Anne Lacaton and Jean-Philippe Vassal, who won the Pritzker Prize for architecture earlier this year, have never worked in the U.S. And it’s possible they never will, given the gap between their approach to sustainability, which is about using less, and the American approach, which tends to involve buying and installing lots of stuff.

The Paris-based architects are best known for taking humdrum public housing blocks and making them larger and more livable by removing their facades and adding balconies. The results aren’t exactly beautiful, but they solve a problem without requiring a vast outlay of cash or carbon. “There are too many demolitions of existing buildings which are not old, which still have a life in front of them, which are not out of use,” said Lacaton. “We think that is too big a waste of materials.” Vassal put it even more simply: “Never demolish.” Their buildings go easy on the environment by leaving well enough alone.

That’s a hard sell in the U.S., where bigger is better, and people seem to believe that the way to make a building green is to make sure it has all the latest green equipment—an environmental oxymoron. The one thing that won’t solve a problem caused by overbuilding is more overbuilding.

That’s what makes HouseZero, designed by the global architecture firm Snøhetta (with energy consulting by Skanska Technology), so confounding. The once-modest house at 20 Sumner Road in Cambridge has been a media darling since 2017, when Harvard announced plans to transform it into an experimental building that would devour its own carbon footprint (though the university said it would need 100 years to do so). The renovated HouseZero, just a few hundred feet from the Graduate School of Design’s Gund Hall, would be a model of energy efficiency. The 46 solar panels on its roof would provide all the electricity it needed—and then some.

More and more buildings are declaring themselves capable of producing as much energy as they use. But HouseZero was meant to go further—producing enough clean energy not only to meet its current needs but to offset the carbon emitted during its recent transformation. In fact, Ali Malkawi, the director of Harvard’s Center for Green Buildings and Cities (CGBC), the entity behind HouseZero, began touting the house’s miraculous performance, writing in the present tense— as if it had already proved itself—long before it was even operational. Since October 2019, the CGBG website has said: “While very little energy is needed to run the house . . . HouseZero goes further by offsetting the hidden emissions generated throughout the building’s life cycle: from the fabrication and transport of building materials and construction processes, to maintenance and decommissioning.” That’s like a student turning in a lab report on an experiment that hasn’t happened yet. At Harvard!

Now the renovated house is more than two years old, and Malkawi still hasn’t released any data on how much energy the house is using or how much energy its solar panels are producing—essential numbers for evaluating any of his claims. But some publications, eager for good news about climate change, treated HouseZero as a done deal, a deus ex machina of decarbonization. On December 3, 2018, Fast Company proclaimed: “Two years ago, HouseZero was an ordinary old New England home. Now the house, built in 1924, is a model of ultra-efficiency, with zero carbon emissions, nearly zero energy for heating and cooling, and zero electric lighting during the day. Over its lifetime, it will produce more energy than it uses, plus more energy than was used in the renovation itself.” Then, on February 25, 2019, New York Magazine said that HouseZero “achieves a standard that few architects and developers hold themselves to, offsetting the energy used to manufacture, transport, and install the materials for its construction.” Both articles were written before the house went on-line.

Malkawi has given various explanations for not releasing data on the house’s energy production or consumption, despite his promises to be transparent. In an October 2019 email he wrote: “Once our databases are up and running and the fire department has signed off on our battery system, we will be monitoring this number and will be able to report the outcome.” His most recent email to RECORD, this week, promised to “let you know as soon as we have this information available for publication and it is verified.”              

Does it matter that Malkawi claims that the house has succeeded in offsetting its embodied energy, without producing any evidence so far (much less 100 years’ worth)? Yes. Because people tend to trust Harvard professors. And this professor has been saying for years that he’s got the embodied energy problem licked. In fact, averting climate catastrophe may require us to make big changes in what we build and how we build it. But HouseZero provides cover for the status quo: emit all the carbon we want during construction, the takeaway seems to be, because we know how to wipe the slate clean. And someday we may even prove it!

