Architecture firm Perkins&Will has gone too far with claims that a luxury timber home on a Canadian mountain removes more atmospheric carbon than it emits, argues Fred A Bernstein.

For much of last winter, Perkins&Will, an architecture firm with 25 offices from San Francisco to Singapore to Sao Paulo, used a photo of a wooden house in British Columbia as one of the "hero images" on its website.

The house, which sits alone on a mountaintop overlooking the Soo Valley 90 miles north of Vancouver, is certainly beautiful, but the firm had other reasons for splashing it across its homepage. The 321-square-metre dwelling, known as the SoLo House, is meant to be a model of sustainability.

Entirely off the grid, it is designed to operate with power from 103 solar panels on its south facade, a 96-kilowatt-hour battery pack to store electricity for nights and cloudy days (both of which are frequent in British Columbia), and a hydrogen fuel cell for winter.

With all that equipment, the house may well be able to function without utility hook-ups. But Perkins&Will has made a far more surprising and audacious claim: that the building's structure is "beyond carbon neutral," meaning that it will remove more carbon from the atmosphere than it emitted in the first place.

It seemed to be giving its clients permission to build willy-nilly at a time of climate crisis

In a slickly produced video on the firm's website, Perkins&Will architect Alysia Baldwin says the house "proves that buildings can counteract their negative consequences and act as a source of repair."

People listen to Perkins&Will, a firm that has positioned itself as a leader in green building. "For nearly a quarter of a century, we've been at the vanguard of the sustainability movement," its website declares. Journalists have tended to repeat its claims.

But this time it had gone too far. By constructing a showplace of a house on an otherwise pristine mountaintop, and claiming it had helped the environment by doing so, it seemed to be giving its clients permission to build willy-nilly at a time of climate crisis.

Looking at SoLo House, with its cathedral ceilings, its comfortable sectional sofas and its giant picture windows, then listening to Perkins&Will claim that its structure reduces atmospheric carbon, I'm reminded of the old punchline: "Who are you going to believe – me, or your lying eyes?"

Reducing a building's contribution to atmospheric carbon means making it small, keeping it simple, building it near existing infrastructure, avoiding the need for heavy equipment such as batteries and fuel cells and using the lowest-embodied-energy building materials.

Reducing a building's contribution to atmospheric carbon means making it small

Perkins&Will, normally an excellent firm, has done those things on other projects. But with SoLo House, it seems not to have even tried.

According to experts, 40 per cent of atmospheric greenhouse gases come from buildings. Some emissions are attributable to running appliances and systems – so-called operational energy. The rest comes from the power needed to produce the building in the first place, known as embodied energy.

Incredibly, Perkins&Will is claiming there is "no embodied energy" in the house's structure (by which it means the elements that keep the building standing). To its credit, the firm answered requests for information promptly, providing facts, figures and charts prepared by Baldwin and her colleague Cillian Collins, a senior architect.

Here's how Baldwin and Collins arrived at their no-embodied-energy claim: First they estimated the amount of structural wood, steel and concrete in SoLo House. And then they turned to Athena Impact Estimator for Buildings, an app that approximates the amount of energy needed to produce given amounts of each building material and the amount of carbon released into the atmosphere as a result of that energy use.

Athena told them that producing the steel and concrete, harvesting the wood and so on in SoLo House released 122 tonnes of CO2 (sometimes called CO2e, for CO2 and its equivalents) into the atmosphere.

That should have been the beginning – not the end – of the process of calculating the building's embodied energy. There are hundreds of other items that needed to be counted. Start with the roof. The walls. The windows (a massive item, given the need for triple glazing). The solar panels, the batteries, the hydrogen fuel cells. The furniture. The appliances. The plumbing. The heating and cooling systems. Lots and lots of insulation.

The list goes on. Each of those items has significant embodied energy. Transporting all of those materials to a remote mountaintop site adds more.

Perkins&Will failed to account for those sources of embodied energy. Baldwin was clear, in a letter to me, that the calculations were limited to the structure. But why would anyone stop there? According to Baldwin, it's because structure "represents the largest contribution to a typical building's embodied carbon impacts."

It may also be because Athena only applies to structure. (Athena is meant primarily for comparing how the choice of a structural material affects a building's embodied energy. An architect might enter plans for the same building, once with a concrete frame and once with a steel frame, and see how the embodied carbon figures differ.)

Of course, there are other ways to estimate the house's total embodied energy; one method is to use an online tool called Tally, which provides information on the embodied energy of numerous building components. Counting everything isn't easy, but other firms have done it.

Perkins&Will had a way of making it vanish, if not from the atmosphere then from the balance sheet

Even so, according to Athena, the house emitted 122 tonnes of carbon into the atmosphere. That sounds like a lot of carbon, but Perkins&Will had a way of making it vanish, if not from the atmosphere then from the balance sheet.

Much of SoLo House is made of wood. Wood, like all plants, is produced by photosynthesis from ingredients that include carbon dioxide. Thus trees are said to store (or sequester) carbon. They do, but probably not as much as people think, as I learned by studying the question at length.

Here's Perkins&Will's theory: If you cut down a tree and use the wood as a building material, that carbon sequestered in that tree becomes part of the building. Then, if you plant a new tree in place of the one you cut down, the new tree will sequester additional carbon as it grows. Thus the process (cutting down one tree, planting another) results, net-net, in carbon being removed from the atmosphere.

There are so many problems with that theory it's hard to know where to begin. To name a few:

1) You have to be sure a new tree will be planted in place of the one you cut down; will get to be as big as the one you cut down; and will live a long, healthy life. (If a tree burns, or decomposes, as billions of trees do every year, its embodied carbon is released right into the atmosphere.)

