Report International Rooftop Knowledge Day 2022

The International Rooftop Knowledge Day took place on June 3rd 2022. Once again, it returned to a live setting. 180 visitors traversed the Rooftop Walk, and thereafter joined smaller group sessions for lunch workshops, gathering in the afternoon on top of The New Institute, at The Podium for a full program on top of and about… rooftops. 

This report summarizes some of the most important insights shared during the discussions after the visit to the Rooftop Walk and during the afternoon program.  

The Rotterdam Rooftop Walk

These days, being on a rooftop isn’t only about taking in the views. It’s about learning something too. Rooftop Days celebrate the novel concept of occupying and utilizing this layer of the city and sharing it with the people, or rather, bringing the people to it.

As they climbed the first orange cascade of steps beside the World Trade Centre, crossing Coolsingel to de Bijenkorf, to a parkade rooftop with the ghost frames of a would-be rooftop village, Knowledge Day visitors wandered through a series of provocative interpretive installations demonstrating how innovative rooftop use can maximise this underdeveloped, and under celebrated – yet essential – part of the urban landscape. 

Knowledge Day Kickoff – Rotterdam Building

The Rooftop Walk culminated in an informal, pre-lunch discussion in the event space adjoining the inspiring rooftop balcony of the Rotterdam Building where Bas Mastboom – Rotterdamse Dakendagen Knowledge Programme and Production Coordinator – kicked things off with a brief introduction to the day’s events. Inviting newly minted Rotterdamse Dakendagen Director Nikki Kamps to the stage, the two pondered over the challenge and opportunities inherent to making the largely private territory of the rooftop landscape more public, or rather transferring the attractive qualities that private rooftop terraces afford the lucky few, to rooftops distributed throughout the city where the public can enjoy and partake in the rooftop experience. 

To understand how to begin and how to mobilise on a micro level, they invited Rotterdam resident, and rooftop owner, Wim Steassens, to share his insights on how he and his partner made their Rotterdam rooftop oasis “happen,” enhancing its accommodation with each year so that it now even boasts a rooftop bathtub, shower, lush planting, and a kitchen for entertaining!

“How do we transfer the private values of rooftops to the public sphere?” said Kamps, “and what we can learn from these private adventures in rooftop development, and thereafter apply to inspire public policy changes that facilitate changes in how we use rooftops in the city, as well as who has access to them?”

This was a provocative discussion to carry into the lunchtime workshops, and good fodder for the afternoon plenary sessions on Het Podium that were to explore both the practical and whimsical aspects of rooftops as activated, social, and productive spaces in the city fabric.

Afternoon Plenary Sessions – Het Podium

The afternoon program consisted of multiple conversations about rooftop use and development, from different perspectives. After the welcoming words, the first 3 conversations involved current practices and developments, and how to influence policies. After the presentation of the rooftop-hero-award, there was a panel-conversation about the possibilities of rooftop-use in the future.  

Each conversation is summarized in the text below.  

Welcoming words from Team Knowledge Day, with reflections from Barbara Luns (Architecture Instituut Rotterdam), and Léon van Geest (Rotterdamse Dakdagen)

On stage

Barbara Luns: Director, Architecture Instituut Rotterdam
Léon van Geest – Director, Rotterdamse Dakendagen
Sophie Stravens – RDD, Moderator
Renée Rooijmans – RDD, Moderator


The programmers of the International Rooftop Knowledge Day opened the afternoon’s activities with a warm welcome, introducing themselves and their personal connections to rooftops. Renée Rooijmans is a psycho-anthropologist and rooftop advocate who has lived and worked on rooftops, including Rotterdam’s own Hofbogen. Bas Mastboom is the General Producer of the Rooftop Walk, and Sophie Stravens studied architecture, and theatre. For Rooftop Days, she combined these two passions in a performance “Once Upon a Rooftop” above the Shell Building during the festival weekend. 

Thereafter, Barbara Luns Director of AIR and Rotterdam Architecture Month and Léon van Geest shared their thoughts on the alignment between the two festivals: Rotterdam Architecture Month and Rooftop Days. 

