05.02.2026

Cooling Strategies for Urban Roofs – Technical, Design, and Legal Aspects

Building design

The green roof stands for innovative cooling solutions and sustainable urban design.

Hot cities, overheated roofs—and the search for cooling solutions that go beyond a coat of white paint: Urban roofs have long been a playground for climate engineers, designers, and legal experts alike. But cooling isn’t magic—it’s the result of sophisticated technology, creative planning, and a clear legal framework. Anyone shaping cities today must master the cooling principles for urban roofs. How can technology, design, and law work together effectively? Welcome to a journey through the city’s future cool hotspots.

Definition and Relevance of Cooling Principles for Urban Roofs in the Context of Climate Change
Technical Solutions: Green Roofs, Reflective Systems, Evaporative Cooling, Innovative Materials
Design Challenges and Potential for the Cityscape and Quality of Life
Legal Framework: Building Codes, Funding, Standards, and Obstacles
Interactions between roof use, urban climate, and energy efficiency
Best-practice examples from Germany, Austria, and Switzerland
Risks, side effects, and conflicting objectives in roof cooling
Strategies for Integration into Sustainable Urban Planning and Architecture
Future Prospects: Smart Roofs, Digital Control, and the Role of Research and Policy

Cooling Concepts for Urban Roofs: Significance, Fundamentals, and Challenges

Anyone strolling through the cities of Central Europe in the summer quickly realizes that roofs are more than just protection from the rain. They are heat shields, energy storage systems, and—unfortunately—sometimes even ovens. Climate change is hitting urban spaces with full force—and here, in particular, the surfaces that are mercilessly exposed to the sun. Roofs in particular—from flat to sloped—are becoming key players in the fight against urban overheating. But what does “cooling logic” actually mean? At its core, it involves the targeted management of solar radiation, heat storage and dissipation, and moisture balance to actively regulate the temperature in and around buildings. These strategies range from passive measures such as greening to technical systems and innovations in materials technology.

The challenge is multifaceted. Cities are growing, space is becoming scarce, and density is increasing—traditional green spaces can no longer compensate for heat gain on their own. This is where roofs, as a previously underutilized resource, come into focus. They offer potential for more than just a few solar panels. They can mitigate heat islands, provide evaporative cooling, create habitats, improve rainwater management, and even serve as social spaces. But every roof surface is different: structural integrity, use, orientation, surroundings, and local climate conditions determine which cooling approach makes sense.

Scientists agree: Without the systematic integration of roof cooling, cities will become uninhabitable due to extreme heat in the long term. Studies show that targeted greening and reflectivity on roofs can significantly lower ambient temperatures and mitigate the urban heat island effect. At the same time, cooling is not an end in itself, but rather part of a holistic strategy for sustainable, livable cities. Yet implementation is particularly complex in Germany, Austria, and Switzerland—caught between technological enthusiasm, design aspirations, and legal gray areas.

A key problem is the lack of coordination between planners, developers, property owners, and authorities. Often, these stakeholders operate in parallel rather than collaboratively. The result: half-baked solutions, inefficient investments, and wasted potential. Anyone who wants to cool cities successfully today must not only understand technology but also consider design and legal considerations. The requirements range from thermodynamic expertise to knowledge of plants and legal finesse. Only through collaboration can the “cool city” emerge.

The question of the optimal cooling strategy is always context-dependent. There is no one-size-fits-all solution, but rather a modular system of methods that must be combined on a case-by-case basis. Those who ignore this risk costly misinvestments and frustration among owners and users. At the same time, great opportunities are opening up: Those who plan correctly now will not only alleviate climate stress but also enhance entire neighborhoods—and bring urban planning into the 21st century.

Technical Solutions: From Green Roofs to Smart Roof Covers

The technology of roof cooling is a science in its own right—and a playground for innovation. The best-known examples are green roofs, which generate evaporative cooling through plants and substrates. The plants absorb water from the substrate and release it into the environment through their leaves. This process lowers the surface temperature—sometimes dramatically—traps particulate matter, and improves the microclimate. Intensive green roofs with perennials and small shrubs provide significantly more cooling than thin, extensive green roofs. However, as the layer thickness increases, so do the structural and maintenance requirements.

Another technical approach is reflection. Light-colored, highly reflective coatings—so-called “cool roofs”—reflect a large portion of solar radiation back into space instead of converting it into heat. Modern coatings achieve reflectance levels of over 80 percent. This can lower the surface temperature by 20 to 30 degrees compared to conventional bitumen roofs. The effect is particularly pronounced during hot summers and on large flat roofs, such as those on commercial buildings or schools.

