In increasingly denser urban environments, there is a new-found interest in underused spaces as opportunities for further development. Representing up to 25% of cities' land area, rooftops are among the most exciting spatial resources. From sustainable infrastructure and urban farming to social spaces and cultural venues, the article looks into the potential of creating a multi-layered city through the activation of urban rooftops.
There are several types of untapped spatial potential, from gaps within the urban fabric to residual public spaces. Still, an aerial view of any city centre uncovers the roofscape as a significant underused surface. Searching beyond penthouses and private extensions, urban roofs have already entered the conversation surrounding both urban densification and climate resiliency. Moreover, as the pandemic underlined a severe need for more outdoor areas, rooftops are regarded as a viable addition to the public space.
With the introduction of roof sealants, the flat roof became a staple of Modern architecture, but the excitement over the technological feat overshadowed the inquires into its architectural potential. With few exceptions, such as the roof landscape of Le Corbusier's Unité d'Habitation envisioned as space for children to play, or Giacomo Mattè-Trucco's Fiat Lingotto Factory in Turin featuring a rooftop racetrack, Modernism's legacy in Europe amounted to vast expanses of inconsequential flat roofs. It wasn't until the 1990s that the roof began to be seen as more than an enclosure, but as an integral part of the project's spatial concept and program, as both architects and developers begin to realize the missed opportunity of an inaccessible, purely technical roof. From Mecanoo's trailblazing green roof at TU Delft more than two decades old to JAJA Architects' playground above a car park or BIG's ski slope on top of the CopenHill, the roof has become a subversive tool for transforming the experience of the city.
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New Recreational Spaces
However, the existing rooftops hold the most significant potential in creating a multi-layered, hyper-connected urban environment. Referring to the 2016 Stairs of Kriterion installation, MVRDV's Winy Mass argues for the use of the 5th facade as means to expand the public space: "we show what this city could look like if we do that in many places, engaging a series of our existing buildings and giving access to their roofs, to create a new, much more interactive, three dimensional and denser urban topography for the next city generation". The studio has flirted with the idea of activating rooftops on several other occasions. For the If Factory renovation project, the studio adds a green bamboo landscape on the roof, packed with activities and accessible through a public staircase.
Similarly, officePROJECT's refurbishment project YOU+International Youth Community Shenzhen adds shared amenities on the two existing roof terraces, while ZHUBO DESIGN's Green Cloud creates a multi-layered communal space above a residential building. Another example of converting the city's upper layer into an extension of the public space is Rotterdam's park on top of the former railway station Hofbogen. The place is the setting of film screenings and dance performances, in addition to being a popular public garden.
An Opportunity for Sustainable Infrastructure
Existing rooftops are most commonly put to good use through green roof systems, urban farming or the installation of energy production and water management systems. In particular, living roofs hold a diverse array of benefits, as they capture stormwater runoff, improve air quality, help mitigate urban heat-island effects, and even contribute to the preservation of biodiversity by providing habitats for bees and birds.
Green roofs have been mandatory for newly constructed buildings in Copenhagen since 2010, and France requires living roofs or solar panels on the roofs of new buildings since 2015. However, Barcelona is pushing for a re-evaluation of the existing rooftops to deploy sustainability infrastructure across the city and build a more resilient urban environment. The municipality produced a guide helping residents create different types of green roofs in a city with an already established tradition of using flat roofs for both practical and recreational purposes. Moreover, rooftops might also hold the future for urban farming, as more and more projects pop up across Europe with promising results in catering to residents and restaurants.
For several years now, different initiatives and events have made the general public more aware of this untapped resource for expanding the public space. ROEF Amsterdam is a festival that takes place across several rooftops, allowing dwellers to experience the city differently while also contributing to Amsterdam's roofscape transformation. Similarly, for this year's Melbourne Design Week, John Wardle Architects and Finding Infinity created a rooftop infrastructure for solar power that doubles as a space for socialization. The project expands on Melbourne's rooftop culture while also promoting sustainable energy.
Finally, although unrelated to public space, it is worth mentioning that existing rooftops are also speculated upon as potential solutions to the housing crisis in dense cities. London Municipality has been considering rooftop extensions at a large, coordinated scale for some time now to help alleviate the housing shortage. However, opinions on the endeavour's feasibility are divided, and built case studies are yet to be seen.
Activating existing urban rooftops poses a series of challenges, from accessibility, additional loads on the existing structure to ownership and maintenance. However, the densification of cities prompts architects, dwellers and developers to envision roofscapes as the next frontier in urban transformation.