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(Bloomberg) — The three buildings, dotted around Norway, couldn’t look more different: a soaring timber-and-concrete obelisk in Porsgrunn; a squat, two-story Montessori school on the edge of a forest in Drøbak; and a concrete and glass wedge-shaped office in Trondheim, just a few hundred miles from the edge of the Arctic Circle. But they share a distinctive feature. Each has a roof perfectly tilted to squeeze out every possible drop of solar energy. 

They are called Powerhouses, and the initiative behind them claims they are all “energy positive”: The upfront energy “cost” of each building, and that of later demolition and disposal, is expected to be made back over the building’s lifetime. Powerhouses sometimes draw from the grid, especially in winter, but in the long Nordic summer days they give back many times over, overspilling excess solar energy into surrounding homes and businesses. 

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Buildings — the creation, running and dismantling of them — make up some 40% of the world’s carbon emissions. In the coming decades, as operational emissions from heating, lighting and other functions fall, the emissions from construction will make up an ever-greater share of that. Meanwhile, there’s a global building boom underway. Floor area is expected to double by 2060, a rate equivalent to adding an entire New York City to the world, every month, for 40 years.

Over decades, the green building movement has been trying to shrink the environmental footprint of construction. Now advances in technology and green-building laws are pushing ambition higher than net zero. Developers and architects around the world are touting their projects as “positive,” giving back more than they take, whether in terms of energy or carbon. But definitions of this vary widely, and some experts caution it’s just not possible to cancel out a building’s climate impacts.

Five Powerhouses have been built so far, all in Norway. A Powerhouse elsewhere in the world might look very different — it might use wave energy, or even kinetic energy from roads, for power, says Marius Hauland Næss, director of acquisition and business development for the Nordics for Snøhetta, an architecture firm that’s one of the companies involved in the initiative, which is ongoing. “Our Powerhouses have become very visible because you often see this angled roof,” Hauland Næss says. “Until now, solar power has been the main focus, but with the next generation of buildings we could be looking into ways to harvest and use wind, wave or geothermic energy.”

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The Powerhouse standard is about energy, not carbon. Designers and engineers just don’t know enough about the carbon intensity of the materials they build with to say conclusively that their buildings are also carbon-negative, says Hauland Næss. But a more efficiently built and operated building definitely means a shorter payback time. The first Powerhouse, Kjørbo, a set of offices near Oslo, reuses concrete and steel from the original 1980s buildings on the site. Powerhouse Lade, the first Powerhouse homes, completed this past August, have been designed to draw heat from natural thermal wells via heat pumps. Skanska, the project’s developer, says the complex’s 97 “energy positive” apartments will produce more energy than they consume over a lifetime of 60 years.

Demand for the approach is rising as European environmental regulations on business activities tighten. Snøhetta regularly turns down clients who ask for a Powerhouse, Hauland Næss says (though they usually tell them they can have a nearly-as-ambitious building). On a site like that of Bloomberg’s office in central London, a Powerhouse would be difficult to construct; there’s just not enough space for the solar panels (or wind turbines).

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“If people are talking about having a surplus of meeting their energy requirements from onsite energy generation, that may be a good thing, but it doesn’t mean that they’re doing no harm,” says Simon Wyatt, a partner in sustainability at the engineering consultancy Cundall. In other projects, “things may be better in terms of overall carbon footprint, but aren’t energy positive. And it’s understanding where every building should site itself.”

A rural location might make it easier for a building to generate more energy, but that doesn’t necessarily shrink the carbon footprint. A city-center building might not be energy positive, but it could be built in the most low-carbon way possible.

Populus, a Denver hotel that opened this fall, was built out of lower-emissions concrete. There’s no car parking on site, all food waste is composted and the lobby’s wood furnishings come from reclaimed snow fences from Wyoming and beetle-damaged trees from Colorado. The project was designed by Chicago-based architecture firm Studio Gang.  Jon Buerge, an Aspen, Colorado native and president of the developer Urban Villages, wanted to lean into a “reverence for nature” in the hotel’s design, to remind guests that this was no ordinary building. Nevertheless, the project ran into high-carbon headwinds — including in the kitchens, where the culinary staff insisted on gas stoves.