The tectonic and programmatic synergy between Rotterdam Rooftop Days and Rotterdam Architecture Month 

Not such an unlikely combination of incentives, given than rooftops are part of any watertight built structure, Barbara and Léon both emphasized how closely AIR and RDD worked this year to amplify and enhance the possibilities of rooftops in the Rooftop Walk, Het Podium programming, and complementary exhibition programming at Het Nieuwe Instituut, drawing attention to the need to mobilise more concerted efforts to addressing the challenges of densifying cities and exploring new ways to live with finite built and spatial resources.

When queried about AIR’s incentive in aligning the festival with Rotterdam Architecture Month, Barbara asserted that AIR’s imperative of late is understanding “how you densify the city and make use of extra space that’s not used, to its full potential.” 

Last year, from a broadcast location several levels below ground in a parking garage, the festival explored the connection between the different layers of the city and the means by which these layers can be connected to take advantage of higher city elevations as a means of increasing density. Discussions also surrounded the layering strategy necessary to ensure the right degree of urban intensities to make urban communities liveable and relevant to the needs of their inhabitants.  

This year’s event clearly emphasized diverse potentials for rooftop occupation across its diverse rooftop locations, and Léon spoke to the ever-evolving iterations of the festival, describing how with each passing year, the festival enhances its offer and introduces “more layers of possibilities… new territories, challenging insurances, and permitting on a whole new level,” as RDD involves more and more organisations in order to broaden the scope and make rooftop occupation a normal, realisable part of city building.

Capturing and communicating ‘that rooftop feeling’

An essential part of drawing people to the rooftops and generating enough fervour and enthusiasm to collectively tackle these challenges and pursue rooftop living opportunities, is ensuring that enough members of the public experience what RDD describes as ‘that rooftop feeling’ – that intangible elation of being both a part of, and being in a place apart from the hustle of the city. Through the Rooftop Days festival, visitors both gain new perspectives, and find a retreat. Barbara and Léon spoke to their respective organisations’ strategy for stoking this desire in the public’s imaginations through the alignment of their ambitions. 

Barbara drew attention to the way that being on rooftops encourages visitors to take “some distance from what is going on in the city, gaining a new perspective, and observing how the city is developing,” and how important rooftops are to seeing the wider context of the forces of city building at play on the ground, or “social” level. She suggests that the rooftop feeling engenders a greater understanding of, and greater connection to the city. 

Léon reiterated RDD’s ambition for the ‘rooftop feeling’ to be commonplace, that he hopes it will become “normal to be on a rooftop… normal to experience that feeling of exaltation.” Beyond an inspiring feeling, something which is so deeply embedded in the Rooftop Day programme is the belief that roofs are the public spaces of the skies, “not just for a few people, but a great place for everyone.” 

Building on Léon and Barbara’s discussion, this year’s installment of Rotterdam Rooftop Days’ International Knowledge Day’s plenary sessions took the conversation to new heights to explore possibilities from a technical, social, and policy level, and later, to the realm of speculative futures. 

Go tell it on The Podium: Rooftop activation and evangelism

On stage

Olga Wagenaar – Development Manager, Amvest
Urias Santos Bakker – Director Maintenance & Development, Havensteder
Jan Henk Tigelaar – Director, Rooftop Revolution
Sophie Stravens – RDD, Moderator
Renée Rooijmans – RDD, Moderator


With Sophie and Renée moderating, Olga Wagenaar, Development Manager at Amvest property development and investment, as well as Urius Santos Bakker, Director of social housing developer, Havensteder, and Director of Rooftop Revolution, Jan Henk Tigelaar, took the stage to discuss cultivating ‘that rooftop feeling’ in real projects, while balancing real life constraints of returns on investment, building codes, municipal bylaws, sustainability requirements, and simply building enough affordable houses in increasingly crowded cities.  

On integrating the ‘rooftop feeling’ in new developments

Assembled on the stage for the first session were these key stakeholders in city development, each with their own discrete challenge in implementing rooftop as occupiable space in new developments. The good news for rooftops is that each party expressed a desire and commitment to advocating for rooftop use in their projects, whilst drilling down on the hurdles that must be overcome to make rooftop activation commonplace. 