Systems that specifically use water are also innovative. In evaporative cooling, water is applied to the roof surface, where it evaporates and draws heat away from the surroundings. The principle works similarly to the skin’s natural cooling through sweating—only on a large scale. Technologies range from open water reservoirs and misting systems to smart storage solutions that temporarily store rainwater and release it as needed on hot days. Control is increasingly digital and temperature-regulated.

Material innovations also play a role. Novel membranes, ceramic surfaces, or so-called phase-change materials (PCM) can absorb heat and release it again after a delay. This helps buffer temperature spikes and reduce the operating time of air conditioning systems. Particularly exciting are combined systems in which greenery, reflection, and water management work together intelligently. Researchers are already working on multifunctional roof structures that automatically adapt to weather conditions.

But technology alone is never the solution. The best roof cooling only works if it is tailored to the specific building, its use, and its surroundings. Structural engineering, fire safety, roof pitch, accessibility, user preferences, and maintenance requirements all help determine which systems are realistic and cost-effective. This highlights that the gold standard is hybrid solutions that combine technology, ecology, and user needs—all embedded in an overarching concept for the urban climate.

The Design Dimension: Cooling, Cityscape, and Quality of Life

Technical efficiency is one thing—but roofs have long since become design statements as well. The integration of cooling systems must therefore be guided by the cityscape, the architecture, and the needs of urban society. Green roofs, for example, are not only a climate protection measure but also a space for experiences: They offer bees, birds, and people new habitats, create green oases in the midst of the concrete jungle, and promote biodiversity. In densely populated neighborhoods, they are often the only place where nature remains visible and accessible. Designs range from natural meadows to urban gardens to accessible rooftop parks that offer a pleasant environment for people to spend time in.

Reflective roof surfaces are often considered a design challenge—the famous “white roof” isn’t everyone’s cup of tea. Yet with modern coatings, color schemes, and textured surfaces, aesthetic solutions can be found. Architects and designers are challenged to balance reflection and design without turning the cityscape into a blinding desert. Innovative examples show that even “cool” roofs can be beautiful when function and form are cleverly combined.

An important aspect is the visibility of rooftop landscapes. In the past, roofs were purely technical spaces. Today, they are understood as the city’s fifth facade—visible from above, from neighboring buildings, from drones, and increasingly also to the users themselves. This new visibility challenges planners, as every roof solution shapes the cityscape. Integrating cooling systems, solar panels, recreational spaces, and greenery requires creative composition and interdisciplinary collaboration. Those who design boldly in this area set the tone for a new urban lifestyle.

The social dimension should not be underestimated either. Green and cool roofs are places for interaction, relaxation, and community. They improve quality of life and create new spaces for urban gardening, yoga, culture, or play. Especially in densely built-up city centers, they become places of retreat and symbols of identity. Roof cooling therefore also contributes to social sustainability and the strengthening of public space—provided it is conceived with an open mindset and designed to be accessible.

The major challenge remains: How can we successfully integrate innovative cooling concepts into the very fabric of urban design? We need visionaries who think beyond mere technology, and a collaborative effort among architects, engineers, landscape architects, and artists. Only then can we create rooftop landscapes that have a positive impact on the climate, inspire visually, and foster social connections—and truly make the city “cool.”

Legal Framework: Leeway, Obstacles, and Funding Opportunities

Technology and design alone are not enough—without legal clarity, any cooling concept on a roof remains an experiment with an uncertain outcome. Building codes in Germany, Austria, and Switzerland are a tangled web of regulations, standards, and exceptions. Green roofs are subsidized or even mandated in many places, for example in zoning plans, state building codes, or municipal ordinances. At the same time, there are numerous technical standards, such as DIN 18531 for roof waterproofing or the FLL guideline for green roofs. Planners must be familiar with and comply with these requirements; otherwise, they risk having to make corrections, face liability, or lose subsidies.

A key issue is structural engineering. Greenery, water, and technical installations—all of these add weight to the roof. The load-bearing capacity must be verified, fire safety regulations observed, escape routes kept clear, and maintenance ensured. In existing buildings, retrofitting is often possible only with considerable effort. Here, economic feasibility determines whether roof cooling becomes a reality or remains a pipe dream. Subsidy programs from the federal government, the states, and local municipalities offer financial incentives, but the application processes are often complex and bureaucratic. To be eligible for funding, applicants usually must establish a comprehensive verification and monitoring system.

