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We’re sitting outside the entrance of Amsterdam’s public library, but you wouldn’t know we’re actually on top of a parking garage.
At street level, it feels like any ordinary city square: tourists dragging suitcases toward Centraal Station, bikes skimming past, a baby crying somewhere behind us, delivery vans humming in and out. It’s noisy, bright, busy — the usual Amsterdam blur.
What’s unusual is the shade we’re sitting in.
Above us is the canopy of a multi-stem tree whose roots never touch the ground. Around us are four modular “jungle blocks” from The Urban Jungle Project — 3D-printed structures made from recycled plastic, filled with a custom lightweight substrate, carrying four– to six-metre-tall trees. A tiny jungle hiding in plain sight.
Before The Urban Jungle Project arrived, this rooftop square was barren and brutally hot — just flat paving on concrete, radiating heat back into the city. The kind of leftover space you cross quickly because there’s no reason to linger.
Now: bees drift between branches, the air feels cooler, and people instinctively pause in the shade. A lifeless roof has become a place with atmosphere, texture, invitation. A place with a pulse.
Greening the “impossible”
This is exactly where Daan Grasveld likes to work: the spaces that shouldn’t be greenable, by any standard definition, anyway!
Roofs that were never engineered for soil. Squares tangled with cables and pipes. Balconies, façades, leftover corners of the city where conventional planting isn’t an option. All the places that fall outside the imagination of typical urban greening.
The Urban Jungle Project was founded to prove those definitions wrong.
Daan and his team have spent the last decade obsessing over a single question: how do you let nature thrive in places that weren’t designed for it?
Their answer is what he calls the three S’s: stress tests, substrate, and sensors.
Stress tests: stability in the sky
If you’re going to lift a tree into the air — onto a roof or public square — you have to replace what roots normally do.
Stress tests ensure the canopy won’t tip, shear, or tear free in a storm. Engineers run wind modelling, pull tests, and structural calculations so the system can sit on a roof without drilling, anchoring, or compromising the surface below. Everything remains modular, plug-and-play, and reversible.
Substrate: soil that isn’t soil
Conventional rooftop soil is heavy. Too heavy.
So The Urban Jungle Project developed a “jungle mix” — a lightweight substrate that’s less than half the saturated weight of typical rooftop soil but still holds enough water, air, and nutrients to keep a tree healthy. The goal isn’t rapid growth; it’s slow, steady, stable growth with full ecological impact.
Think of it as an urban bonsai with full-size benefits.
Sensors: seeing what trees can’t say
Sensors fill in the system’s blind spots. They track soil moisture, temperature, and electrical conductivity — especially important for projects in Berlin, Brussels, and Austria, where the team can’t visit regularly.
Sensors allow the team to water just enough, but not too much, and to learn across sites. Over time, the data sharpens, patterns emerge, and the system gets smarter.
Green-as-a-Service
The Urban Jungle Project doesn’t install greenery and walk away.
They call it green-as-a-service — long-term care, monitoring, and performance guarantees. Clients aren’t buying a product; they’re buying a living system that continues to function.
Remote data guides maintenance, while local contractors handle hands-on tasks. It’s a model built for scale: a distributed network of micro-forests, each linked by a shared intelligence.
Soon, anyone will be able to participate. Future jungle blocks will include QR codes that invite passersby to upload photos. AI will analyse canopy colour, density, and signs of stress.
Urban nature becomes visible, trackable, and co-managed. Stewardship becomes a shared act.
Still, Daan insists: sensors are not the goal. They’re an intermediate step.
The long-term vision is passive systems — water buffers trees can draw from capillarily, substrates tuned to hold just the right moisture, and evaporation models that replace constant sensing. Over time, trees become more autonomous and resilient.
For Daan, success means using the least amount of technology for the most amount of impact (me too!).
When “nothing” becomes something
Of course, critics argue that trees belong in the ground. And Daan agrees. But in cities, the comparison isn’t between a tree in a jungle block and a tree in a forest.
It’s between a tree in a jungle block and no tree at all.
Here on this roof, the difference is tangible. Without these blocks, there’d be nothing — no shade, no bees, no place to sit. Just a heat trap.
With them, the temperature in the shade can drop by 13°C. Birds arrive. Office workers linger. Kids climb onto the benches. A “dead space” becomes a social one.
Inside the library, looking down on the canopy, Daan reflects on what keeps him going: pride, humility, a family business now spanning generations, and the strange, beautiful challenge of building nature where the city forgot to make space for it.
Every site is different. Every tree is individual. Nature has been refining its intelligence far longer than we have. Their work is about meeting that intelligence halfway.
This episode is about that meeting point.
It’s about the rooftops, garages, and forgotten corners of the city.
It’s about designing for constraint, not perfection.
And it’s about treating even the smallest patch of hardscape as a place worthy of shade, habitat, and care.
A jungle on a rooftop may look improbable. But when you sit beneath its canopy, feeling 13°C of relief on a hot Amsterdam day, improbability starts to look like possibility.
Happy trails,
Nadina
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