In order to ensure greater sustainability in urban development, the built environment is an important factor. This term encompasses the entirety of man-made infrastructure; that is buildings, transportation networks, and public facilities. The built environment was responsible for over half of all greenhouse gas emissions in 2010. But other emissions are also produced in cities, such as air pollution and noise.
Buildings interact with the environment
In order to be able to develop strategies for better sustainability, the exact emissions in cities first need to be determined. Studies conducted to date often focus on individual buildings whose emissions were calculated from factors such as energy and water consumption, as well as materials, transportation, and design/construction. Other studies are conducted at the city level, where among other things the effects of traffic and population density on the environment are investigated.
The problem with these approaches is that “buildings interact closely with their environment,” explains Dr. John Anderson, who wrote his doctoral thesis on this topic at the TUM Institute of Energy Efficient and Sustainable Design and Building. So far, there have not been any studies that take into account the interaction between the building and city levels.
Determining induced effects
When buildings are examined as isolated objects, the inhabitants of an apartment building in the country would generate exactly the same amount of emissions as in a major city. But this is not the case. On the other hand, focusing only on the city level is also problematic, as major changes such as the growth of a city take place at the building level.
A new calculation model, which Anderson developed in collaboration with Prof. Werner Lang (Institute of Energy Efficient and Sustainable Design and Building) and Prof. Gebhard Wulfhorst (Chair of Urban Structure and Transport Planning), now allows the multifaceted and complex mutual interactions between the building and city levels to be determined — the induced impacts.
Apartment dwellings in the city more energy-effective than single-family dwellings in the country
The researchers use a case study to demonstrate how these induced emissions can be calculated. They examined three building types: an apartment building, a terraced house, and a single-family detached home. Furthermore, they also analyzed the traffic infrastructure at three locations: the city center, the suburbs, and rural areas.
The scientists included the following four categories in their calculations:
- The building itself: raw materials, transportation, manufacturing, refurbishment, and ultimately demolition and disposal
- Use of the building: energy and water consumption, air conditioning and electricity
- Vehicles and traffic routes: includes materials, manufacturing, disposal, and repairs
- Use of traffic infrastructure: no. of kilometers which are traveled with a particular means of transportation
Subsequently, they correlated the building level with the city level — represented here by the traffic infrastructure. The apartment building in the city center, the terraced house in the suburbs, and the single-family detached home in the rural area. The calculations also include factors such as the percentage of people at the respective locations who own a car, or the fact that the subway only runs in the city center and in the suburbs.
According to the calculations, the study showed that the apartment building in the city center generated the lowest emissions, followed by the terraced house in the suburbs, and finally the single-family detached home in the rural area. As expected, travel habits had the greatest influence: In the city, inhabitants used public mass transit more often, while the people in the rural areas depended on the use of cars. The energy consumption of an apartment building, the most common form of residence in the city, is also lower. For one, less heating is required, as the apartments are all adjacent to each other, and heat is transferred via the walls and ceilings.
The findings also show that different strategies need to be used at the various locations in order to increase sustainability, explains Anderson. For example, the greatest potential for reducing CO2 emissions in the city center could be found in transportation habits. Hence, the conditions for pedestrians and cyclists should be improved. In rural areas, the greatest savings could be achieved through the energy consumption of the buildings. In the suburbs, both measures are effective.
The new methodology has been included in the new European Commission Science and Policy Report “Identifying macro-objectives for the life cycle environmental performance and resource efficiency of EU buildings” and thus has been recommended at the EU level.