Olga shared that when developing projects, Amvest takes care to look outside the building, [see] what’s happening on the ground level, and think in terms of the short and long run… understand where people want to live and work… we’re also looking at what we can do on roofs. Roofs present nice opportunities for new buildings in the city.”

Havensteder, a social housing developer that owns and operates over 45 thousand homes in the City of Rotterdam struggles “to connect affordability and availability,” says Urius. “If we have to choose between spending money on making green roofs or building more homes, the choice for us is easy, at the same time we want to help solve these challenges. So, we’re putting solar panels on our roofs… 20% of our homes. The business case is easier for solar panels on roofs, but we’re inspired by how we can pursue alternatives, open them up, and give them back to the people.”  

Part of an organization dedicated to advocating for rooftop development, Jan Henk advocacy is somewhat less complicated, as he explained that Rooftop Revolution’s singular intent is “to put Rotterdam at the forefront, and explore and make visible all the possibilities” for rooftops in the city. He added that, “A rooftop walk is such a great thing. It puts 100 thousand people in touch with that[rooftop] feeling,” making the case for rooftops ever stronger.

On building the business case

While the desire to utilise rooftops in new developments and building retrofits may be there, realistically, the most influential factor is the financial question. Olga cited a current project in Delft – a factory retrofit – in which they are trying to make “a good public space for people who will live and work there,” and they want to do something with the roofs, but are “in the phase where it gets technical,” where they have to “think differently about ownership,” and sharing roof spaces amongst owners. This requires a novel approach, and she concedes that can be difficult to implement in current systems, but it’s not impossible. 

As a social housing developer, Urius is faced with balancing different imperatives of very real challenges of climate change and creating enough affordable housing units in the city. He maintains that sustainability objectives “should be combined with other goals… wicked problems constantly emerge and we need to look at alternatives, like if you’re not using roofs for solar panels, do something else, or pay if you’re not making use of the space.”

Jan Henk further asserted that to build the business case for roofs amidst numerous, mounting challenges, “we have to create circumstances as a society to combine all these solutions together. To do this, we have to dive into the complexity and look for solutions that help each other, instead of fixing one problem and ignoring the other.”

On heralding the call: three concrete steps to making the rooftop feeling a reality

All three guests shared the resounding conclusion that to make rooftop use a reality, public opinion has to shift, and to do that, we must “continue the conversation, show [the public] the possibilities, and help them dream about what is possible,” said Jan Henk. Olga echoed this, underlining the need for “rooftop believers” to “spread the word forward.” Urius offered the practical suggestion that we must “create technical solutions for social housing corporations. Make it easier to have multiple uses for roofs, and keep doing the good work. This is the future!”

Small seeds, big dreams: Rooftop initiatives growing from the ground up 

On stage

Laurens van der Wal – Rooftop Village
Sebastian van Kints – Rooftop Village
Miriam Slob – Rooftop Rumour
Sophie Stravens – RDD, Moderator
Renée Rooijmans – RDD, Moderator


Next on the podium were Laurens van der Wal and Sebastian van Kints of Rooftop Village, a Rotterdam initiative for rooftop living, as well as Miriam Slob representing her innovative Tilburg rooftop initiative, Rooftop Rumour. Reflecting on the trials and tribulations of getting a small idea started, the three took the audience through the challenges they have faced in gaining municipal, financial backing as well as spatial opportunities upon which to grow the seedlings of their ideas.

On planting the seeds

Laurens explained that the concept for Rooftop Village “began when we were studying architecture, and of course thinking about how the city should become greener, while also addressing the housing shortage.” He added that “living in Rotterdam we see so much black roof space. Thinking about it, the business case for using roofs is really one plus one equals three… we need to look into symbiosis in our models.”

Sebastian elaborated that for Rooftop Village “it’s been quite a long path. We’re still expecting to hear at any moment if we can do it.” Commenting on the value of cultivating the rooftop experience in cities, he added “from the rooftop you’re super embedded in the city. You don’t see a car, but you see a stream of traffic, and not a light, but an entire block lighting up. The rooftop walk is an urban tribal experience… there’s no place you can experience a city like this except on roofs. It’s a super unique place.” It is clear that an investment in the intangible value of rooftop living and the experience it affords is integral to making the dream a practical reality, and fueling the dedication, in spite of the many obstacles to implementation.

