By Jakob Strømann-Andersen, Partner & Head of Sustainability, Henning Larsen Architects
I am often asked how we work with sustainable challenges in Henning Larsen. For me, the question is rather how we turn the challenges into opportunities. How can sustainability drive the design instead subtracting from the design? And not least – what tools can we use to create great architecture that is of value for people and society?
I think these questions are very relevant on many scales. Our cities are growing. Globally, across Scandinavia, in Norway – the larger cities are expanding and getting denser with buildings ever more complex. As architects and urban planners, we need to take responsibility for the health and well-being in our cities in this process.
By being part of Building Green Oslo, we have the chance to present and discuss tangible sustainable methods and solutions that combine a human and holistic approach with hardcore knowledge. I will kick start this dialogue here, by addressing some of the tools and methods we use on a daily basis.
A tool completely necessary for designers when it comes to improving the air quality in cities is Strategic Microclimate Analysis. Urban microclimatic is a local set of atmospheric conditions (wind, sun, humidity etc.) that has significant influence on the concentration of air pollutants in cities. Therefore, to actively reduce poor air quality in cities, we need to understand and simulate the urban climate before we design our urban space.
As promised – here are three steps to designing for better air quality:
- Let urban ventilation do the work
Wind flows, temperature gradient, solar radiation and humidity levels influence pollutant concentrations and dispersion. The urban wind flow determines the level of urban ventilation, which transport pollutants by advection and mixes it up with cleaner air by turbulence. In general, low wind speeds creates a more favorable environment for the chemical reactions necessary to create ozone and particle pollutions (EPA, 2007). Therefore, it is necessary to create ventilated corridors where the city can “breathe”.
- Use trees, and use them right
If trees are not blocking the wind, they are a great help in reducing air pollution. Trees absorbs the greenhouse gas carbon dioxide and leafs beneficially captures, and contains, nitrogen dioxide. Not all plant species are as effective, however. Finer, more complex structured foliage is most effective in capturing particulates. Conifers are effective because of their fine structure of hairy needles, but also because they are evergreen and therefore retain their function in the winter. Common ivy – also an evergreen plant – is also good at capturing particulates, especially the finer fraction PM2.5 (Ottelé et al., 2010). Knowing the collection of dominant pollution types for the specific location is valuable for informing the vegetation strategy.
- Consider building heights
The difference in building height also influence the mixing of pollutants with clean air. Studies addressing pollutant dispersion in relation to urban geometry shows that urban ventilation is depending on how the urban street grid is orientated to the prevailing wind directions. As a rule of thumb, urban ventilation is beneficial if there are pollutants emitted inside the street canyon, for instance from traffic. In cases of no pollution sources inside the canyon, it can be favorable to shelter from the background-polluted winds.
This is just one example of how we work to use knowledge combined with architecture, so sustainability becomes an actual design driver. I look forward to diving into more solutions at Building Green in Oslo!