Green building envelopes for lower city temperatures
It’s never been more important to design buildings to offset the urban heat island effect created by our cities.
The ongoing march to greater urbanization challenges designers to create interventions that ensure cities remain liveable. The positive and balancing role played by trees, plants, and green space in cities is well-understood, but building design could play a more active part in terms of acoustic performance, air pollution, and the Urban Heat Island (UHI) effect. I believe that by greening the external "envelopes" of a city's buildings, there is a great opportunity to offset the UHI effect that's driving up urban temperatures.
This effect is a result of cities' combination of heat-retaining structures, dense population, waste heat from building operations, and other human factors. These raised temperatures, in turn, encourage their populations to use more energy to artificially lower the temperature or improve ventilation in their area-outcomes that are neither desirable nor sustainable.
Green building envelopes could offset these unwanted gains. The building envelope refers to its roof, façade, and any other areas that connect the inside to the outside, usually representing 20% to 25% of a building's total external area. Even in the height of summer, interventions like vegetated roofs can help bring down the temperature to ambient levels, whereas a conventional roof can be up to 50°C higher.
Green envelopes can be retroactively applied to buildings' exteriors, too, making them an economically viable adaptation that can transform the urban built environment's long-term performance. The opportunities take many forms, from living walls that shield sunlight and noise as they lower the temperature, to roof gardens that replace lost urban squares.
Managing an effect as complex and dynamic as urban climate requires a context-sensitive approach and rigorous planning. Research needs to focus at both the citywide and neighborhood scales. Research conducted in 2007 showed that if Greater Manchester increased its green infrastructure by 10% (in areas with limited or no green cover) the city would reduce its average temperature by up to 2.5°C, greatly offsetting the UHI effect.
Some densely developed cities like Singapore are already leading the way. Their Sustainable Growth Strategy has set a target of 0.8ha of green space per 1,000 persons, aiming to increase greenery in high-rise buildings to 50ha by 2030. Reducing the UHI effect is the goal, closely followed by improvements to air quality, noise reduction, stormwater attenuation, and increased urban biodiversity.
Any kind of city can benefit from this commitment to finding green potential from within its structures and layout, from the wide lanes of a city like Los Angeles to the narrow streets and squares of an ancient Asian capital. By rethinking and greening the exteriors of our buildings, we can build cities that are more resilient, enjoyable, and suitable for their growing populations.
This is an important and evolving topic, particularly given the effects of climate change. I'd be interested to hear about any great examples of green building envelope design you might have encountered in the comments below.
-Rudi Scheuermann is an Arup Fellow leading the company's global Building Envelope Design practice. This article originally appeared on Arup Thoughts. Arup is a CFE Media content partner. Edited by Joy Chang, Digital Project Manager, CFE Media, firstname.lastname@example.org.