The issue of ownership and use is also legally sensitive. Who is allowed to use the roof? How are costs and benefits allocated? Especially in the case of apartment buildings or commercial properties, coordinating between owners, tenants, neighbors, and property management is often time-consuming. Disputes over access, maintenance, and liability can delay or prevent projects. Clearly defined usage agreements, liability issues, and maintenance obligations are therefore essential. This is the only way to create reliable structures for long-term cooling logic projects.

Another key area involves codes and standards. The technical approval of new materials or systems, compliance with energy-saving regulations, environmental requirements, or urban planning agreements—all of this must be clarified early on. Innovative solutions often encounter regulatory hurdles here because existing standards are not designed for multifunctional roof systems. Those who experiment must therefore expect increased testing and documentation requirements—or actively participate in the further development of regulatory frameworks.

However, the legal complexity should not be a deterrent. On the contrary: it also offers opportunities to set new standards, take advantage of flexibility, and drive development forward. Municipalities that consistently integrate cooling concepts into their bylaws, funding programs, and zoning plans create planning certainty and a climate conducive to innovation. The future belongs to cities that have the courage to set regulations—and that view technology, design, and law as a unified whole.

Perspectives and Best Practices: The Future of Cooling Logic on Urban Roofs

What does the future of cool roofs look like? A look at innovative cities shows that the combination of technology, design, and law opens up new horizons. In Basel, for example, green roofs are mandatory—and the city supports not only their installation but also their maintenance. The result: a network of green oases that measurably improve the microclimate and serve as a model for other municipalities. In Vienna, rooftop parks are being created that use digitally controlled irrigation systems and sensors. Control is handled via apps that compare weather data and water requirements in real time—a prime example of smart cooling logic.

There are also flagship projects in Germany. In Hamburg, multifunctional roofs are being installed on school buildings that combine greening, solar energy, and rainwater management. The projects are part of an urban strategy for climate-resilient neighborhoods—and provide valuable data for further development. Munich is focusing on pilot projects with innovative cooling materials and testing various coating systems in a real-world laboratory. The results are incorporated into urban planning and standards development.

Research and development are driving cooling technology forward. Universities and startups are working on self-healing roof membranes, adaptive greening systems, and the integration of photovoltaics and evaporative cooling into a single system. Digital twins, which are increasingly being used in urban planning, enable the simulation and optimization of roof cooling in real time. This allows different scenarios to be run through and the best solution to be found for each building—a quantum leap compared to the previous trial-and-error method.

Risks and conflicting goals remain: reflective systems can blind neighbors, green roofs increase maintenance requirements, and evaporative cooling consumes water resources. Not every solution makes sense everywhere, and not every roof is suitable for everything. What is crucial is an integrated approach that aligns technology, design, and legal considerations and involves users early on. Participation and communication are key factors for acceptance and success.

The grand vision: The urban roof becomes a multifunctional platform—for climate, energy, biodiversity, recreation, and community. Smart control systems, digital twins, and innovative materials transform the rooftop landscape into a laboratory for the city of the future. Those who invest in cooling strategies now will not only create cooler cities but also attractive, resilient, and livable urban spaces. The era of hot heads is over—the future of the city is now being decided on the rooftops.

Conclusion: Cooling Strategies as the Key to the Climate-Resilient City

Urban rooftops are the new battlegrounds of urban development—and cooling strategies are the set of rules that will determine how livable, resilient, and attractive our cities remain in the future. The fusion of technology, design, and law is not an option but a necessity if we are to avoid overheating, energy waste, and social alienation. Experiences from Germany, Austria, and Switzerland show that those who boldly integrate, think interdisciplinarily, and actively shape the legal framework can achieve far more with rooftop cooling than just a few degrees less on the thermometer. The cool city is no accident, but the result of smart planning, strong alliances, and continuous innovation. Cooling strategies are not a nice-to-have but the new mandatory discipline of urban development—and the best proof that even the hottest roofs have the potential for true coolness. Those who invest in the “fifth facade” now are not only making the city cooler but also better.

22.04.2025

Architecture

44 residential units in Saint-Denis from DREAM

Building design

The new building with 44 residential units by DREAM. Photo: Cyrille Weiner

Two decades after the devastating fire in a dilapidated residential building on Rue Fraizier in Saint-Denis, a new construction project marks a turning point in the urban development of the north of Paris. The Parisian agency DREAM (Dimitri Roussel) has realized a residential ensemble with 44 units there – half for rent, half as subsidized ownership according to the “Bail Réel Solidaire” (BRS) model. It is the first project of its kind in Saint-Denis. However, the ambitious gesture is less about architectural showmanship and more about functional, mass-produced housing that strives for social integration.

