Carbon: where the embodied is buried

Like most visitors to the Empire State Building, I found the view from the top quite astonishing: a towering sea of concrete, brick, steel and glass — billions upon billions of tonnes of it — stretching for mile after dizzying mile into the smog-hazed horizons of New York City. But just as memorable was the awestruck comment of the man leaning on the rail next to me: “Dear Lord,” he said, ”just look at all this … all this stuff!”

All this stuff is what embodied carbon is about. When materials are manufactured, energy is almost always consumed, often in large amounts. The World Steel Association estimates that the manufacture of steel is responsible for 7-9% of global carbon dioxide (CO₂) emissions from fossil fuels; a 2018 report from the Chatham House think tank put the contribution from concrete — also energy-intensive in its manufacture — at around 8%. Over the lifespan of a typical office building, analysis by Sturgis Carbon Profiling finds that embodied carbon might represent 35% of the total carbon “bill”. For a warehouse, the proportion rises to 47%; for a residential block, to 51%.

So there has been a dawning realization in recent years that it is not enough to reduce what has become known as “operational carbon” — that is, the carbon emitted by burning fossil fuels to heat, light, cool and power a building. If we are ever to get anywhere near a zero-carbon future, then embodied carbon too has to fall dramatically.

A tricky concept

There are reasons why embodied carbon tends to be relegated in importance behind operational carbon — not least that it is a harder sell. If designers can reduce energy costs, then that is an easily understood win-win. The client saves on fuel bills and the planet suffers less. In contrast, a building owner or a developer might question why it’s in their interest to take on any cost associated with material choices that reduce embodied carbon.

But altruism is far from the only reason to opt for low embodied carbon design, according to Fiona McGarvey, senior sustainability consultant at WSP in London. Many building clients now have corporate-level targets on reaching net-zero carbon, she points out: “It’s not possible to do that without considering embodied carbon. For many companies the only realistic way to achieve it will be by purchasing offsets — so they may find it’s actually cheaper to pay more to reduce embodied carbon than to do business as normal and pay for the offsets.” Then there is the potential reputational damage of not addressing your carbon footprint: “Effectively another cost to set against the effort to design with carbon in mind.”

In any case, low embodied carbon design does not necessarily cost more: “Quite often the way to reduce it is simply to come up with a design that uses less material and wastes fewer material resources. Do that and you are quite probably saving money too.”

So embodied carbon is moving up the corporate and environmental agenda. It features prominently, for example, in the international Architects Declare and Engineers Declare manifestos that in 2019 called on designers to recognize their responsibilities and up their game with regard to carbon emissions and climate change.

Becoming more widely considered, however, does not make embodied carbon any less of a slippery, moving target of a concept. It is so notoriously hard to define and calculate that a whole terminology has developed around the effort to pin it down. When attempting to calculate the embodied carbon of steel, for example, do you include only the energy involved in production from the iron mine to the point at which it leaves the steel mill (“cradle to gate”), or also its transport and installation (“cradle to site”), or its end-of-life recycling or otherwise (“cradle to grave”).

Even within these definitions, there is controversy. Cradle to site will include carbon emitted by the delivery truck’s diesel engine — but could it conceivably also include the back-office activities of the logistics company or even a percentage of the carbon expended in manufacturing the truck? Where, exactly, should the buck stop?

Katie Symons, a former WSP sustainability consultant working as an adviser to the New Zealand government to incorporate climate change initiatives in building regulations, cautions against getting drawn too deeply into this debate: “There is a whole profession of people who get excited about ‘system boundaries’ and argue about this till the cows come home. Sure, everything to do with embodied carbon is a model and everything is inaccurate to a degree. But the value lies in comparative analysis — compare apples with apples and it’s okay if the figures are not perfect.”

Neither is it necessary to get bogged down in the minutiae. “There is more information available about large steel and concrete components than there is about window catches. But this is not really a problem. Employ the 80-20 rule of thumb; probably 80% of what you’re concerned with will be dealt with by 20% of what you can affect. So to reduce the embodied carbon of a building, focus on the big wins — the foundations, frame, roof, cladding and linings — not the taps or door knobs.”

Biographical materials

When it comes to specifying materials with lower embodied carbon, there is now considerably more information available to help designers than there used to be. A big change over the last five to ten years has been an increase in environmental product declarations (EPDs). Like carbon footprint certificates for products, these are paid for by the manufacturer but carried out and independently certified in accordance with international standards on life cycle assessment (LCA). “A few years ago there would only be the odd construction product, but now there are lots, allowing a lot of comparative analyses to be made,” says Symons. “They are playing a big part in bringing credibility to embodied carbon calculations, which are inevitably far more opaque than those for operational carbon.”

More help for designers has come in the form of fast-developing design software. Tally, for example, is a plugin that allows Revit users to imbue their building information models with information about the materials and architectural products their completed structures will contain. In addition to quantifying emissions to land, air, and water, Tally also factors a building or material’s embodied environmental impacts. Another, often used in conjunction with Tally, is GaBi — essentially a data platform offering LCA information, including embodied carbon values, for a huge range of components. Simpler, and sometimes free, whole-building LCA software is also available, such as Athena Impact Estimator, openLCA and One Click LCA.

“These aids mean that we can have a lot more confidence in the figures than more generalized ones we might have been offered ten years ago,” says Symons. But it is still important that the software is regularly updated and country-specific, she notes. “Aluminium made in New Zealand, for example, comes from plants powered by hydro, so has very low embodied carbon compared with aluminium produced by a fossil fuel powered grid elsewhere. Also, as grids decarbonize, values will change. Good software can help designers keep up with changes like that.”