Miriam’s experience reinforces this idea, as her project, Rooftop Rumour, a rooftop farming concept for Tilburg, is still in its infancy, but is making remarkable progress in spite of the fact that it has largely been based on a compelling illustration. She emphasised that selling the dream implies telling “a story to the people we want to reach.” With the render of her dream “a rooftop owner reached out – the owner of the old V&D building in the heart of the city. The image got people excited.” 

On staring down challenges

Facilitating buy-in from key stakeholders (owners, municipalities, the public) is complicated. Laurens conceded that “there are so many extra questions, rules and regulations, and then having to wait for the municipality to say whether the permit has been approved,” but that he’s experienced enthusiasm and a cooperative spirit working with Rotterdam’s municipality, where “instead of just handing something in and getting a judgement, they’ve [the municipality] been thinking alongside us.” He added that “this needs to happen more often,” and that impediments exist in outdated standards, and siloed departments that weigh down the process, making approvals more complicated to achieve.

Miriam also expressed some exasperation, and offered that “the city could move faster,” querying “why am I still the only one doing this [in Tilburg].” She pointed to the essential role of the municipality in advocating for rooftop development at a policy and procedural level.   

On heralding the call: three concrete steps to mobilising rooftop initiatives

As these rooftop pioneers grow their dreams from the ground up, the advice they offered in the discussion to propel the movement, and change both public and policy conventions, largely concerned the imperative to make rooftop activation the norm. For Sebastian, this means creating “a new vocabulary, and new norms, new names. Building on an existing building is a different game so we need to create precedents. The process will go faster in future, and sharing this knowledge will make the next tasks easier.” 

Laurens offered “can we create databases with information about how others have solved problems? With a database you can see where there are opportunities.” He emphasised the need to build and catalogue knowledge from past experience, so that initiatives that follow need not start from square one, but can iterate on past advancements.

Miriam candidly stated “I don’t say this with disrespect, but why is this still special?” This summed up the conversation in its simplicity, circling back to the specialness of the rooftop feeling, which, though the imperative of the festival and initiatives such as Rooftop Village and Rooftop Rumour will ideally result in making rooftop living more conventional; however, let’s hope the rooftop feeling never dissipates. 

The cross-border rooftop reformation 

On stage

Heleen Vanden Bergh (City of Antwerp, Cultural Department)
Bruno Inácio (Faro)
Paul van Roosmalen (Rotterdam)
Sophie Stravens – RDD, Moderator
Renée Rooijmans – RDD, Moderator


Following the top down incentives of developers, and the ground up incentives of rooftop pioneers, Sophie and Renée welcomed municipal influencers from the cities of Faro, Antwerp, and Rotterdam to the stage. They provided insights into how they have been approaching advocacy for rooftop use in their own domains: the challenges, the strategy, and the progress they’ve made. 

On getting started: Raising the roof[top] concept within different international municipal contexts

A rooftop advocate in Antwerp, Heleen described how they began, stating that “some colleagues in sustainability were inspired by Rotterdam’s Rooftop Days, and in 2018, they asked me to organise the first rooftop festival.” In 2020, this resulted in a major festival involving 45 roofs, and is now spearheaded by the cultural department. Demonstrating that festivals such as Rotterdam’s Rooftop Days are influential in building momentum and spreading awareness.

Like Rotterdam, Faro faces growing pains with tourism and gentrification, so Bruno described that when the cultural department puzzled as to how they could start to redefine city identity and face the problem of overcrowding, rooftops became a plausible frontier. They “had the idea of a rooftop festival… started benchmarking, and involving colleagues from other areas.” He further conceded that they didn’t want rooftop activation to fall within the domain of the cultural and creative departments, but rather see the benefit of advocating for them from a “bigger, wider, and broader” reach within the city since their realisation involves so many different domains.

In Rotterdam, Paul shared, it “started 15 years ago with green roofs, and bringing nature back to the city.” He admits that “solar panels have displaced green roofs, but we still need to do green and water buffering,” so, now with rooftop living, the city is faced with the challenge of trying to do it all. 

“Can’t we do it all?” Paul asked, “and do it in an integral way?” 