2) You can't waste any of the wood. That's a problem because converting a tree into lumber usually turns half the wood into sawdust or chips, which could end up being burnt or allowed to decompose. This problem alone suggests carbon sequestration figures should be cut in half.

3) The wood has to stay in or on the building for a very long time. If the building needs repairs, and lumber is removed, it may be recycled, but it may also be burnt or allowed to decompose. And who'll be watching in 20 or 50 years?

4) Let's be honest: You could have planted the new tree somewhere else, and not cut down the first tree to begin with. For that reason, no number of trees excuses a wasteful building.

5) Even if the new trees do sequester carbon, the process will take decades. Scientists who study global warming warn of tipping points and thresholds, some of which could be reached within the next ten years. If new buildings help push atmospheric carbon levels to a point of no return, the sequestration accomplished by newly planted trees will be too little, too late.

6) It's a logical impossibility. If you really believe SoLo House repairs the atmosphere, all you have to do is build enough SoLo Houses and climate change will go away. Now for our next trick ...

No number of trees excuses a wasteful building

No wonder the theory is highly controversial. A whole lot of things have to happen just right for it to become a reality. As Baldwin wrote in an email: "We acknowledge that not all timber sources perform equally in the realm of embodied carbon reduction."

"Much of the embodied carbon reduction achieved by timber is directly attributed to sustainable forestry management practices that ensure forestry operations are carried out in a way that allows forests to remain healthy and viable for future generations," she added. "These practices include conservation and protection, land use planning, regulation of timber harvesting, establishing practices to ensure forest regrow, and continuous monitoring and reporting to government."

She went on to admit that the tool used to determine the building's sequestered carbon, WoodWorks Carbon Calculator, a product of the Washington-based Wood Products Council, considers "much of this storage to be temporary and therefore [does] not give the building a carbon credit for the carbon dioxide that will eventually be released from this wood some time down the road, through decay or incineration."

But that didn't stop the firm from banking on the theory when it performed its embodied energy calculation. Using the Carbon Calculator, it determined that the amount of lumber in the building would result in the removal – through the planting of new trees – of 145 tonnes of carbon from the atmosphere. That's a bit more than the 122 tonnes the firm says the building's timber, concrete, and steel released into the atmosphere.

Converting a tree into lumber usually turns half the wood into sawdust or chips

So in this case, reducing E (embodied carbon) by S (sequestered carbon) produces a negative number – minus 22 tonnes, meaning that building the house decreased the amount of carbon in the atmosphere. (Indeed, the house's owner, Delta Land Development, refers to it as "climate positive.")

Perkins & Will firm produced a chart to make this clear:

As Baldwin puts it, SoLo House "is able to store more carbon in its structure than was released during the production, manufacturing, and construction of the project."

That's a highly suspect statement. Based on everything I've learned, E (embodied energy) may be much greater than Perkins&Will says it is, and S (sequestered carbon) much lower.

In a letter responding to points in this article prior to publication, Perkins&Will wrote the following (the client, Delta Land Development, did not respond to requests for comment):

"Through careful selection of low embodied carbon and locally sourced materials, the project prioritized a mass timber structure. The design team used industry-accepted LCA [life cycle assessment] tools to quantify the carbon sequestration potential of the structure, and the timber structure is modelled to sequester 145 tonnes of CO2e as biogenic carbon."

Reusing/recycling is always the greenest strategy

"Structural elements typically represent the largest embodied carbon profile of [a] project, and as such, the structure was prioritized from an embodied carbon perspective."

"As designers, we rely on reputable industry tools to estimate the impact of projects. We used the Athena Impact Estimator for Buildings to complete this assessment. Athena uses ongoing research by the Athena Institute and complies with ISO 14040 (environmental management, life cycle assessment, and principles and framework) and ISO 14044 (environmental management, life cycle assessment, and requirements and guidelines)."

"Per our previous correspondence, we shared the Athena Institute's definition of biogenic sequestered carbon, which considers the whole life cycle of the material, including extraction, manufacturing, forms of transportation, installation, repair and maintenance, and end of life (assuming reuse of the wood)."

However, if Perkins and Will had really wanted to reduce embodied carbon, it would have thought about some of these strategies:

1) Putting the house in an easily accessible location, thus cutting out hundreds or thousands of trips by delivery people and construction workers. (Perkins&Will points out "that the wood was sourced from within British Columbia, and the building panels were manufactured in Pemberton, BC, which is located 30 minutes from the site.")

2) Renovating an existing house. Reusing/recycling is always the greenest strategy. Renovation typically generates 50 to 75 per cent less atmospheric carbon than new construction.

3) Choosing a site where there are no trees to cut down. According to Perkins&Will, "A clearing was required for a driveway, solar access, and fire protection. It required harvesting 180m³ of second-growth hemlock timber. This wood was put into the BC forestry chain, becoming useful lumber." Taking credit for sequestration by trees that may have been planted elsewhere, while cutting down enough trees on site to fill a five-meter by six-meter by six-meter container, is a whole lot of embodied irony.

4) Making the house a lot smaller. When it comes to saving energy, less is definitely more.

5) Choosing versions of steel and concrete with the lowest embodied energy (a lot of research is being done on ways of making those materials less "carbon-intensive").

Perkins&Will appears not to have done these things — the actual work required to reduce carbon emissions. The danger is that people will believe its claims.

Carbon revolution

This article is part of Dezeen's carbon revolution series, which explores how this miracle material could be removed from the atmosphere and put to use on earth. Read all the content at: www.dezeen.com/carbon.

The sky photograph used in the carbon revolution graphic is by Taylor van Riper via Unsplash.