When walking through Rotterdam, the city’s difference from its neighbouring towns and cities is immediately clear. Unlike many historic European centres, much of Rotterdam’s architecture dates back decades rather than centuries. After the devastation of World War II, the city rebuilt at speed, creating a modern urban landscape defined by bold design, post-war construction and, importantly, a vast number of flat roofs.
Today, at a time of growing housing pressure and limited space for new development, Rotterdam is looking upwards. Through its Topping Up project, led by Project Director Yvonne Rijpers, the city is exploring the potential of its “next layer”: 18.5 square kilometres of unused flat rooftops above the streets. More than an architectural idea, the project is a strategic response to urban density, sustainability and social need, showing how cities can create new space without expanding outwards.
Densifying without disturbance
You use the same roads, and use the same schools. In that sense, it's really sustainable.”
Urban growth traditionally means expanding outward into green spaces or tearing down old structures to build taller. However, Yvonne Rijpers explains that Topping up offers a much more “reactive” and sustainable alternative. Building on top of existing structures allows the city to leave its existing infrastructure intact while also utilising it to expand further.
“It’s a sustainable way of densifying your city,” Rijpers notes. “You use the same roads, and use the same schools. In that sense, it’s really sustainable.”
This vertical expansion is particularly vital now that the ‘strain’ of the housing crisis has reached a boiling point. Excepting that ground-level space is the most premium development, the provincial and national governments have stepped in with subsidies to turn these rooftop maps into real homes.
The “Aha moment” on the horizon
The vision for this project came years ago, from a friend of Yvonne’s, at a festival where local enthusiasts began organising rooftop days to show citizens the hidden potential of their skyline.
The festivals themselves were a huge success, although creating actual substance was slow. The turning point came from a dedicated research project, Rotterdam Rooftops, where they mapped the city’s potential and discovered a staggering figure: the city could technically accommodate 60,000 new houses on existing rooftops.
We have 18.5 square kilometres of flat roof in the city, which is like 3,000 football fields
“We have 18.5 square kilometres of flat roof in the city, which is like 3,000 football fields,” says Yvonne. “From all the Dutch cities, we have the most architecture… it was quickly built, lots of flat roofs. We have very big potential.”
Penthouses for the people
Rooftop living has historically been for the elite, but Rotterdam is flipping that script. The municipality recently made a decision that means any developer who creates ‘Topping Up’ units must designate them as social or middle-class housing. These developers will be exempt from certain municipal fees typically required when creating new land value.
“We are really realising these ‘penthouses for the people,’” Yvonne says proudly. “It’s going to be affordable housing on the rooftops. That is really important.”
Looking past strictly affordability, the project is truly embracing the idea of circularity. The city is offering incentives for developers who use bio-based or circular building systems, such as lightweight timber or modular units that wouldn’t stress the existing foundations and that would minimise the carbon footprint of construction.
A modern model
“If you want to make it happen, you really have to facilitate the process,” Yvonne says. Navigating parking policies, ground prices, and homeowner association rules can be a labyrinth. “It’s really about simplifying and facilitating.”
I hope we have hundreds or even thousands of new homes for Rotterdam and the new people
The municipality has transformed its role from being a traditional regulator to now being a facilitator. The municipality now helps homeowner associations earn money through rooftop sales, which can then be reinvested into making the original building more sustainable.
What will Rotterdam look like in a decade? “I hope we have hundreds or even thousands of new homes for Rotterdam and the new people,” Yvonne concludes. “And that we are proud that this city… respects the city’s grain and quality to the neighbourhoods and also toward the home underneath”.
A denser, greener, and more inclusive Rotterdam is on the horizon.
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Photos copyright City of Rotterdam
