Sweco Belgium
It’s one of the most pressing questions in the construction world today: what does “net-zero” actually mean, and how do we get there? Lode Lefevre, Project Engineer in Sustainable Design at Sweco, guides design and engineering teams towards more sustainable choices. As a strategic advisor on sustainability, he takes a critical look at trends, terminology, and how they’re being applied in practice.
“For me, everything starts with clear definitions,” says Lode. “Using the right scope and terminology is essential – yet surprisingly difficult.” The term ‘net-zero’ is notoriously vague in practice. “Are we talking about operational emissions only, or also embodied carbon? And what do we mean by ‘zero’?”
Operational vs. embodied CO₂: what’s included?
“The concept originally comes from the energy world: consuming the same amount of energy as you produce – not necessarily at the same time. That’s what ‘zero’ refers to.” This same logic is now being applied to embodied carbon via offsetting schemes. “But offsetting is far from straightforward. You’re dealing with CO₂-equivalents – meaning all greenhouse gases, not just CO₂. And planting a tree, for instance, only ‘pays off’ over several decades. Who can guarantee that tree will still be standing in 50 years?”
Energy buffering: key to true net-zero
Lode works on projects that tackle these issues in different ways – from energy-neutral buildings to designs that actively capture CO₂. But even in these flagship projects, major structural challenges remain. “Grid congestion is currently one of the biggest bottlenecks. We still rely on the grid to import and export energy, but the system is under strain. If we want to reach real zero, we need to move towards energy-autonomous buildings, with buffering as a key component.”
This fits within the still-relevant framework of the Trias Energetica: Limit energy demand, Generate renewable energy and Use energy efficiently. “That third step gets too little attention today. Without proper buffering, we’ll stay dependent on a grid that’s already stretched to its limits.”
The hidden impact of building materials
Another area of focus is material production. “Take concrete. It often gets a bad name, but the real culprit is cement and steel production – responsible for 6% of global CO₂ emissions. If we drive the energy transition in industry, we’ll reduce the embodied carbon in materials like concrete.”
Sweco applies the Trias Circularia framework for material choices: Use as little material as possible, Prioritise reused, recycled or low-impact materials and Ensure efficient use over the full lifecycle. “That also means designing for disassembly – and doing so without relying on closed ecosystems or predefined ‘kits of parts’. Those might work for small-scale systems or homes, but for large buildings, scale is a challenge. I see more potential in design principles that focus on adaptability and easy disassembly.”
Monitoring with the right data – harder than it looks
Monitoring plays a vital role in making buildings more sustainable – but only if you’re tracking the right metrics. “Operational emissions are spread over the lifespan of a building, but embodied emissions happen up front. That means you need to amortise them over as long a period as possible. If a building is demolished after just 15 years, most of the environmental benefits from low-carbon materials are lost.”
Sweco also offers commissioning, ensuring that buildings perform as designed. “But even then, data can be misleading. For data-driven optimisation to work, the data needs to be accurate, representative, and sufficient. And we need transparency in how it’s processed – otherwise you end up with a black box, or worse, a self-fulfilling prophecy.”
If you truly set the bar at zero, you have to acknowledge that building always has an impact. And it’s exactly that awareness that marks the beginning of real sustainability.
Lode Lefevre, project engineer sustainable design bij Sweco
Circular design is common sense – not a niche
For Lode, smart design starts with future-proof thinking. “Ask yourself: could I fix this myself? That’s often the best mindset. The materials we use today must remain relevant and replaceable 30 or 50 years from now. At Sweco, circular strategies like design for disassembly or extending the functional lifespan aren’t novelties – they’re basic logic.”
And who’s footing the bill?
The million-pound question remains: who pays for all this? “Without viable business models, these solutions won’t scale. Solar panels work because there’s a clear return on investment. But for technologies like aquathermy or sewer heat recovery, it’s more complex – public subsidies can help bridge the gap.”
That’s why Lode advocates for targeted subsidies and clear CO₂ targets. “Not everything will pay for itself. The government should step in where the societal return outweighs the financial one.”
The uncomfortable truth about ‘zero impact’
Ultimately, it’s not just about money – it’s about hard choices. “We’re still building as if zero-impact construction were possible. But how can we claim to build without impact while still building at this scale? What positive contributions are we making to offset all the negatives? Honestly, I think that’s an illusion.”
For Sweco, acknowledging that paradox is essential. “As long as we keep the definitions vague, we’ll keep circling the issue. If we truly aim for zero, we must first accept that every building has an impact. And that realisation is the starting point of true sustainability.”
Making sense of carbon metrics
There are several ways to measure the environmental impact of a building: CO₂, CO₂eq, CO₂eq/m², CO₂eq/m²/year, and CO₂eq/m²/year/intensity. But what do these indicators really mean, and how should they be used properly?
CO₂eq (carbon dioxide equivalent), or why planting trees isn’t enough
CO₂eq stands for carbon dioxide equivalent, a unit that allows us to compare the global warming potential of all greenhouse gases. Not all of them have the same effect on climate change. By converting them into CO₂ equivalents, we can express their total impact in a single, comparable metric. This includes gases like methane (CH₄), nitrous oxide (N₂O), and others – not just CO₂.
CO₂eq/m², or why we shouldn’t lose sight of the bigger picture
This refers to the total amount of CO₂ equivalents per square meter. It’s a metric that helps compare the environmental footprint of different buildings or design alternatives. A design may be highly efficient in terms of material use, yet still result in a greater overall impact than others.
It’s similar to the concept of building compactness: a large, compact building may perform better in kWh/m² than a small, poorly compact one. But in absolute terms, the smaller building still uses less energy overall.
CO₂eq/m²/year
This metric indicates the CO₂ equivalent emissions per square meter per year. It takes a building’s full lifespan into account and helps assess long-term sustainability. Embodied carbon – the emissions from construction and materials – is emitted all at once at the start. The longer the building lasts, the more that impact can be spread out. For instance, demolishing a building after just 15 years can cancel out many of the sustainable efforts made during construction.
CO₂eq/m²/year/intensity
This indicator goes one step further by factoring in how intensively a building is used. A 1000 m² building used by a single person for 60 years doesn’t offer much “added value,” even if it performs well on all previous criteria.
Think of car sharing: privately owned cars sit idle 95% of the time, while shared vehicles are used more intensively, reducing the total number needed – and thus their environmental impact. The same principle applies to buildings.
Real sustainability isn’t about offsetting – it’s about meaningful use
It’s not just about total emissions, but how efficiently and usefully a building performs over its lifetime. Designing for maximum value – that’s the difference between compensating and truly building sustainably.
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