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Once construction was done, emissions stood at about 6,675 metric tons of CO2, roughly the same as the annual carbon emissions of 870 US homes. To offset this, Urban Villages bought carbon credits from sources including Grassroots Carbon, which pays ranchers to store carbon in their soil. They also planted 70,000 trees to replace forests damaged by beetle kill in Colorado, via the nonprofit One Tree Planted and the US Forest Service.  The hotel will also pay for one tree to be planted for every night’s stay. 

Overall, Buerge says, Urban Villages estimates that sequestration plans will remove 60,000 to 70,000 tons of carbon, though this figure hasn’t been certified by anyone outside of the company. The developer is billing the hotel as “carbon positive,” which it defines as “a commitment to sequester more carbon in biomass and soil than the combined embodied and operational footprints of the building throughout its entire lifecycle.”

“Our goal was to leave the planet in a better place than we found it — not an equal place, a better place,” says Buerge. “‘Carbon positive’ feels like a term that kind of emotionally reinforces what we’re trying to do.”

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Offsets are controversial: Investigations of several offset projects have found that they likely didn’t remove as much carbon as they claimed, and besides, there’s no guarantee that carbon can be stored in trees and soil forever. The Colorado tree-planting project has already seen losses of 80% because of heat and drought (the Forest Service is looking at replanting, Buerge says).

“You cannot build and operate a building without some level of carbon footprint,” says Buerge. He adds that cities and urban density are themselves good for the planet. With its downtown site and no parking, Populus nudges guests to walk and use public transit, avoiding the higher emissions from driving. 

There’s no fixed definition for an energy-positive, carbon-negative or climate-positive building, says Tom Wigg, a senior advisor for advancing net zero at the UK Green Building Council, an industry group that is part of efforts to create a net-zero carbon building standard. Instead of focusing on an individual structure’s carbon-in, carbon-out equation, he prefers to look at new buildings in the context of the global carbon budget. 

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“It’s not about mitigating your emissions at an individual asset level. It’s about the performance of your building being compatible with the entire built environment sector’s decarbonization to net zero, in line with the 1.5C scenario,” says Wigg. Any claim to go further than that is tough to evidence, he says: “We’ve got so far to go before buildings can really be called carbon positive, climate positive [or] carbon negative.”

In particular, the carbon footprint of the supply chain for materials has “only recently been intensively scrutinized,” says Mel Allwood, sustainable buildings director at design and engineering firm Arup. The true impacts of cement and steel, which rely heavily on fossil fuels and have high carbon emissions, and the toll of transporting materials over thousands of miles are difficult to quantify and difficult to reduce. “The collective impact is more significant than would have been anticipated in previous decades,” Allwood says.

The Launceston Timber Tower, in Tasmania, Australia, is “the most sustainable and carbon positive office development in Tasmania,” according to the website of its architects, Terroir. But Scott Balmforth, a director at the company, doesn’t want to go any further than that. Terroir didn’t want to claim “this is the way — this is how we’ve got to be doing it, this is ‘zero carbon,’” he says.

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It is possible to create a building that has captured more carbon than it emits at the point of its construction, a study commissioned by the firm found, but only using “biogenic” measures. These take into account carbon absorbed by timber and straw in the building during its former life as trees and crops (a controversial calculus, because cutting a tree down now means it stops absorbing carbon at a crucial juncture of the climate crisis, as well as uncertainty about what happens to that stored carbon at the end of the building’s life). 

The project opened Balmforth’s eyes to some of the contradictions in carbon accounting for buildings. For example, because under the biogenic method, more timber means more carbon absorbed, it can make the building look more “green” if you add more timber than you technically need — an obviously absurd approach if you’re truly attempting to create a building that treads more lightly on the planet. Such sharp practices are “alive and well” in the construction industry, he says, the consequence of a lack of clearly defined parameters for how to measure impact. “The industry is not at the point where we can really define what it is ourselves.”

Along with the Forest & Climate Leaders’ Partnership launched at COP27, Built by Nature is working on a set of principles for responsible timber construction. Principle number one? Don’t build a new building if you don’t really need to.

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