Last night at the second of two US presidential debates, Donald Trump brought up something that baffled even those who often seem to have an excuse for the president’s colorful (and often quite inaccurate) commentary. Not the border wall, not refugees. Windows! No, not the operating system– the things in your house. Joe Biden wants to take away your windows! He wants to take away your windows and replace them with tiny windows!
It’s unclear where this comes from. At face value, it’s just another entry in a long canon of increasingly outlandish claims by the right wing– that the left wants to eliminate fossil fuels overnight, for example, ban hamburgers, or force teenaged girls to get taxpayer-funded late-term abortions from vending machines on every street corner. You know, the usual madness.
…those windows, tho
It is that time of year, though, when we’re thinking about our utility bills creeping up. So what’s the story with windows?
There is a joke in the Passive House scene that the most energy efficient building is just a box with no windows in it. It’s also not really a joke, because it’s true. (Germans invented the Passive House standard. Their building engineering is so good that we can’t hold their sense of humor against them). This is because, in building energy terms, windows are essentially gaping holes in the building envelope. (The envelope is the theoretical and physical assembly of boundaries holding conditioned air inside the building– and keeping water and UV rays out). Of course, no one wants to build buildings without windows. Those low-ceiling’d, small window’d, vinyl-sided houses in the burbs are already bad enough.
So, just how bad are windows? Should we care?
Well, yeah, they’re pretty bad. Compare this: a poorly built house in a jurisdiction that doesn’t follow the state-mandated building code (like Detroit) will have walls with an R-value of around R-10. R-13 batts might be used. But they’re probably going to be installed poorly. And, averaged over the rest of the wall assembly, that R-13 might come down to R-10. New code prescribes more like R-20 for walls. Windows, on the other hand? They’re like an R-3. Sure, you can get triple-glazed or quadruple-glazed windows– units that have four insulating layers. They’ll cost you a pretty penny.
And, experts generally agree, they’re not worth it.
“Unless there’s a mechanical reason why you want to replace the windows– for the sake of operation, let’s say, or to get rid of drafts- the return on investment from energy alone just isn’t there,” says Kevin McNeely, veteran energy consultant and Handbuilt co-conspirator. “It’s usually like a two hundred year payback.”
R-value of a properly designed roof is far higher than walls. Think R-49 or R-60. In the immortal words of Bill Rozendaal, slumlord extraordinaire of Grinnell, Iowa: “Well, heat does tend to rise.” So it does, sweet William. Adding just 10 square feet of skylight to a 200 square foot room with an R-49 ceiling will lower the mean R-value by about 5%. And so on and so forth.
But there’s hope!
This doesn’t mean you should replace all of your windows, by any means. Don’t despair. Unless your windows are severely deteriorated, replacement isn’t worth it. Window restoration fanatics, the Detroit Lions fans of the historic preservation world– desperate to convince you of the value of something they only believe in an aspirational sense- will argue that it’s not only vital, but also cheaper to restore old windows. This usually doesn’t prove to be the case. (10 severely deteriorated windows in our 1895 house we were looking to get replaced. We got a price for about $16,000– nearly double the replacement cost. It was going to take about three times longer than the timeline for ordering custom-manufactured new ones. But I digress).
In the mean time, don’t believe the conspiracy theory. Architects love glazing every damn thing, and they won’t stop. A massive building that’s 85% glass? Why not shoot for 90%? Green New Deal or not, architects are never going to give up their love for frankly excessive glazing. Of course, this just means we’ll have to get better technology to build windows. Vacuum insulated glass, for example, is not a new concept. But it’s only recently seeing more commercial adoption, as manufacturing techniques become more sophisticated.
Beyond new technology for manufacturing windows: increasing reliance on windows as vehicles for solar heat gain, heating thermal mass, and providing sunlight and fresh air are concepts older than architecture itself. But they’ve only received relatively recent attention in the high-performance building space, where flashy, hi-tech solutions often eclipse, well, common sense.
We’re getting there, though. Sorry, though, Mr. Trump– there will still be windows in the future. Remember to vote in a couple of weeks– for the future of our country and for fenestration.