Thermal Governance, balancing sun and shade

Cities are experiencing rising temperatures, creating challenges for architecture. How can we effectively manage temperature throughout the various seasons? Professor Sascha Roesler and PhD assistant Julian Raffetseder from the USI Academy of Architecture discussed this topic in an article written in collaboration with laRegione.

At night, buildings release the heat they have absorbed during the day, causing temperatures in cities to rise higher than those in surrounding rural areas. As a result, global warming presents new challenges for urban areas. Cities must not only address the issue of heat islands but also reconsider the relationship between their buildings and the quality of public spaces. While many believe that increasing the number of trees and urban greenery is enough to combat heat islands, experts suggest that a more comprehensive and interdisciplinary approach is necessary. This includes employing innovative building materials alongside the presence of greenery.

To address this emergency, the Academy of Architecture at Università della Svizzera italiana has presented the innovative Thermal Governance project. This approach focuses on the distribution of sun and shade in urban environments. The model developed, therefore, concentrates on achieving a difficult and often precarious balance: ensuring the presence of sun in the colder months and generating protective shade during our increasingly hot summers.

Curated by Professor Sascha Roesler and PhD assistant Julian Raffetseder, the project was chosen to be part of the Swiss Pavilion Exhibition at the Osaka World Expo, which opened on 13 April and closed on 13 October, elevating USI's research onto a prestigious international stage. We asked them a few questions to understand better what this is all about and what its implications are.

Based on current data, cities are becoming increasingly hotter. Is it still possible to intervene and reduce temperatures, or must we now focus solely on preventing further rises?

"The main objective must be to reduce CO₂ emissions. If we fail to do this, urban heat will continue to rise. Additionally, we must adapt our cities to ensure they remain livable during heat events. While heat prevention measures are important, it is crucial that we focus on reducing emissions to stabilise the climate in the long term."

In general, what interventions are needed in urban spaces?

"Urban spaces must be valued for their microclimatic diversity. While they can function as "heat islands" during the night, they also offer "cool islands" during the day in places like courtyards, parks, arcades, and interior spaces. It is essential to identify, preserve, and enhance these areas. This involves unsealing the soil to promote water infiltration, providing shade, and allowing for proper ventilation."

In practical terms, how can an architect take action?

"These qualities must be considered important design factors, in addition to the purely visual aspect. Architects and urban planners must understand that the shape of buildings affects soil sealing, ventilation and shade distribution. With climate change, we cannot rely on habitual experience: we must actively anticipate future climatic conditions."

Is it a question of the shape of buildings, the materials used, or both?

"There is no one-size-fits-all solution. Both the design and materials used impact the microclimate. Additionally, this issue is not solely technical; it also has social implications. Our objective should not be to cool entire cities, but rather to create comfortable thermal conditions in the spaces where people actually spend their time and need them."

You recently presented the concept of Thermal Governance at the Osaka Expo. What is the idea behind this project?

"Thermal Governance emphasises that urban climate adaptation is fundamentally a political endeavour. In shared urban spaces, various interests and priorities converge, necessitating public discourse. The project presented, which is part of Julian Raffetseder's doctoral research, examines this concept in relation to the distribution of sun and shade in a future "subtropical Vienna." On hot days, shade plays a crucial role in human thermal comfort, and buildings are the primary sources of shade. The project aims to strike a balance between ensuring access to sunlight throughout the year and meeting the need for shade during the summer months. After all, cities consist of buildings, which provide shade at no cost."

How can sunlight and shade be modulated in urban environments, which are often already developed?

"Cities are continually evolving and experiencing a rising demand for new housing, often facing pushback from residents. One approach to address these challenges is the concept of Thermal Governance, which provides a framework for implementing targeted shading strategies. This concept helps identify areas where taller buildings may be beneficial and where open spaces should be maintained. It fosters public discussion about the balance of sunlight and shade in our urban environments and how to achieve it. Potential measures include temporary sun sails, tree planting, and thoughtfully designed building extensions."

Could you give some examples?

"Many European cities aim to increase trees to provide shade. Sometimes streets are covered with sun sails during the summer. The narrow streets and arcades of southern cities offer natural shade. The Osaka project proposes a similar approach: instead of uniformly narrowing the roads, strategic moments of shade are created, producing a more heterogeneous urban landscape."

How has the project been received?

"Cities are becoming more aware of the importance of summer shade, but they often struggle to find effective ways to provide it. While trees are the preferred option for shade, they cannot be planted everywhere and often face challenges such as heat stress, water scarcity, and excessive sun exposure. Urban representatives have recognised the need to re-evaluate the shade created by buildings, highlighting the importance of balance and thoughtful design choices. This is precisely what the project aims to test and implement.

Honestly, do you think it can have a practical application, or will it remain a mere theory?

"The shape and height of buildings are important concerns for urban residents. This project aims to promote public discussion about the role of sunlight and shade in urban environments and how cities should manage their distribution. We can learn valuable lessons from southern cities that feature narrow streets and cool courtyards. It is essential to reclaim this historical knowledge to design cities that will be well-suited to future climate conditions."

Content edited and published in collaboration with laRegione.