In the world of residential architecture, the phrase “net-zero” has become ubiquitous. This sprawling glass-and-steel house deserves the label, according to The New York Times; so does this luxury-filled craftsman-style dwelling, The Washington Post reports. The trouble is, it’s hard to imagine any house more complicated than an igloo actually making the cut. These two houses don’t even come close.
And it matters. Because when the Times dubs a 7,000-square-foot house with a reflecting pond “net-zero,” it suggests that we can fight global warming without making major changes in what we build and how we build it. And that’s a dangerous message to send.
The “net-zero” claims tend to originate with architects or developers. It’s understandable that they would want to depict their buildings as environmentally benign—their self-esteem and, increasingly, their bottom lines depend on it. The phrase has even been used to describe buildings still under construction. Architects, developers, and journalists, using the present tense, tout the environmental bona fides of buildings that haven’t even opened. The finished buildings rarely live up to the hype, but you’ll never see a press release admitting it, or a retraction in a publication that bore the falsely reassuring headline. Misstatements made by interested parties are unfortunate, but it’s worse when newspapers and magazines—which are supposed to stick to facts—transmit the claims uncritically.
Let’s start with a definition: A net-zero building is one that generates as much energy as it uses. Simple, right? One side of the equation is energy consumption. Every building, except maybe the igloo, needs energy for running lights, appliances, heating, and other systems. On the other side is production. Happily, some buildings do generate clean energy, usually via rooftop solar panels. Sadly, few buildings can produce as much energy as they use 24-7-52; solar panels aren’t efficient enough and batteries have limited capacity. Additional energy has to come from somewhere.
Often that “somewhere” is an off-site wind or solar farm, a “net-zero” deus ex machina. For years Apple has been describing its Cupertino headquarters—that vast, donut-shaped building—as “powered by 100 percent renewable energy.” But Apple is counting energy produced almost 200 miles from Cupertino, at its giant solar farm called California Flats, and stored in rows of Tesla batteries, as part of the energy output of its building. It’s good that Apple is investing in photovoltaics, but calling a building “net-zero [if you include off-site energy production]” tells you nothing about how green the building is. You could, after all, power the world’s most wasteful building with solar panels if you had a big enough array of them. That’s an accounting trick, not an environmental strategy.
Even worse, some buildings are called net-zero because their owners plan to purchase carbon offsets. (Notice the future tense. There’s a lot of early chicken-counting.) In most cases, the offsets involve planting trees hundreds or thousands of miles away. The theory is that because trees store, or sequester, carbon, planting them can balance out emissions. But relying on sequestration to negate a building’s carbon emissions makes it possible to “greenwash” any building, no matter how energy-inefficient.
What would it take to make these tree-planting initiatives legitimate? You’d have to know how much carbon a tree will actually sequester in its lifetime, keeping in mind that climate change itself is affecting the trees’ capacity to absorb carbon. You’d have to know if a tree is being planted on land that’s barren or an area where trees would naturally regenerate. You have to be sure it wouldn’t have been planted there anyway, and you have to be sure that it lives a long, healthy life. (If a tree burns, or decomposes, as billions of trees do every year, the carbon it stored gets released back into the atmosphere—exactly where you don’t want it to be.) In other words, you’d have to monitor the trees for as long as the building stands, which could be a century or more.
But no one is promising to watch trees for a hundred years. And that’s the problem: The carbon a building emits during construction is in the atmosphere, exacerbating global warming right this minute, while the corresponding sequestration will happen over decades, if at all. Calling a building “net-zero” because of carbon offsets that may never exist is replacing fact with fantasy. If you think that’s harsh, read The Guardian’s devastating takedown of rainforest-based carbon offsets, concluding that “90 percent [of them] are worthless.” In other words, carbon offsets aren’t working. But even if they were, they would tell you nothing about the energy efficiency of the building in question.
There’s another reason most buildings can never be net-zero. That reason, the elephant in the room, is that it takes a lot of energy to make a building. The energy needed to, say, extract raw materials from the ground, turn those materials into building parts, and ship those parts to the construction site and hoist them into place, is called “embodied energy.” Embodied energy is harder to measure than operational energy, though several excellent digital tools are making the job easier. In any case, ignoring embodied energy because it’s difficult to quantify is like saying it’s okay to eat an entire chocolate cake while on a diet because you don’t know its exact calorie count.
Yet almost no one counts embodied energy when pronouncing a building “net-zero.” I know, because I’ve asked architects, engineers, developers, and building owners, who limit the consumption side of the equation to operational energy. They either don’t know about embodied energy, or know about it but proceed as if they don’t.
This is more than a small oversight: A building’s embodied energy can be many times greater than its annual operational energy use. A couple of years ago, architects at Harvard’s Graduate School of Design retrofitted an old house in Cambridge to demonstrate the nth degree of energy efficiency. But they chose features that would reduce the building’s operational energy needs in part by increasing its embodied energy. For example, they opted to use slabs of concrete as “thermal masses.” (The slabs absorb heat by day and shed it by night, reducing the need for heating and air conditioning.)
But concrete requires cement, which is commonly made from limestone in a process that releases massive quantities of greenhouse gasses. In part because of the concrete, it could take a hundred years or more for the renovation’s operational energy savings to zero out its embodied energy cost. That means the much-publicized retrofit won’t begin to reduce the amount of carbon in the atmosphere until well into the 22nd century. Which seems a very poor strategy for addressing a current climate crisis, with tipping points mere years away.
What the Harvard architects did is what many building owners are doing now, in places like New York, that have set deadlines for cutting carbon emissions: They are, knowingly or not, front-loading their carbon “expenditures,” in order to avoid emitting lots of carbon once the limits take effect.
Imagine you’re a college student spending $4,000 a month on food and entertainment. Your parents tell you that you’ll have to cut your spending in half starting February 1. So you prepay your next 10 years’ worth of expenses, and then announce to your parents that you’ve cut your monthly outlay to the bone. That’s what property owners are doing, often inadvertently, with energy retrofits: emitting lots of carbon now to avoid emitting carbon later. (Which is why laws demanding cuts in operational energy without limiting embodied energy may be counterproductive.)
I’ve been doing my part to expose the misuses not just of “net-zero,” but also of “carbon neutral” (a close cousin), and variants like “climate positive” and “carbon positive.” “near-zero” and “climate neutral” are also trending.
The next time you encounter one of those terms, you might want to ask:
How much energy is needed to operate the building?
How much energy did it take to build the building?
How much clean energy does the building produce?
If the clean energy production isn’t enough to cover the building’s operational energy and offset its embodied energy in, say, a decade or less, the building isn’t helping the environment. And it isn’t net-zero in any way that matters.
Some 40 percent of the world’s carbon emissions come from buildings. To reduce buildings’ contribution to climate change will require us to build smaller and lighter and with natural materials. Applying the “net-zero” label to buildings that depend on off-site solar farms and illusory offsets, and without counting embodied energy, makes a mockery of real efforts to mitigate climate change.