Carbon Conundrum

Most experts agree that, of the billions of tons of CO₂ and its equivalents released into the atmosphere each year, about 40 percent is emitted by buildings.

Of that percent, about two-thirds is the result of energy being used to power dishwashers and air conditioners, computers and lights, and any other systems or appliances. That’s called operational energy, and it’s the stuff most people think of when they think about the energy used by a building.

Fewer people think about the energy needed to create the building in the first place.  Everything from digging foundations to making concrete, from forging steel beams to assembling photovoltaic panels, requires energy and therefore emits carbon. These emissions are sometimes called upfront carbon, or embodied carbon (which is confusing because the carbon isn’t in the building—it was released into the atmosphere during fabrication and construction).

Unlike operational energy, which is easily measured (just check your electric bill), embodied carbon can be difficult to get a handle on. But carbon is carbon, and reducing the environmental impact of a building means reducing both its operational and its embodied energy.

Which poses a dilemma: efforts to decrease operational energy often increase embodied carbon, and vice versa.

HouseZero illustrates the problem. During its renovation, according to Harvard Magazine, “many tons of concrete mass were added in the floors between stories… as heat sinks to stabilize daily temperatures from night to day, and seasonally across frigid winters and scorching summers.” By stabilizing temperatures, these “thermal masses” reduced the building’s heating and cooling loads. But making cement—a key ingredient of concrete—releases large amounts of CO₂ into the atmosphere. Indeed, some scientists believe that 10 percent of all greenhouse gas emissions worldwide result from the use of concrete.

Did HouseZero’s designers, focused on operational efficiency, pay too little attention to embodied energy? This promotional video shows a simple frame dwelling becoming a new building stuffed with what appears to be enough lumber and concrete to build several ordinary houses. Snøhetta founder Kjetil Trædal Thorsen, who helped design HouseZero, said the foundation and some of the beams and rafters of the old house were retained, and that some of the new concrete was replaced with slag, which requires less energy to produce than the usual cement. Still, as evidence of an attempt to reduce energy use, the video reads as parody.

But parody or not, it represents tons of carbon being released into the atmosphere. If Harvard had wanted to create a house with low embodied energy, and one that could be a model for owners of old houses, it could have undertaken a more modest renovation, replacing only what really needed to be replaced. Asked whether the design favored operational energy reductions over embodied energy reductions, Malkawi wrote: “There is no simple answer yet. This is a lab building and our focus has been to try to balance and study all angles.”

Scientists who study global warming talk about tipping points and thresholds, some of which could be reached within a decade if levels of atmospheric carbon continue to rise. That’s why, despite the tendency to focus on operational energy, tackling the somewhat more abstract embodied energy problem is do-or-die. Embodied carbon is carbon released up front and en masse. If we release enough carbon now to hasten true climate catastrophe, it won’t matter if our lights are LED or incandescent.

More importantly, the carbon savings achieved by lowering operational energy is highly speculative. Architects and developers often make claims about energy efficiency that turn out to be wildly optimistic. That’s true even in the buildings’ first few years, when they are closely monitored. Who’s going to be watching 50 or 100 years from now? So, when a developer has to decide between reducing embodied carbon—carbon that is in the atmosphere by the time the building opens, or reducing operational energy, the former is the obvious and urgent choice.

So how much embodied energy is “in” HouseZero: In 2019 Malkawi switched from saying the amount would take 60 years to offset to saying it would take 100. Then, on the eve of publication of this article, he released an estimate of the embodied carbon in HouseZero to RECORD: “4.9 kg CO₂/m²/year, based on a 100-year service life assumption.” In other words,  490 kilograms of CO₂ per meter squared. The Carbon Leadership Forum’s Embodied Carbon Benchmark Study found the average embodied carbon of new single-family houses to be 239 kilograms of CO₂ per meter squared. That means the embodied carbon of HouseZero is, controlling for size, more than twice the average found in what is considered the best benchmark study to date.