The new building stands on a site that has been derelict since the fire in 2001. The fire at the time drastically exposed the dilapidated conditions in the old building, which was being used by shark tenants. The ensuing vacancy was perceived not only as a physical defect, but also as a social one. DREAM now sees the project as a contribution to “repairing” the neighborhood – and to re-establishing trust in the urban space.

The 44 residential units are spread across several buildings and follow a clear principle: as much individuality as possible within the standardized production. Almost all of the apartments are open-plan, with many facing in several directions. The majority have generous outdoor spaces – balconies or gardens at ground level. Interior qualities have also been considered: separate entrance areas with storage space, daylight kitchens that can be closed off if required and large window openings with panoramic views are all part of the repertoire.

The floor plan design is based on the charter of Plaine Commune, the inter-municipal association responsible for the area. The urban positioning of the buildings responds to morphological and climatic analyses of the site. A typical planning response is, for example, the staggering and orientation of the volumes to optimize daylight and natural ventilation.

In terms of design, DREAM dispenses with design experiments. Instead, the architectural expression arises from the materiality and rhythm of the façade. Wooden slats, metal panels and open balcony structures made from a combination of wood and metal structure the outer shell. Great importance was attached to prefabrication: The timber frame construction walls, including cladding, windows and shading elements, were manufactured entirely in the factory. The self-supporting balconies also arrived on site pre-assembled.

This strategy has several advantages: Firstly, it increases the quality of execution, and secondly, it reduces the construction time – a factor that plays a particular role in the densely built-up and socially sensitive Saint-Denis. All in all, the result is a residential building that relies on CO₂-reduced construction methods without playing this off visually.

What is striking about the project is the effort to establish communal zones alongside the private living space – a concept that is often referred to elsewhere as “third places”. In Saint-Denis, the elements are simple but effective: a large, inviting entrance area, green inner courtyards with passageways and roof gardens that serve as places to retreat and meet. The lobbies act as semi-public buffer zones between the street and the apartments. Visual references to the courtyard are intended to provide not only light but also social control.

The whole project was designed in collaboration with the public housing association Plaine Commune Habitat. The aim is to appeal to a heterogeneous group of residents – both people on low incomes and young families who want to build up property through the BRS model.

With a construction cost of around seven million euros and a living space of 2,775 square meters (SHAB), the project is within the scope of what is feasible in a subsidized context. The “NF Habitat” certification and compliance with the French thermal insulation regulation RT 2012 with a 20 percent reduction underline the ecological focus.

Those involved in the project include Bollinger+Grohmann (structural engineering), ENEOR (building services), Le Sommer (certification) and Topager for the landscape architecture. Cap-Exe was responsible for coordinating the various trades.

What can be deduced from the project in Saint-Denis for the current housing debate? Certainly not a new type. Rather, it shows how a combination of solid planning, serial production and municipal control can make a contribution to sustainable urban development – beyond creative exaggeration, but also without falling into banal functionality.

The architecture remains restrained but deliberate. It unfolds its effect through everyday use – as a place to live, to meet and to reappropriate a long-neglected urban space.

31.10.2024

Ukraine war: Мы за мир

Building design

As a result of the war in Ukraine, the European architecture scene has quickly taken a public stand against the Russian war of aggression. G+L also stands in solidarity with the Ukrainian people and government.

BIG, David Chipperfield Architects, Foster + Partners, gmp, Herzog und de Meuron, MVRDV, OMA, Snøhetta, Zaha Hadid Architects – as a result of the war in Ukraine, which violates international law, the who’s who of the European architecture scene publicly opposed the Russian war of aggression in a very short space of time at the end of February/beginning of March 2022. Within just a few days, numerous offices expressed their solidarity with the people in Ukraine and with all those who stand for peaceful coexistence – above all via social media. In the case of Chipperfield, HdM, OMA and Zaha Hadid, the public statements were followed by an immediate halt to all construction projects in Russia. BIG also announced in a statement that the office would not be carrying out any projects in Russia or for the Russian government. However, it is not clear from this whether a construction freeze has been imposed or whether there are simply no Russian projects currently in progress.

First the governments, then the private sector. Today, our globalized world also makes it possible for corporations, companies or even planning offices to impose sanctions. So while Apple, Siemens, Starbucks, McDonalds, Coca-Cola, Pepsi and the management consultancies KPMG, PWC, EY and Deloitte are suspending their business in Russia as a result of the war of aggression, or Elon Musk is actively supporting Ukraine with the help of his satellite internet service Starlink, including reception systems, the world of architecture is also drawing its own conclusions. This is worth a special look, as it was or is precisely non-democratic regimes such as Russia or China that have provided the big star offices with unique construction projects in recent years. The M+ Hong Kong designed by HdM only opened at the end of 2021. While at the turn of the year in Moscow, the Renzo Piano Building Workshop RPBW converted the GES-2 power station into a center for visual and performing arts for the V-A-C Art Foundation.

