Urban Heat Phenomenon and Green Roofing

Roof Gardens From Hong Kong to Brazil

What are the real benefits of roof gardens and are they providing feasible solutions to heat islands and food desserts?

Well, it might depend on where you are and who you are asking. The benefits of cultivating green landscapes atop urban architecture are numerous. Flood prevention, decreased noise pollution and increased biodiversity are a few happy byproducts; as are the marvelous abilities of greenery to cool an area, increase air quality and, depending on the plant, provide a local food source. 

As simple as adding plants to a roof sounds, it actually involves much more policy and infrastructure consideration then we tend to pause and consider. Problems the favelas of Brazil are looking to solve, might be altogether different than issues facing the residents of downtown Toronto or Hong Kong and require different metrics for determining success.  Fortunately for many residents living in heat islands and food deserts, green roofing innovation is providing real solutions to concrete jungle problems.

Brazil

In Brazil, where green roofing hasn’t been feasible in the lowest income areas where it is needed most, a polyester geotextile made from recycled plastics is making it possible for families to take advantage of roof gardens as a cooling system. Bidim, the geotextile, is lightweight enough that even homes and buildings constructed without architectural codes in mind, can benefit from the cooling effect of plants without risking complications from excess weight of soil and steel beaming utilized by pricier roof landscaping technologies. It also offers a low-maintenance, and therefore low-cost, option for Brazilian families looking for a way to cool down their homes during the long hot summer months; as much as $10 cheaper compared to traditional asphalt blankets.

A 2015 study in Brazil showed a 36 degree difference between heavily populated areas of Brazil where there was little to no surface area available for landscaping versus nearby vegetated areas of land. Compared to paying for the electricity to run fans and air conditioning units, growing greenery that absorbs and reflects the hot sunlight seems like a realistic way to bring temperatures down. Yet, urban residents have been slow to adopt the option claiming the process of cultivating a green roof and learning how to properly care for plants is much more time consuming than simply plugging in a fan.  

Urban environmentalists fear that if summer months become hotter or last longer energy demands will become too great and heat islands will face more serious problems. If they can reduce pressure on energy sources simply by planting more greenery they believe it can have a positive effect on city living for the next generation.

Canada

In Canada, green roofing is fast becoming a normal part of urban living. From Toronto to Vancouver cities are incorporating both greenery as a cooling system and in some instances, food co-ops for local residents.  Urban garden designs are now a mandatory consideration for engineering projects. In fact, in Toronto any building with 2,000 square meters of roof space must be built to accommodate green roofing of some type. Over 1.14 million acres of green roofing projects have already been completed which the city says has contributed to a decrease in energy usage by owners, diverted rainwater and helped to mitigate the impacts of heat waves.

The cost of installing green roofing systems in Canada has been expensive, and not without obstacles. Complex designs that not only cool a building, but add accessibility for residents to connect with nature certainly cost a lot of money, but they also weigh a lot. Water trapping systems add pressure to building structures and they can create problems with mold and fungus if water isn’t held properly. Despite these major issues other Canadian cities are adopting green roofing as a tool for temperature cooling, air pollution and flood prevention and developing fiscal policy to offset investments made by residents.

China

Hong Kong and other cities in China have faced similar obstacles when it comes to green roofing. Architectural designs and socioeconomic disparities have been linked to a slow adoption of green roofing as a feasible tool to combat rising temperatures in urban areas. Like Canada, new construction often incorporates green roofing designs from the get-go to ensure that live plants and water collection don’t jeopardize structural integrity. But, asking current top floor residents to approve the garden additions has proved difficult. 

The green roofing industry boomed in Germany and Japan in the early 2000s and with it came a surge in green roofing companies. Major cities in China, and all over the world, jumped on the green roof bandwagon and began to build gardens on top of homes, apartment buildings and office skyscrapers. The rush to greenify led to major leakage issues in Hong Kong and other cities. Residents have had a bad taste in their mouth for green roofing methods. Like Brazil, perhaps geotextiles will prove to be a better option for urban areas in China as well.

Green Roofing Competition

Also contributing to the pace of growth for green roofing is solar energy. Convenience is a huge driver of feasibility when it comes to adopting environmentally friendly solutions to the urban heat phenomenon. As much as city dwellers might enjoy the idea of more greenery and its potential for lowering temperatures in concrete heavy areas, it is much easier to turn up the air conditioner or plug in a fan. More and more buildings are opting to use solar panels as a means of trapping sunlight and converting it to energy.  Solar energy has become competition for green roofing. And, many countries incentivize the installation of solar panels more than green roofing.

The future of urban dwelling is sure to incorporate both strategies in the hope of maximizing all the benefits. Future aerial views of cities like Chicago, Toronto, Rio De Janeiro, and Hong Kong will likely show rooftops sporting both plants and solar panels as residents look for ways to reduce electric bills, stay cool and bring greenery back to urban areas.