The Sum of The Parts

Even so, when he tallied up HouseZero’s embodied energy, Malkawi excluded several items, including the batteries that store electricity when the skies are dark or cloudy, and portions of the geothermal system used to heat and cool the building, which he allocated to a possible future addition. And in a 2019 interview, Snøhetta’s Thorsen said major appliances, including refrigerators, weren’t counted, an omission that unfortunately is standard when calculating the embodied energy of buildings but means that the result underestimates the true environmental damage. Worse, he seemed to acknowledge the artificiality of the experiment when he told interviewer Nick Axel in e-flux architecture that the embodied energy of the original house also hadn’t been counted.

Axel:  How can you write off the embodied energy of the existing [building]?

Thorsen: Well, you can, when it comes to the project ... but you cannot when it comes to questions of justice and the global distribution of CO₂.

There’s another way in which the experiment avoids real-world conditions: HouseZero functions not as a house but as an office for the center’s 15 or so employees. That means there is no one doing laundry; no one cooking; no one using hot water for showers; no one using lights (or anything) at night, when the building is empty. Workers show up with their laptops—which might already be fully charged—and leave eight hours later barely having touched a switch. The need for electricity is minimal. That makes its applicability to actual houses weak.

Yet HouseZero is billed as a prototype. The goal is for millions of homeowners to apply its lessons and together make a dent in global warming. Malkawi told Fast Company that replicating its green features “can be done in a relatively inexpensive fashion.” Yet the Cambridge house was almost completely rebuilt to accommodate things like motors that open and close its windows automatically. Jaunty metal hoods were installed around some of the windows, and a striking, all-glass “solar chimney” uses sunlight to create thermal updrift. Neither Malkawi nor Harvard will disclose the cost of the renovation, which likely ran into the millions.

But even if the house were affordable, and even if it did everything Malkawi says it will do—if every bit of embodied energy in the house was offset by 2121—who would it help? Emitting all that carbon during the construction process, then promising to offset it over the course of a century, sounds like a cruel joke.    

Evergrande, the Chinese real estate developer that paid for HouseZero, no doubt welcomes the “build now, offset later” message. The company reportedly has 800 housing projects underway in some 280 Chinese cities. It is also building the world’s largest soccer stadium, a lotus-flower-inspired, 100,000-seat extravaganza in Guangzhou. And in March, it announced plans to build 268 luxury villas on what has until now been farmland in Hong Kong’s New Territories.

The largest of the villas, known as House One, will be about the size of New York City’s Grand Central Terminal. It will contain a swimming pool and four private elevators and will, according to the company, evoke the Palace of Versailles. So far, Evergrande hasn’t described it as green.

Whether Evergrande’s donation to the Center for Green Buildings and Cities, believed to be about $35 million, had an impact on the decisions made by Malkawi and others is impossible to know. Harvard has refused to give out any information on the amount or terms of the gift. (Whether it was paid as a lump sum, or arrives in annual installments, could easily affect how the center structures its research. Right now the list of “sample research projects” on the center’s website includes two involving China and none involving any other foreign country.)  A Harvard spokesman, asked about the gift, pointed this reporter to the university’s policy on conflicts of interest. That opacity about how projects are funded seems unworthy of an institution of higher learning that expects its research to matter.

According to its website, HouseZero is designed to address the “proposed emission cuts of the Paris agreement.” That includes helping the U.S. meet its goals for 2030. In that crucial year, HouseZero will use almost no operational energy, which certainly sounds like progress.

But the only reason HouseZero will look so good in 2030 is that its renovation had already spewed tons of carbon into the atmosphere. And carbon stays in the atmosphere for centuries. Releasing lots of carbon now, and hoping to “make it back” over the next 100 years, is shortsighted at best. As Bill Gates points out in How to Avoid a Climate Crisis, focusing on what we can achieve by 2030 will, in many cases, be counterproductive, because it misses the big picture. In terms of operational energy needs, HouseZero will look great, but its total contribution to atmospheric carbon tells a very different story.