Planting vegetation on buildings can bring many perks for those that can afford them, but the environmental benefits should not be overstated.
The apartment block where Anne Kimemia lives, in the upmarket Nairobi suburb of Kileleshwa, boasts many luxuries such as a private gym and swimming pool. But arguably its greatest perk is its least obvious.
The very top of the building, in Kenya's bustling capital, is covered in vegetation. This seemingly simple innovation is not just an aesthetically pleasing design feature but brings a wide range of benefits - not least to residents' pockets.
Kimemia, who lives in one three-bedroom apartment and rents out another, says her monthly water bills are less than half what they would be in a conventional block. She adds that she barely needs to use air conditioning when it's hot or a heater when it's cold.
"These green features help a lot," she says. "The roof does all the necessary work."
Several studies show that "green roofs" can have many advantages. Covering the tops of buildings with vegetation can add thermal insulation as well as shield buildings from intense heat, reducing energy demand for air conditioning by up to 75% in the summer. Green roofs absorb rainwater, decreasing water usage and the risk of urban flooding. And they can provide a habitat for birds and insects, supporting biodiversity in cities.
As the climate crisis leads to more extreme weather patterns and efforts to reduce emissions, green roofs have become increasingly popular. The global green roof market is valued at $2.1 billion and predicted to more than triple by 2032. The Intergovernmental Panel on Climate Change (IPCC) cites green roofs as an important part of building resilience as heatwaves increase in intensity and frequency and as a way to reduce urban greenhouse gas emissions.
In Africa, Nairobi is a leading adopter of green roofs along with other major cities such as Durban, Cape Town, Johannesburg, Lagos, and Cairo. The Architectural Association of Kenya (AAK), the umbrella organisation that regulates architects in the country, estimates that there are so far nearly 200 buildings - mostly apartments, offices, and hotels - with green roofs in Kenya. It says that about 30 more are under construction in East Africa, mostly in Nairobi, and that several more are in the process of being approved. It estimates that construction of green roofs in the region is growing by about 12% per year.
"Green roofs are a must-have," says Mithika Mwenda, founder of the Pan African Climate Justice Alliance (PACJA). "With increasing frequency and intensity of extreme weather events such as the recent floods in Kenya due to climate change, they are vital for cities to adapt and build resilience."
Costs and challenges
Green roofs, however, are not without their challenges. To begin with, they can be costly and complicated to install. Construction requires several stages from waterproofing to adding a root barrier, drainage layer, filter layer, and growing medium before planting vegetation. Some projects add irrigation systems and solar panels. When green roofs are added to existing properties, they also typically require structural reinforcement given the weight of the roofs. Once built, the roofs require ongoing maintenance, both to tend to the plants and to prevent leaks and fire hazards.
"It costs me lots of money for maintenance and eventually repairing or replacing the roof every few years," says John Mwaura, a landlord and real estate investor. "I have to pass on the costs by increasing the rents of my tenants."
One effect of these costs is that green roofs are only available to the very wealthy. A three-bedroom apartment in Kimemia's block costs nearly $200,000. Kenya's average annual income is about $7,500.
Lax regulation and the temptation to cut corners in construction can make matters worse. Florence Nyole, President of the AAK, says that despite the industry's steady growth, there are very few qualified professionals specialising in green buildings in Kenya. As a result, she says that "many of the builders [that work on green roofs in Nairobi] are not regulated and professional."
To tackle this problem, Kenya's Ministry of Lands, Public Works, Housing, and Urban Development says it has directed professional bodies to come up with effective green building codes. This will mean more stringent regulations, but David Chola, an architect in Kenya, emphasises that they will only make a difference if the government ensures that builders comply with them.
"We have good laws here in Kenya, but many are not enforced," he says. "Corruption and laxity remain a challenge. If directives are not adhered to, many property owners and developers build how they feel."
The Ministry says it hopes to make green roofs more affordable by encouraging more construction, including by recently making it mandatory for green roofs to be installed in buildings located in certain parts of the capital.
"We want to invite more companies that specialise in green construction," Charles Hinga, Principal Secretary in the Ministry, told African Arguments. "We have the opinion that this will lead to widespread availability of the roofs. With the availability of the products and demand being met, we believe the prices will go down - together with added economic tax incentives."
A piece of the green puzzle
Climate experts, architects, and urban planners agree that green roofs can be effective in reducing energy usage and building resilience to extreme weather. But, as well as their challenges, they also stress their limitations. Their capacity to support biodiversity, for instance, remains unproven. Urban planners have warned that roof-top vegetation should not be treated as a replacement for ground-level habitats.
"There are structural limitations, and you can only plant a limited number of trees and other vegetation such as grass," explains Nasra Nanda, CEO of the Kenya Green Building Society.
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Green roofs can also, at best, cover a relatively small amount of surface space. Nairobi is one of the fastest growing cities in Africa and its green spaces have been under threat for decades as new roads and buildings have been constructed. The city's forest cover shrank from 14% to 3% from 1976 to 2000 and its bushland cover nearly halved. Nairobi's diminishing natural habitats has contributed to a growing urban heat island effect and greater vulnerability to rapid flooding as seen in the recent devastating torrential rains.
"At the end of the day, natural habitats remain the best solution to many challenges," says Paula Kahumbu, an ecologist and executive director of Wildlife Direct. "If there could be better urban planning to increase natural habitats and manage urbanisation at the same time, it would be good. It has worked in many cities such as Vancouver, Tokyo, Singapore, Sydney, San Francisco, and Rio de Janeiro. They are surrounded by natural forests with little human interruptions."
Green roofs can be important and effective, concludes Chola, but they are not a panacea and certainly not a corrective to the widespread clearing of vegetation elsewhere.
"I have seen technology trends and industry players come up each time with new innovations," he says of his decades of experience as an architect. "[Green roofs] do have many benefits but they are not always the solution to urban climate challenges."
Gitonga Njeru is a freelance journalist based in Kenya.
