Green roofs help houses fight the urban heat island effect

Text: Qiu Jianxian / Wutong Environmental Integration Foundation
Image source: Wutong Environmental Integration Foundation

When the weather turns hot, people put on an extra hat when they go out to block the sun and keep out the heat, and adding a green hat to a roof has a similar effect. The so-called "green roof" means planting vegetation on the roof of a building; besides providing insulation and cooling, it also offers functions such as urban beautification, air purification, reduced carbon emissions, and rainwater retention. At the green roof seminar "Reducing the Urban Heat Island Effect: Everyone Make a Green Roof," hosted by the Taipei City Building Management and Engineering Office, experts and scholars were invited to share knowledge and case studies on green roofs, and more than 700 people packed the venue, showing that the public cares a great deal about this issue.
The Taipei City Government has already stipulated clearly that starting in 2014, building projects worth more than 50 million need to have green roofs covering more than 50% of their area. At the same time, 2 elementary schools will also be selected in the future for rooftop greening demonstrations. We welcome the implementation of green policy, and of course, in the future, besides playing a supervisory role, the public would do best to also take part in the urban greening movement.
Many residents grow vegetables and flowers on their balconies and roofs, and these are all part of rooftop greening; besides letting them provide for their own enjoyment, this can also improve environmental quality. Roofs used for growing vegetables mostly belong to the "container-style" green roof form, planting vegetation in container molds; it is not only simple and easy to start with, but can also achieve rapid greening results, and even though it requires more time for maintenance and management, it is strongly endorsed by experts. Roofs used for growing flowers and trees belong to the "garden-style" green roof, with high ornamental value, but they require a certain level of skill in construction and subsequent maintenance and management. For example, to plant small trees, the soil thickness needs to reach 80-90 cm to effectively provide for plant growth; shrubs need 40-60 cm, and herbaceous plants 15-30 cm, and the above will all be adjusted depending on the species.
The organic matter in the soil must also be taken into account, as it decomposes the soil layer and lowers its thickness. In the past in California, USA, there was a case where too much soil organic matter caused the soil layer to drop by 40 cm within 15 years. The third form of green roof is the "thin-layer-style," which mainly involves planting ground cover plants; it can be planted over large areas, has ecological functions, and can achieve an environmentally harmonious effect. Although the thin-layer style does not require long-term maintenance and management, the precondition is that the plants must be drought-tolerant and dry-tolerant, so there are fewer varieties to choose from.
Whichever form of green roof it is, we must create a good living environment for the plants, and the quality of drainage and water retention is a major indicator affecting the quality of the environment; this is also a common difficulty encountered in building green roofs. We want to retain water resources, but we also do not want a heavy rain to turn the roof into a pond. Although there are now many products to solve the problems of drainage and water retention, scholars still believe that research in this area is necessary.

Besides putting on a green hat to improve the environment, can we also put on green clothing? Of course we can! Wall greening is more challenging than roof greening; the fixing of the medium, the method of vascular support, and how to retain water all need to be tested. Wall greening can achieve a more beautifying effect than putting a green hat on a roof, and the wall greening at National Taipei University of Technology is a very good example. A German expert pointed out that when the area of roof and wall greening reaches 70%, urban temperatures can be expected to drop by about 5 degrees. Besides roofs and walls, bus stop signs, billboards, and even vehicle roofs are all spaces where greening can be applied.
Among the cases shared at the seminar, the roof of the Xinyi District Office was greened with succulents, lowering the summer temperature by at least 3-5 degrees. In addition to its roof, the Renyi Building in Shunde Village also had its walls greened, and the once-a-year weeding was all the maintenance and management they needed to do. At the same time, the enthusiastic neighborhood warden Li Hongzhi also led community residents to join the urban greening trend.
After hearing so much about the benefits of rooftop greening and the successful cases, do you also want to try it yourself? Imagine your own roof as an organic vegetable garden, imagine butterflies and birds flitting and dancing through the urban jungle, imagine your own community like the Hanging Gardens of Babylon!!! Stop imagining! Hurry up and help your own building put on a green hat and build a green roof of your own!