On transforming the dream to reality

The ambition is one thing, but making the dream real and tangible for the public is another. Paul explained that in Rotterdam, the initiative just had to start. He explained, “seven years ago we began. We had a day, but we didn’t have knowledge. You have to start somewhere and go with enthusiasm.” He later expanded on this notion of seeding ideas and mobilising transitions by explaining that “transitions take 20-50 years. They’re also something you cannot manage. You can push them, and encourage things to build up, like enthusiasm in the small scale.” It’s clear that the change will not occur overnight, but the implementation of micro activities at different scales, from private rooftops, to rooftop walks, will ultimately create a tidal shift. 

Bruno commented on how every part has a role to play in mobilising. He explained that “there’s a tension between people who dream it and want to do it… everyone has a role, and it’s very important to have that tension. If you don’t, you don’t go forward. We need to see each other as partners, and influence each other from the inside to make it move.”

For Heleen, she bemused that she’s “a lonesome cowboy in the city” and relies on an advisory board, permits, urban planning…to get work done.” She described the conditions in Antwerp being such that there is a great deal that can be done with some “1000 buildings that the city owns, including 350 schools,” but that currently the work is in the visioning stage, and in preparing, and aligning incentives of sustainability and climate proofing for coming legislation. For Heleen it seems, the transformative work requires strategy and alignment – in the plan before the jump. 

On heralding the call: taking responsibility for change

To take change in hand and influence what you can, Paul argued that “it’s about building an ecosystem,” suggesting that festivals play an integral role in knowledge generation and breaking through the “silo thinking.” 

Bruno advanced the idea of spreading the “ownership of the movement.” “Let people do it, let people try,” he said, “having a lot of fathers and mothers for the same idea is important… the pioneers, the dreamers, and the guy in the fire department. He needs to be the father of an idea.”

Heleen echoed Bruno’s call for collective mobilisation, impelling experts to climb “their way up the ladder to their managers,” and convince them to support the initiative and make necessary changes possible to advance the concepts within their own departments. 

Rooftop Hero 2022

Just before the break, Leon van Geest leaped to the stage to announce the 2022 Rooftop Hero Award winner, none other than Miriam Slob for Tilburg’s Rooftop Rumour, who, though early in the process, has made incredible gains in acquiring a rooftop for her plans, and is taking responsibility for the idea within the realm of her own influence: identifying a need, and taking steps to address it.     

Take me to church: A rooftop conversion story

On stage

Arman Jeddi (Hamburg University)
Felix Gorrissen (Hamburg University)
Leonie Schleyer (Hamburg University)
Sophie Stravens – RDD, Moderator
Renée Rooijmans – RDD, Moderator


Following the rooftop frontrunners in European municipalities, Renée and Sophie welcomed three architecture students from the University of Hamburg to the stage who shared their concept for Garten Eden, the conversion of St. Katharinen Church’s rooftops in Hamburg. As a centrepiece in the city, and an icon of Western architecture, it has incredible potential as a demonstration of what is possible with rooftops.

On the concept of Garten Eden

A short video presentation from the students walked the audience through the incentive for the project, citing the need for social retreats from an increasingly dense, and consumption-oriented Hamburg city centre. Aside from providing functional social space, the project also has ambition to spread awareness, hence the site of its intervention: a church sat beside an active city square. The church’s rooftop intervention, involving both the roof of the church itself and the adjacent community centre, placing solar panels on the sloped roof, and a green terrace on the roof of the community centre. New elements speak the same language of the old to reinforce the church’s existing iconic qualities, while articulating nature’s role in this new version of the church’s role.

On being both climate-friendly and socially active 

The team explained that solar panels on the roof satisfy power demands for the church, and surrounding households, while the flat roof of the adjacent community centre provides a “flourishing retreat,”made accessible through a set of public stairs that circle around an existing tree in the church’s courtyard.  

On the next steps

Team member Arman Jeddi maintained that the concept’s ideas are very much alive and the “rooftop ambitions are still there. We’re working with the current priest – a very cool guy – who’s trying to turn his church into a climate church and rethink this conservative structure. If we push more, this could one day be a reality.”

