Restoring vs. replacing historic windows - data?
Submitted by murph on 2 September 2007 - 9:17am. energy | environment
Perhaps the most frequent and bitter of debates I see between historic preservationists and the average resident of an older home is window replacement. From the preservationist's standpoint, original windows are among the most important of defining characteristics of historic residential architecture. The typical rejoinder from the homeowner, convinced that replacing old drafty windows is key to home energy savings, is, "Okay, but are you going to pay my heating bills?"
The preservationist, in turn, will assert variously that significant energy savings can be achieved by properly restoring and weatherstripping the existing windows; that the return on investment from replacement windows vs. repair and weatherstripping is too low for replacement to be financially worthwhile; and, showing some savvy when dealing with purely environmentalist criticisms, that the embedded energy that goes into a replacement window is far greater than the lifetime savings of the replacement, and that the R-value of even a high-end energy efficient window is still very low.
But none of these assertions are very convincing to me, because they're just that - assertions, without any sort of empirical backing presented. And if I'm left somewhat cold (so to speak) by these data-free assertions, just think of the homeowner upset with his heating bills. One would think preservationists would have a strong interest in providing historic building owners that restoring their existing windows is a better investment than replacing them - changing an adversarial encounter into a cooperative one.
So far, though, even JSTOR has failed me in my search for empirical data. The only thing I've found so far (through Google) is a 1997 article from Home Energy Magazine, Creating windows of energy-saving opportunity. This study of the windows in 30 Vermont buildings, some unrestored, some restored, some replaced, entitles its conclusions section, "Preservationists take heart".
Our study of old windows showed that the energy savings are similar for a variety of retrofit and replacement strategies. Rates of return on investment for energy improvements are quite low when starting with typical or tight windows with storms in place, but are significantly higher when renovating loose windows with no storm.
The difference in annual energy savings between renovating an old sash and replacing it with a new one was very small--retrofits saved only a few dollars.
For preservations, the good news is that with a proper choice of renovation strategy and good workmanship, historic sashes can be almost as energy-efficient as replacements.
This is still not as thorough an article as I would like - as low-hanging fruit, costs of various options are shown in a table, and annual savings are discussed, but those numbers are nowhere combined to provide a direct comparison of ROI - all it would have taken was another column in an existing table.
Is anyone (Dale and Joe, I'm looking at you) aware of other empirical articles on historic window restoration versus replacement that provide clear evidence that restoration is a financially better option?