Hey Reader,

I just came back from a training on nature-inclusivity in construction.

Spend a full day at TU Eindhoven with great input from the project partners of the Interreg project “natuur-inbouw”. We also got a tour over the campus where we saw more than 150 building-integrated nestboxes.

The same week I saw the five shortlisted designs for a competition in Rotterdam that finally triggered me to write this edition.

“Sustainable construction” is a world of trade-offs.

You have probably seen the pictures of a skyscraper covered in trees.

Balconies bursting with plants. Green cascading down a facade like a forest decided to go vertical.

It looks incredible. And ends up in every second sustainability presentation.

Almost every time, nobody asks the obvious question.

Is that actually sustainable?

The case for green buildings

There are real reasons to put nature into buildings, and they are worth taking seriously.

The most obvious one is wellbeing. Reader, would you prefer looking at a prosperous green terrace or at a blank concrete wall? I know my answer.

The research backs this up: access to greenery reduces stress, improves concentration, and makes people feel better about the spaces they work and live in.

Then there is biodiversity. Plants attract insects. Insects attract birds. In dense urban environments where natural habitat has been squeezed out almost entirely, even a modest green roof or planted facade creates something. Not a substitute for a real ecosystem, but much better than nothing.

Green surfaces also reduce the urban heat island effect. Vegetation cools through shade and evaporation. Research on the Bosco Verticale in Milan found measurable temperature reductions inside apartments during summer. In cities getting hotter every year, that is a fair argument.

And then there is carbon storage. Trees absorb CO₂ as they grow. According to research, urban trees sequester around 1 kg of CO₂ per square meter of canopy per year. Bosco Verticale claims significant absorption of CO₂ thanks to its 900 trees.

Sounds great.

Is that really so?

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What green buildings don’t put in the presentation

Here is what happens structurally when you decide to put trees on a balcony or a rooftop.

A tree needs soil. Not a flower pot of soil. Real, deep soil. At least 80 cm to root properly.

When it rained and the soil is completely wet, it weighs around 1000 kg per cubic meter. Now put that on a balcony twenty floors up and ask your structural engineer what they think.

What happens next is a cascade. Every extra kilogram on a roof or balcony travels through the entire structure. I’m not an engineer, but even I understand that concept.

Everything has to be sized to carry additional load. Thicker slabs. Bigger beams. Heavier columns. Deeper foundations. More concrete. More reinforcement steel.

A standard residential balcony is designed to carry people and furniture. A balcony built to hold a tree in 80 cm of saturated soil needs to carry several times that.

At Bosco Verticale, the balconies ended up 28 cm thick, compared to the 10 to 12 cm you would find on a standard apartment building. The most exposed trees got individual steel cages bolted to the structure to stop them overturning in storms.

For rooftops, the numbers are even bigger. An intensive green roof with enough soil depth for real trees carries a dead load of around 1,000 kg per square meter when wet. On a 1,000 m² rooftop, that is 1,000 extra tonnes the building has to carry.

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The Shift project in Rotterdam

Last week, the shortlist for the Shift Landmark in Rotterdam was announced.

The brief: a €240 million building described as “a 100% sustainable landmark” meant to inspire action on climate and circularity.

I looked at the five designs on the shortlist. They all look spectacular!

Most show organic shapes. Cascading greenery. Complex geometry covered in plants.

But that also sounds like more structure, more load, more concrete.

And that’s the huge trade-off and challenge in competitions and if you want to get everyone excited for the sustainable aspects of your project.

On a render you cannot see whether it’s made from low-carbon concrete, reused steel and in line with the ambitious Paris Proof framework. The materials look just like their traditional siblings.

But a design full of greenery and bold shapes: that draws much more attention. And I think that this would also be the perception of a visitor starring at this new landmark.

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You can’t have it all

Do you want a green building full of beautiful, healthy, tall-growing plants? Or do you want the building with the lowest possible embodied carbon footprint? Having both at the same time doesn’t seem possible.

That does not mean green buildings are wrong. To be honest: It makes me happy when I see a building like this.

Wellbeing, biodiversity and urban cooling are real benefits. And I haven’t even talked about air quality improvement and stormwater management.

But they advantages need to be weighed against what they cost structurally and in embodied carbon.

Next time you see this in a design proposal: challenge them on the embodied carbon. And then find a way to unite the best of two worlds.

Tip of the week While I’m wrapping up this edition, my young one is sitting close to me, playing with his noisy toys. Trying to stay sane, I’m listening to my "Building Beyond Focus" playlist that I created on Spotify a while ago: warm, slow tunes, no vocals, real instruments. Somewhere between jazz and hip-hop. I also listen to it a lot with my noise cancelling headphones in the office to avoid distractions. Just added a new song by Alfa Mist called “Like Something”. Nice intersection of jazz and hip-hop. Maybe you'll enjoy it as well.

Enjoy the rest of this beautiful sunny Sunday.

Best, Simon

Disclaimer

On a personal note: this newsletter represents my own thinking, not that of my employer or the boards I sit on. I write it because I find the topic important not on anyone’s behalf.