Catalysing the rooftop commons 

Conceptualizing and democratising the ‘rooftop feeling’

On stage

Dr. Helen Toxopeus
Jacintha Scheerder
Katrina Johnston-Zimmerman
Sophie Stravens – RDD, Moderator
Renée Rooijmans – RDD, Moderator


For the final panel discussion of Rooftop Knowledge Day 2022, Renée and Sophie welcomed Katrina Johnson-Zimmerman, Urban Anthropologist, Dr. Helen Toxopeus, lecturer in Economics at the University of Utrecht, and Futurologist Jacintha Scheerder, founder of We the Future. The lively discussion traveled many different paths through time and space, across anthropology, sustainable economics, and storytelling, stirring the imagination with the possibilities that lie ahead if we only work together, and undertake initiatives both big and small. The afternoon concluded with explorers pursuing even more intangible rooftop feelings with an ephemeral brew created by distiller, Meidi of Floret Atelier, tasting the ‘rooftop feeling’, and concluding with a short dance performed by Ilja Geelen, and filmed by Yassine Abouhamid, in which Geelen dances the experience of her rooftop in Morocco, translating the ‘rooftop feeling’ kinetically.   

On understanding where we come from to know where we’re going (Katrina)

Katrina of THINK.urban opened the discussion with the perspective that in order to think about where we’re going, we have to look at the past, in our earliest cities like Catal Huyuk in Turkey, which had no streets, no parks, and where rooftops are the principal public means of moving through the settlement. Katrina asserted that what was critical about this ancient city, was that its inhabitants “understood the shared space of rooftops as a community,” and advocacy for new futures lies in seeing the city “as a habitat,” and a “community.”   

On creating public good together (Helen)

With a PhD in finance for sustainable innovation, and head of the Sustainable Finance Lab, Dr. Helen Toxopeus lends her strength in economics to the rooftop question, underlining that to make rooftop activation commonplace and a normal part of city building, we “need a collective business case, as a singular actor looks at the numbers, sees the costs, and realises that the benefit doesn’t provide the financial return.” She emphasized that “if you invest together, you reap the benefits,” citing Hamburg’s special tax constructions for green roofs, among others, for shifting the weights to create wins for different stakeholders, and make rooftops activation a real city implementation.

On considering changing norms and values (Jacintha)

Futurologist Jacintha Scheerder of WE THE FUTURE shared her research with ‘Let it Grow’ in which she explored how to cultivate green living urban futures, and pondered the role green can have in cities. She cited all manner of different benefits of green from both inside and outside the box, emphasizing that the greatest benefits are often the most intangible, and difficult to quantify.  

On who will pay for it

Amidst all this talk of the value of the “rooftop feeling” and making it available to the masses, the obvious question emerged time and time again: but who will pay for it? Helen countered that “The Dutch bank is beginning to translate external things into asset values, like loss of biodiversity, climate change. According to investment criteria, you have more green lights if you’ve thought about a green roof in this way. Thinking about these makes a strong case.” 

Jacintha offered a more draconian, but irrefutable strategy: “you need to pay if you don’t use your roof. There’s your money. We need more force at a governmental, and national level, it’s up to municipalities to put a tax on empty roofs.”

On heralding the call

Underpinning the broad territory of the conversation was the notion of collectivity and collaboration and a pervasive belief that we don’t get very far without working together to solve the present challenges. For Katrina, this implies that “to get to a place to make change, we need to develop trust… with a shared vision before we start moving toward something together.” 

For Jacintha, the question involves a paradigm shift in values, not seeing roofs simply as “shelter,” but rather valuing them for the multitude of other positive impacts they can have in the city, and asked, “how do we value that in the city?”

Pondering the critical mass of activations required to make “catalytic change,” Helen underlined the need to be working at multiple levels “happening at the same time, then momentum, then the shift.” She emphasized focusing on what you can do to drive change, reminding us all that to avoid despairing, “work on your circle of influence, and what you can do from there… work on growing influence from your specific position” to contribute to the momentum and drive positive change. 

It is easy to despair and do nothing, but as Katrina, in a final rallying call articulated, “pessimism is a synonym for laziness,” emphasizing that collective action is the call, “we just have to do it.”