Rooftops: Underutilized treasure
5' read - published October, 13th 2023
In the midst of a global space scarcity crisis, a pressing question arises: Why do we find ourselves contending with overcrowded cities, a shortage of affordable housing, limited access to valuable public spaces, and renewable energy sources when there is for example abundant unused space on water, as demonstrated by the floating neighborhood Schoonschip, and right above our highways, as exemplified by the Swiss energy peer?
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Another hidden treasure are rooftops, not only to enhance the value of buildings but also enrich the communities that surround them. Imagine if our cities not only provided land development plans but also comprehensive rooftop utilization plans, breathing new life into these often barren spaces. This raises a crucial question: What should these rooftop plans include, and what myriad of uses can we envision for this uncharted urban territory?
Sustainability: Energy generation, cooling down and water collection
Energy generation
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According to ZHAW in Zürich, Switzerland has the potential to entirely replace its atomic power plants with solar energy, harnessing just 26% of its existing rooftop surface (644km²)(1). Remarkably, as of September 8, 2022, only 2.5% of Switzerland's vast rooftop area had been utilised for solar energy generation. Canton de Vaud took this to heart in August 2023 with it’s six-pillar plan aimed at achieving carbon neutrality by 2050, by maximising rooftop coverage with photovoltaic panels on new buildings and renovations by 2040(2).
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In the realm of innovative solar technologies, several groundbreaking solutions are changing the landscape of renewable energy. Solskins solar modules are designed to meticulously track the sun's path, optimizing energy generation throughout the day. For structures with curved roof surfaces or flexible constructions, Solar cloth offers a versatile and efficient solar energy solution.
PowerNEST takes solar energy generation to the next level by combining traditional solar panels with vertical blade wind turbines, resulting in an impressive sixfold increase in energy production compared to solar panels alone.
Ubiquitous Energy has introduced fully transparent PV modules, a breakthrough that allows skylights to serve a dual purpose, providing natural light while generating electricity. Even historic buildings can join the sustainable energy movement by replacing conventional roof tiles with Freesuns solar tiles, contributing to clean energy generation.
While conventional solar panels generate electricity exclusively during daylight hours and are less efficient under cloudy conditions, recent innovations are reshaping the landscape of solar energy. Engineers at Stanford University have developed night solar panels that can generate electricity even after the sun has set. Additionally, Hybrid solar panels created at Soochow University are capable of harnessing energy from raindrops. These groundbreaking advancements lay the foundation for uninterrupted electricity generation, regardless of overcast skies or nighttime conditions.
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Cooling down - heat island effect
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According to the national center for climate services the temperature difference between the city and the surrounding rural area can reach up to 6 degrees in Switzerland(3). As the surfaces of buildings closest to the sun, roofs can also serve as a means to protect structures from overheating and mitigate the urban heat island effect. In Utrecht, Netherlands, all bus stop roofs are being greened, allowing for evaporative cooling. Green roof temperatures can be 30–40°F (16-21°C) lower than those of conventional roofs and can reduce city-wide ambient temperatures by up to 5°F (2,7°C)(4). Another method used to cool buildings is applying ultra-white paint, which can reflect up to 98.1% of sunlight.
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Water retention - collection
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European regions are increasingly susceptible to flooding due to climate change and increased pavement in recent years(5). Therefore, it is important to consider water management in urban areas. The 'De Boel' project in Amsterdam has implemented Polder roofs to store rainwater, treating it as a resource rather than waste. In addition to this, it eases the burden on the sewage system.
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It's worth noting that green roof solutions also enhance biodiversity. Additionally, research has shown that combining a green roof with PV panels is beneficial for energy production, as the greenery helps cool down the panels. For sloped rooftops, mygreentop has designed green tiles, making rooftop greening possible on slopes ranging from 20 to 60 degrees.
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This raises the question: Should we dedicate roofs to energy generation, cooling or water retention? The Dutch company Rooftop Revolution have pioneered the creation of Sustainable Roof Opportunity Maps, offering a visual representation that takes into account building characteristics, environmental factors, and area analysis. These maps empower municipalities and real estate stakeholders to identify the most viable and advantageous uses for rooftops, including water storage, energy generation and urban cooling.
Commercial, recreational, cultural, community uses
Rooftops not only offer great views but are also visible, making them valuable both for human usage of the roof and for marketing purposes that are visible from a distance. Often, rooftops are transformed into commercial spaces such as restaurants (DeDAKKAS), bars (Park bar) and event venues.
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Stimulating destination areas can emerge, as seen with the Over the rainbow in Changsha, China. In dense urban environments, rooftops can serve as public spaces and community gathering areas. This can be achieved with recreational areas like Miyashita Park or a skater park (H.A.N.D.S), or even a large public park like the Shenzen skypark, which covers a 1.2km rooftop above a metro station.
Remarkably, a building can serve two completely opposite purposes, as demonstrated by the Copenhill waste-to-energy plant in Copenhagen, which also functions as a ski slope. On their way up “the mountain”, people even get the chance to see inside the power plant.
Renovations and extensions, flexible rooftops
Apart from renovating rooftops with solar panels and adding community features, greenhouses (e.g. Lufa farms) provide another potential use. This not only provides additional space for residents but can also serve as an educational tool for the community. Moreover, rooftop greenhouses can be integrated with other functions. For instance, the excess heat generated by the cooling system of the Wind Cloud servers supports the growth of CO2-absorbing algae in a rooftop greenhouse. Similarly, the Symbiose project aims to harness rooftop solar potential by installing bioclimatic greenhouses that capture energy, pre-heat domestic hot water, and create new spaces for residents.
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Extensions often encounter local regulations, making the process complex but not impossible, as demonstrated by the Factory houses, which managed to construct housing on top of industrial buildings in an exclusively industrial area. Another example for a vertical extension is the De Zinnekes school, in Brussels. Located in a dense area and facing space constraints, architects decided to add an extension to the flat roof of the existing building, allowing for a creche to be featured on top of the school.
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Also, roofs don't always need to be static. The Umbrella mosque in Medina includes 250 huge sunshades, forming a roof that covers more than 156 000 m². This illustrates the existence of flexible roofing solutions, which also allow for testing roof constructions before permanent installation.
The world of urban development is looking up – quite literally. Rooftops, often overlooked and underutilized, hold immense potential to address the challenges of our crowded cities. Rooftops offer more than just energy generation opportunities and rooftops are no longer hidden spaces but dynamic canvases for innovation, sustainability, and community enrichment. As we look up, we see boundless possibilities in the skies above, a new frontier in urban development that promises a brighter, more sustainable future.
(1) Source: NZZ, Muss bald jedes Dach ein Solardach sein?, September, 9th 2022.
(2) Source: État de Vaud, Consultation sur la nouvelle loi sur l’énergie, August, 21st 2023.
(3) Source: NCCS, Climate change in cities, March, 28th 2023.
(4) Source: General Services Administration, The Benefits and Challenges of Green Roofs on Public and Commercial Buildings, 2011.
(5) Source: European commission, New analysis indicates European cities and countries with highest expected losses from future flooding, June, 21st 2023.