deal of cold air infiltration. After the sashes are re-roped and re-installed, two sash locks set a distance apart can then be used to keep the windows tightly shut.
The following paragraph was taken from the conclusion of National Park Service Preservation Brief #9 and reflects the opinion of Technical Preservation Services who recommend the retention and repair of original windows whenever possible. “We believe that the repair and weatherization of existing wooden windows is more practical than most people realize, and that many windows are unfortunately replaced because of a lack of awareness of techniques for evaluation, repair, and weatherization. Wooden windows which are repaired and properly maintained will have greatly extended service lives while contributing to the historic character of the building. Thus, an important element of a building's significance will have been preserved for the future.” As a preservation historian and past contractor I agree.
Written by Anna Lynn Stasick
As mentioned earlier, there are a number of options available for increasing energy efficiency, and when applied simultaneously, these methods can increase the overall efficiency of historic wooden windows dramatically. For example, much of the heat loss and air leakage involving historic wooden windows results from the hollow, un-insulated space created for the window weights on either side of the window sashes. However, replacing the window weights with spring-loaded window tape balances will eliminate the need for the weights thus allowing for the installation of insulating material in the now vacant sash boxes.
It is also possible to rout grooves in the meeting rails of the sashes and install RST Corporation’s WS87 offset plastic leaf seal as well as routing the lower sash rail and installing a piece of WS10 plastic tube seal where the sash meets the sill. Grooves can also be routed on the outer edges of the sash stiles and WS84 plastic seal installed there as well. All of these materials and methods are recommended as NPS “best practices,” and when installed properly are unobtrusive. Other companies make similar products.
Although storm windows can result in condensation and potential rot if used incorrectly, when installed properly and with an eye toward taste, they can be an attractive addition to the building. A fine example of this approach was employed by window specialists from Allegheny Restoration and can be seen at the Monroe County, West Virginia courthouse. If storm windows are not desirable, something as simple as insulated window treatments with no more than a quarter inch gap at the sides of the window opening can reduce heat loss by as much as 27%.
If the wooden windows are retained, they should be removed, prepared, primed, painted, and then re-glazed. Old caulking should be removed from around the exterior window frames and sills and then re-caulked. This will stop a great deal of cold air infiltration. After the sashes are re-roped and re-installed, two sash locks set a distance apart can then be used to keep the windows tightly shut.
The following paragraph was taken from the conclusion of National Park Service Preservation Brief #9 and reflects the opinion of Technical Preservation Services who recommend the retention and repair of original windows whenever possible. “We believe that the repair and weatherization of existing wooden windows is more practical than most people realize, and that many windows are unfortunately replaced because of a lack of awareness of techniques for evaluation, repair, and weatherization. Wooden windows which are repaired and properly maintained will have greatly extended service lives while contributing to the historic character of the building. Thus, an important element of a building's significance will have been preserved for the future.” As a preservation historian and past contractor I agree.
Written by Anna Lynn Stasick
The information in this article was taken from:
- Window Know-How: A Guide to Going Green, originally published in Preservation magazine March/April 2009
- National Park Service best practices Preservation Brief #9 entitled The Repair of Historic Wooden Windows,
- New Life for Old Double-Hung Windows, published in the November 6, 2007 edition of Fine Homebuilding magazine,
- Information provided during the March 30, 2009 meeting of the Collingswood, New Jersey Preservation Commission.