Early-stage simulations

One issue that programmers are only just starting to address, however, is early-stage design. As Symons puts it: “You can get decent figures for the building you have designed — but what about the one you are just thinking about? How do you get a figure for that?”

According to Jeremy Gregory, a research scientist at Massachusetts Institute of Technology, this is a vital point — for while EPDs and Tally can help design a building made from lower embodied carbon products, it may be that a different kind of building could have performed even better. “The problem is, by the time you apply the software, too many of your decisions are locked in,” he says. “It doesn’t really support decisions in the earliest phases, particularly when you are trying to look at both operational and embodied carbon in a whole-life perspective.”

Together with colleagues at MIT, Gregory has come up with software that attempts to solve this problem: “We know that designers already do this with cost — so, if you like, we are trying to do the same with the cost of the carbon. Our software enables designers to simulate many different kinds of buildings when they are thinking about basics such as massing, height, even location, and shows them the parameters and ranges of uncertainty. So they might discover that for a certain building, up to a certain height, concrete might be best, but above so many storeys then maybe steel might be the way to go.”

As Gregory says, these decisions will often involve looking at the interactions between operational and embodied carbon. There is much scope for argument here, particularly around the claim that concrete buildings, while tending to have a high embodied carbon, reduce operational carbon by having a high thermal mass.

This assertion has become almost a cause celebre among designers who care about embodied carbon. Gregory himself is a director of the US Concrete Sustainability Hub, and so has an interest in pointing out concrete’s positives. Others see concrete as the very devil and declare that it should be purged from all design as much as possible.

The crucial question — or assumption — is how long a building is going to last and what will eventually become of it at the end of its useful life. This is at the heart of all and every consideration of the trade-off between operational and embodied carbon, says Chris Pembridge, director at WSP and chair of the sustainability panel of the UK’s Institution of Structural Engineers. “We need to agree what design life means and what end-of-use looks like,” he says. “If a building lasts twice as long as expected, then obviously its operational efficiency becomes more important. If it is somehow recycled or reused then that changes the way you think about its embodied carbon.”

Future unknowns can at times make decision-making almost impossible: “Even within our panel there are very opposite views. Should we reduce embodied carbon by designing buildings to last as long as possible and so reduce the need for new buildings in the future? Or should we design low embodied carbon, ‘throwaway’ short-term buildings because there’s no way of knowing if a building can keep its relevance? I honestly don’t know the answer.”

Going circular

But that doesn’t mean that there are no good decisions to be made: “There is a lot we can and should be thinking about that will help reduce embodied carbon in all kinds of buildings.” Developing adaptable building designs, Pembridge says, is vital if the materials and carbon bill of future generations is to be reduced. A recent project involved designing a shopping centre car park: “But we are envisaging improvements in public transport, so less need for cars in the future. We don’t want the concrete of the car park to become surplus to requirements, so we have designed it so the lower two storeys can be easily remodelled as retail space.”

Pembridge believes that totally reusable buildings can and should be designed more often: “We recently looked at dismantling a large steel-framed store in London and re-erecting it in south-west England. Its frame could have been reassembled anywhere. Sadly we couldn’t quite get the logistics to stack up.” Even components from concrete buildings could be looked at in this way. “Why not have a stamp on every precast beam saying what it is and what it can do?”

To reach a point where substantial amounts of construction materials can not only be recycled but also reused would seem to be a priority now. Neither the commercial nor the technical infrastructure currently exists — with the result that even those such as Pembridge who attempt it can seldom make it work.

A little regulatory tweaking might be needed to make reuse commercially viable — a tax break here, an extra LEED or BREEAM credit there. But there is hope that the technology, at least, already exists to facilitate it. Fiona McGarvey explains: “To achieve a circular economy of materials, you need to know exactly what is in a building. At the moment, there is a lack of materials transparency in the industry and it is not always clear what materials are in a component, or how to keep track of what is procured and installed. You might end up with high embodied carbon aluminium in your cladding when you specified low. However, blockchain offers a way of recording and tracking materials through the supply chain in real time, so you could know what was actually installed and what its true carbon value is. This would enable you, for example, to sell on the steel and other components of a building before it is demolished.”

In this way, she explains, the world’s building stock would eventually become a mineable resource, hugely reducing the need for new materials and thereby slashing the carbon cost of producing new stuff. Such a vision is obviously some way off, but there seems no reason why reuse could not at least begin to increase rapidly from its current, almost non-existent levels.

There is also a simpler way to reuse existing stock. “The greenest building is the one that is already built,” is an increasingly cited quote from US architect Carl Elefante — and when it comes to embodied carbon at least, he surely has a point. Both the steel and the concrete lobbies are onto this, and are keen to highlight the longevity of their structures. But longevity is not usually the problem, points out Julie Sinistore, project director for sustainability, energy and climate change at WSP, based in Oregon, who focuses on life cycle assessment. “Commercial buildings are not usually demolished because they become unsound. It is because they go out of fashion or land values change and a different sort of building becomes the preferred option.”

In terms of embodied carbon this is wasteful in the extreme, but Sinistore has an uplifting solution. “Build beautiful,” she suggests. “The more beautiful your building, the more people will love it and the less likely it is to be demolished.” As a way of reducing the future burden of embodied carbon, this is a peach. There are, after all, no plans to knock down the Empire State Building.