A Truly “Green” Building Technology
From ‘green movement,’ ‘Green Party,’ ‘green collar jobs,’ to ‘Greenpeace,’ the color reference is to plants, chlorophyll, the green pigment central to photosynthesis, which is the basis of all life. Quite often, however, the chief environmental goal being advocated has little to do with plants, but rather promoting low-impact technologies, practices and lifestyles.
This is the case with “green building design” which is receiving growing attention because of the under-appreciated magnitude of building emissions worldwide. Recently, New York City audited the source of all its CO2 emissions and found that nearly 80 percent is from building energy consumption. Worldwide the estimate is closer to 45 percent, making “buildings the biggest single contributor to anthropogenic climate change – a worse offender than all the world’s cars and trucks put together.”
The vast bulk of green building design focuses on efficient heating, cooling, lighting, insulation and window technologies. All of these are great things of course, but what’s not mentioned in the Nature article is a truly ‘green’ building technology – living green roofs and living walls. These are technologies that introduce plants into building facades, especially rooftops.
Typical dark rooftop temperatures in summer sunlight can reach extraordinary levels of 150 degrees F (~65 degrees C) or more. It makes little sense not to address such an extreme building heat source in green building design. Moreover, in cities, rooftops, among other dark, impervious surfaces like streets and parking areas are a chief contributor to the “urban heat island” effect which elevates the temperature and climate in cities well above surrounding suburban and rural areas. This extra heat can be deadly during heatwaves, especially if air-conditioning is not available or fails during blackouts. Resident proximity to high-floors and rooftops was a risk factor in both the deadly 1995 Chicago and 2003 European heat waves.
Green roofs harness the unrivaled power of plants to remain cool when exposed to sunlight during the summer, as I showed in my last post. There is an ever-increasing palette of plant choices available, but the most common and reliable are “sedums.” They are members of the succulent family of plants and are very tough in surviving all sorts of weather conditions, including extreme heat and droughts. The plants grow in a porous medium that is usually a few inches deep, depending on the building structural support.
Green roofs give back to the urban environment in multiple ways however. Along with urban heat source reduction they are great at reducing storm-water runoff from buildings as well. This runoff leads to a ubiquitous problem in cities known as “combined sewer overflow” where combined sanitary and runoff water is released to nearby waterways because of limited water treatment capacity. Green roofs can also create new ecological habitats that are generally limited in urban areas. It’s estimated that New York City may have 10 or more times the area of Central Park available for green roof adoption.
Green living walls, including ivies and vines, are a more challenging technology and will take longer to develop into a common building practice. But already fascinating potential properties of living walls are being noted, such as how in summer they can provide shade to cool buildings down, while in the winter they will allow light to penetrate and warm the building.
If these green building facade technologies catch on, along with traditional street trees, plants will partially re-conquer the urban spaces they originally occupied, and make cities much more liveable for us in the process.