The deluded world of window replacement

A British study suggests that conservation districts are preventing window replacements that would reduce carbon emissions. Good for them.

My 100 year old windows aren’t draughty. They are caulked and have inserts.

John Burn-Murdoch writes “It’s not easy being green when you live in a conservation area” for the Financial Times, (sorry, they have a high paywall) noting that in the UK there are a lot of historic and protected districts with planning restrictions that make energy efficiency upgrades difficult or costly.

“For most property owners, replacing draughty single-glazed windows with double glazing is simple. Consult a specialist, pick your new windows, have them installed. But if you live in one of the roughly 2.5mn properties inside UK conservation areas, you must apply for planning permission if your windows are not “like for like in material and appearance” — tricky in buildings that are often well over 100 years old — and sometimes even if they are. It’s a similar story with other retrofits such as external wall insulation.”

Yup, you have to ask for permission before you can take your historic building and wrap it in styrofoam and stucco and stick in vinyl windows. Burn-Murdoch calls these rules “arcane” and quotes a study, Regulatory barriers to climate action: evidence from conservation areas in England by Professor Thiemo Fetzer of The University of Warwick.

Fetzer “identifies a specific barrier to individual action in a specific domain. It documents and quantifies how this specific barrier is causing higher levels of energy consumption mostly from a hydrocarbon source: natural gas for space heating. It showcases and quantifies how this barrier is impeding individual action to lower carbon emissions.” The barrier is the requirement for planning approval in conservation areas to change windows, do exterior insulation, or add photovoltaics to the roof. Fetzer claims that these regulations “may be responsible for up to 3.2 million tons of avoidable CO2 emissions annually.” Fetzer notes that the energy upgrades would save between 5% and 15% of gas consumed, and calls it a “retrofit gap” caused by conservation rules.

Since I now can write what I want, I will get to the point: This is all bullshit.

I do not deny Fetzer’s conclusion; unimproved houses emit more carbon than improved ones. But when you read the 310 comments to the FT article, it’s all about windows, windows, windows. When you read the study, it’s all windows, windows, windows.

But when you look at where the main sources of heat losses are, it’s not windows. Study after study shows windows to be about 10% of the heat loss. Radiant heat loss through walls is another 10%. The biggest source of heat loss is through air leakage, as much as 40%.

Numbers vary depending on the study, but there are decades of evidence that window replacement has the worst bang for the buck of any action to reduce heat loss.

And who in their right mind would toss something made of natural old-growth wood that has lasted a hundred years for plastic and sealed glazing units that won’t last for a fraction of that time? As historic buildings consultant Donovan Rypkema has noted: “That is why they are called 'replacement' windows; you have to replace them every 30 years.”

It would be one thing if replacing the windows actually improved performance significantly, but blower door tests on properly restored 200-year-old windows demonstrated that they are as airtight as new windows. And if they are still draughty, add window inserts or exterior storm windows, and you have pretty good thermal performance without all the upfront carbon emissions of making new windows. And if windows are only 10% of heat loss, you have saved a lot of money that would have provided a very small saving.

Wrapping the house in styrofoam is even sillier. As Canadian expert Harold Orr has noted, “when you put styrofoam on the outside of a house you’re not making the house any tighter, all you’re doing is reducing the heat loss through the walls. If you take a look at a pie chart in terms of where the heat goes in a house, you’ll find that roughly 10% of your heat loss goes through the outside walls.” Orr may live in Canada but says, “I’m enough of a Scotsman that it bothers me to see people wasting their money. I go by houses every day, and I see them putting on an inch and a half of styrofoam, and lord help me – why don’t you do something for the same price and do it better?”

Meanwhile, going back to Fetzer’s study, which claims that these conservation measures are causing “higher levels of energy consumption mostly from a hydrocarbon source: natural gas for space heating.” How about taking the considerable cost of those new windows and exterior insulation and putting it into an air-source heat pump?

Harold Orr says we should “go after the big chunks.” That’s air sealing and attic insulation, floor insulation if you can do it. Engineer Toby Cambray calls for a combination of insulation and heatpumpification.

Those conservation area restrictions have done us all a great service; they have given us the time to learn that carbon and energy are two different things. So instead of having blocks of wonderful old houses covered in vinyl windows and acrylic stucco with combo gas boilers, all of which come with significant upfront and operating carbon emissions, we can now concentrate on insulating lofts, air sealing, and eliminating operating carbon with heat pumps.

Fetzer’s study and Burn-Murdoch’s article are more of an attack on historic preservation and conservation than a sensible discussion of building science and carbon emissions. They both ignore upfront carbon, air sealing, heat pumps, and everything we have learned in the last decade. They ignore the Passivhaus community that has shown how you can do Enerphit renovations that do not destroy heritage aspects of buildings, but also that if you can’t go that far, you can still eliminate your carbon emissions without wrapping your house in vinyl.

After the Economist wrote a misguided article on the same subject, I reworked the pyramid of energy conservation for the modern world for Treehugger. Insulating walls and replacing windows are right at the top in complexity and cost; that is where you end, not where you start. So don’t blame conservation districts; the world has changed.