Jacques Herzog on democratic architecture

For us in the editorial team, this immediately (and once again) triggers the question of how political planning can be, but also how political planning must be. What is exciting in this context is that Jacques Herzog in particular has repeatedly publicly addressed the question of democratic architecture. You can think what you like of him and the HdM projects, but he takes a stand. As he did in an interview in 2020 with Lukas Gruntz from architekturbasel.ch. Referring to the historic urban development of St. Petersburg, Venice, Rome and Paris, he said here: “Perhaps more beauty is created in a non-democratic context because the context is more extreme, more radical.” But he also continued: “From our point of view, an enlightened and democratic society, architecture must be anchored in the population and ideally emerge from the needs of the population.” Sentences that should make us think. Now more than ever.

Ukraine war: Coop Himmelb(l)au under pressure over Crimea project

Lighthouse projects in non-democratic regimes must be better considered in future. I wonder what is going through Wolf D. Prix’s head at Coop Himmelb(l)au right now? His office was criticized even before the war of aggression. Since 2020, the Viennese have been planning two of the four cultural buildings that Vladimir Putin wants to be built by 2023. The particularly tricky case is the planned opera house on the Crimean peninsula, which was annexed by Russian occupiers in 2014 in violation of international law(more on this in an SZ-Plus article). With reference to the lighthouse project, Ukrainian President Volodymyr Zelensky imposed economic sanctions against the Viennese architecture firm and six of its representatives on January 21, 2022.

Wolf D. Prix: Coop Himmelb(l)au is building an opera house, not barracks

According to an SZ.de article by Gerhard Matzig, who interviewed Prix on the subject, this was preceded a year and a half ago by threats from the Ukrainian embassy to Coop Himmelb(l)au. Prix would not be allowed to build the opera house in Sevastopol or the architectural firm would soon be ruined. And according to Gerhard Matzig in his article, Prix has now also been advised to distance himself from the project and Putin. When asked by Matzig whether he would do so, Wolf D. Prix sighed on the phone. Prix is of the opinion that he is not building a barracks, but an opera house. As a cultural project, this is not subject to the embargo regulations. Unsurprisingly, as of mid-March 2022, Coop Himmelb(l)au still has no statement on the Ukraine war.

Ukraine war: Russian planners make their mark

But now back to those who openly oppose the war. Because it’s not just the European star offices that are flying the flag. According to SZ.de, a total of 6,500 Russian architects, designers and urban planners also signed an open letter on the website of the Russian architecture magazine “Project Russia” between February 26 and March 4, 2022, calling for an immediate end to the war. The tragedy is that this appeal also fell victim to the “fake news” law against critical reporting on the Russian army signed by Vladimir Putin on March 4, 2022. Only a short version of the campaign with a picture of a dove of peace can now be seen on the site. It says here in Russian: “Unfortunately, we were forced to remove the text of the letter under threat of criminal liability under the law that came into force today. We are for peace!”

One profession, one passion

Meanwhile, however, the Union of Architects of Ukraine also called on the International Union of Architects to expel the Union of Architects of Russia from the organization. “Those who do not condemn Russia’s actions support them,” the Süddeutsche Zeitung quotes the President of the National Union of Architects of Ukraine, Oleksandr Chyzhevsky, as saying in a letter to the UIA. If you let this statement sink in, you have to ask yourself – even if you condemn Russia’s actions in the strongest possible terms – whether we really want to live in a world in which people from one industry, one profession, one passion, go against each other simply because of their nationality. For this very reason, the G+L editorial team would like to join our Russian colleagues: Мы за мир. We are for peace. And we condemn the Russian government’s attack on Ukraine, which violates international law, and stand in solidarity with the Ukrainian people and government.

Ukraine war: bdla and BAK also active

While German landscape architecture firms are still quite reluctant to express their solidarity, the bdla published an official solidarity statement #StandWithUkraine on March 2, 2022. The bdla declared its “deepest regret about the war in Ukraine, the loss of human lives.” It condemns this attack, which violates international law. The bdla’s thoughts are particularly with its colleagues from its partner association, the Guild of Landscape Architects of Ukraine. In the same letter, the bdla refers to the initiative of the Federal Chamber of Architects. This has set itself the goal of becoming active beyond expressions of solidarity. For this reason, the BAK is making its network available to the Ukrainian Association of Architects. The goal: sleeping places for refugees. Find out more here.