- Author's Note: In the interest of full disclosure, I (Mike Bruno) sit on the Historic Preservation Commission for Geneva, IL. The opinions here are my own and do not necessarily reflect the opinions of the commission or the city of Geneva.
In the context of historic preservation, few topics can be as contentious as “new window” vs. “old window.”
There is a fairly broad public perception that the bodies regulating historic preservation in Geneva are unreasonable in demanding that property owners keep their “old drafty” windows in lieu of “new energy efficient” windows. This has become especially acute in this time of green initiatives and high energy prices. I hope to demonstrate here that—despite what window manufacturers would tell you—there is often no practical advantage to replacing your vintage windows.
This post will focus solely on the economics. A later post will focus on historic and aesthetic value of older windows along with the merits and shortcomings of old and new materials.
Physics informs us that there are two ways to lose energy through a window (or any other exterior house component.) The first is conduction where your precious interior warmth soaks into the walls and windows of your home and is radiated out to the environment. We typically mitigate this with materials that slow down that conduction such as fiberglass insulation in empty wall cavities to increase its “r-value”. (Interesting fact: it is not the fiberglass that is the insulating component, but the air trapped by the fiberglass that does the insulating work.)
The second vector of energy loss is through air infiltration, where gaps between exterior components allow air to flow freely between the interior and exterior of the building. In the case of older, unmaintained windows, it is the latter that represents the majority of heat loss.
Up front, I will acknowledge that if you have a 100-year-old window that has never been maintained and does not have a storm window, you probably are losing energy unnecessarily. The popular mis-conception is that the only way to address this energy loss is through putting your old windows in a landfill (the opposite of green) and writing a very large check to your window retailer. Such misinformation seems willfully propagated by those that profit from new window sales and installation. This is often accompanied by (necessarily) vague assurances that you will save enough money in heat and cooling to send all your kids to college. Let’s take a look at how window replacement can be a costly and ineffective effort for the homeowner (but a terrific solution for windows retailers.)
Probably the biggest red herring of the deba—and easiest to debunk—is the promotional claims pitting single-pane against multi-pane glass. To be sure, multi-pane glass does have a higher insulating value. But we must consider that a double glass pane has an r-value of just 2 compared with a single pane’s r-value of 1.
Unless you have windows floor-to-ceiling and corner-to-corner, simply replacing an r-1 material with an r-2 material will not appreciably affect the insulating value of the entire wall that might only be 15 percent windows. If we consider that the largest single vector for heat loss is the roof, we might typically calculate a percentage of overall energy savings in the low single digits on the virtues of multi-pane glass alone. You’re not going to extract any college tuition from those sorts of savings. This doesn’t even consider the option of simply adding a well-fitted storm window creating its own double-pane effect. But more on storm windows later.
As I said before, the vast majority of heat loss through older, un-maintained windows (and improperly installed new windows) is through air infiltration. If a homeowner is even remotely handy, that air infiltration can be cut by 80 percent or more for under $5 simply by application of some simple weather stripping between sash and frame and requires no power tools.
It should be understood that older windows were designed to be user serviceable. Contemporary windows are typically monolithic in design with little or no option for user maintenance. There is no question that the old wood-on-wood sash-to-frame contacts leave ample space for air (and energy) to pass. There are solutions to improving these seals that can get quite sophisticated that achieve parity with the finest new windows. If you are not particularly handy, then there are local companies that specialize in window restoration that can get your windows operational and weather-tight for less than the cost of a high quality replacement window. (We will visit LOW quality windows and their hidden cost in a future post.)
So once you have your old windows weather tight, you can still get the benefits of double-pane glass through the addition of well fitted storm windows. These don’t have to be expensive. Perusing the Home Depot website, they range from $30 to $53 for the aluminum multi-track models. I know, I know—they don’t look nice! I am not promoting aluminum storm windows; I am only focused on economics here for this post.
Given what we know so far, a reasonably handy homeowner can invest less than $65 and a little time and get all of the energy-saving benefits of a high quality replacement window (which can start at $500.) A more aesthetically pleasing (though still affordable) wood storm window can be procured from companies like Adams Architectural Millwork Co.
This merits a little digression here on aluminum storm windows. Geneva’s Historic Preservation Commission (HPC) often receives incredulous reactions when petitioners hear that “ugly” aluminum storm windows are permitted in the Historic District. There is no question that one would be hard pressed to describe extruded metal storm windows as an “architectural feature," but this speaks to an important premise in HPC decision making. Of primary concern for the HPC is that the change be reversible. While you won’t show up in any preservation or architectural magazines with metal triple-tracks, the window can be returned to its original form by removing the metal storm window.
To wrap up, you might be in an old home (such as many in Geneva’s historic district) with windows that are already in the vicinity of 100 years old. Window manufacturers can only stare at their shoes when asked if you can expect a similar service life. Old windows can often be made every bit as efficient as a high quality new window for well under $100 and can provide another century of use. Studies have shown that, on average, contemporary windows are replaced every 16 years. If you are looking simply to save money on energy and live more comfortably, it is very difficult to make the math support new, high-quality windows that might well exceed $500 per unit.
Next time: Historic vs. contemporary materials, artisanal millwork, historical manufacturing processes, and architectural character.