Cities can be seen as ecosystems. Just as individual organisms contribute to sustaining an ecosystem, individual buildings support the overall functioning of the city. In contrast with a smart system, current approaches to building design define buildings as single entities within an urban fabric, dependent on external resources and shielded from external impacts. Potentially the envelopes of inner city buildings can more actively contribute to improve the city environment. Building envelopes can be utilized to mitigate air pollution, acoustic noise or urban heat island effects. Multifunctional vegetation systems can contribute to significantly improve environmental conditions. With improved quantification of the advantages of green building envelopes – by making the benefits measurable – more opportunities to make use of natural ventilation, free cooling and healthier conditions can be created to the benefit of urban populations.
This Arup research study provides insights into the impact of green building envelopes on our urban environment. An interdisciplinary team of Arup specialists quantified the potential to mitigate urban noise, air pollution and urban heat. Up-scaling from individual buildings to the city level, five major cities with very different climates and city scapes – Berlin, Hong Kong, Melbourne, London and Los Angeles – were selected and evaluated.
Green envelopes contribute significantly to the sustainable performance of dense urban agglomerations and more importantly to the general well-being of the city population.
For air pollution, the study demonstrates that green facades can result in local reductions in concentrations of particulate matter typically 10% to 20%. The reduction is highly dependent on the configuration of the buildings and streets in terms of the ratio of the height of the buildings and widths of the streets.
For acoustic noise, green envelopes could reduce sound levels from emergent and traffic noise sources by up to 10 dB (A). They do not significantly improve noise level reduction close to a noise source, but show greater improvements with increasing distance from the source up to the point where ambient noise begins to dominate.
For urban heat, green facades are most effective in reducing urban heat islands in cities with a height to width (H/W) ratio greater than 2: very dense urban city centres such as Hong Kong and Melbourne fall into this category, peak temperature reductions of up to 10°C have been modelled.
A summary of this research is presented in the Arup publication Cities Alive - Green Building Envelope, which is available online at www.arup.com.
The methodologies developed in this study enable Arup to quantify the benefits of green building envelopes. This can help our clients take better informed decisions based on quantified cost-benefit analyses. Our approach uses the quantifiability of acoustic noise, air pollution and urban heat effects at the building scale, as well as their cumulative impacts at the district scale. This approach enables Arup to provide more holistic and integrated urban designs that enhances the well-being of city dwellers and the liveability of cities.
Building envelope surfaces should to be considered as an essential resource that can make a significant contribution to benefitting their external environment. This requires a move away from more traditional and inwardly focused performance considerations for buildings, instead looking at how building envelope surfaces can perform to create healthier environments, better social conditions for people, and resilience to the effects of climate change.
For existing buildings and future developments, developers, planners, practitioners and designers of the built environment in all disciplines need to take on the challenge and responsibility of creating more positive and healthier approaches to building design. Green building envelopes can contribute significantly to this, and become a default design approach for building design. This will require a significant rethink of current design considerations, by making health and well-being a starting point for urban building design.