I have loved growing plants since I was a kid. Over the past decade working as an architect in the garden city of Singapore, I have been able to put my passion for plants to use! As an Associate at WOHA Architects, I have had the opportunity to work on a number of intrinsically sustainable, verdant projects at a variety of scales. Some of the most memorable have been a series of bespoke rooftop garden spaces. These range from a rooftop public park to a productive rooftop urban farm, and even the tiny garden at my own apartment.
While designing, building and tending to these gardens, it has been a delight to see these spaces grow and mature. One of the most interesting observations was the transformation that occurs when a planted roof is done right: from superficial green to a thriving rooftop ecosystem. This has led me to reflect on how we can move past just making green roofs, to building ecosystems within our cities.
Greenery has become commonplace in high-rise structures, but it’s often through token green gestures that may not achieve optimal benefits. These are an important step towards reducing pollution, combatting the urban heat island effect, and creating more liveable cities. However, when applied without great care: these sky gardens can deteriorate over time, be difficult to maintain, and fail to contribute towards biodiversity and the success of urban ecosystems.
The following examples show three amazing buildings with sky gardens that don’t act well as ecosystems:
The Interlace, an iconic condominium designed by Ole Scheeren while at the Office for Metropolitan Architecture (OMA), is an innovative typological construction of stacked horizontal blocks that allows great light, natural ventilation, and views from the units. It also allows very generous gardens at ground level, and they are incredible. But above ground, the multitude of green spaces atop the blocks are less successful. The rooftop spaces are largely private, with a large proportion of hardscape and little bits of token greenery. These inhospitable spaces aren’t inviting to people or nature, and it is difficult for plants to thrive among hot patches of concrete.
Moshe Safdie’s residential development called Sky Habitat features an innovative stepped form that creates porosity and outdoor terrace spaces. Three planted sky bridges connect the two towers, creating meaningful recreational spaces for residents. These bridges are quite successful from an urban and programmatic point of view, but are less successful in creating natural ecosystems. The bridge gardens include a lot of hardscape areas, and only contain a few plant species. Without much shade for the hot and windy conditions at height, there’s no way for a microclimate suitable for plant growth to form.
This incredibly successful rooftop public space at Marina Barrage turns an infrastructural blight into a civic space for the city. A green lawn roof slopes from the ground up to rooftop level, providing amazing views fo the city and a great venue for kite flying. It’s a really cool urban intervention- but it’s very hot and unshaded, making it less useful during the day. With a single species of grass covering the rooftop, biodiversity effects are limited.
How can we optimise constructed environments to enhance and augment natural ecosystems?
Using a systems thinking approach, urban ecosystems can be designed to replicate natural ones: so that flora, fauna, air, water, and sunlight are managed in a way that creates a whole better than the sum of its parts. We should encourage biodiversity not just for biodiversity’s sake, but because plants need animals and bugs in order to thrive. Constructed environments can work more like natural ecosystems than you might think!
The examples below show three buildings that are successful in enhancing urban ecosystems:
Nearly a decade since construction, the hanging gardens at Parkroyal Collection Pickering continue to thrive. Lush gardens atop the podium create a favourable environment with plants at the shaded centre of the building, with a carefully sculpted building to allow light and air to pass through. Water features cool the space through evaporative cooling, and encourage a humid microclimate. A wide variety of plant species from shrubs to trees create a variety of habitats and conditions.
The lavishly planted terraces at ACROS Fukuoka slope up gently from the adjacent park, extending the natural environment for plants, animals & people. A diversity of local plant species promote biodiversity, and deep planting allows large scale trees to provide plenty of shade. Rainwater drainage trickles down the building like a natural stream, providing drinking water for birds and insects, and further encouraging biodiversity.
The enormous planted facade and sky terraces at Oasia Hotel Downtown provide 10 times as much green area as if the site was left empty. Over 50 types of plants has led to vegetative resilience. Even though it’s in the middle of Singapore’s dense downtown, the structure has attracted a surprising amount of urban biodiversity, including rare migratory vultures from the Himalayas!
How can we Build Urban Ecosystems?
1. Reach a Critical Biomass by including enough planting density and soil depth to sustain growth and counter the urban heat island effect.
2. Integrate Natural Water Features to reduce temperatures through evaporative cooling, increase humidity, and provide habitats and drinking water to encourage biodiversity.
3. Include a Diversity of Plant Species in order to allow mutually beneficial relationships to form and increase habitats for birds and insects, reducing pests.
4. Encourage Biodiversity by creating ideal habitats and micro-habitats to attract wildlife, and through plant selection, providing benefits for the immediate space and for the larger environment.
5. Craft a Microclimate by ensuring shade and adequate climactic conditions, with the building form, water elements, and plants of a variety of scales.
The following projects that I’ve recently completed show how these principles can be used to build rooftop ecosystems in urban locations:
WOHA Rooftop Urban Farm
When we first started experimenting with growing edible plants on the rooftop of the WOHA office, we started with a small area of planters and grew a single species at a time. Without achieving critical biomass, the air was very dry and the plants would wilt on hot days. We also had significant problems with pests, which will quickly devour through a monoculture crop.
After little success with our initial experiments, we redesigned the rooftop to create an edible ecosystem. Water features reduced temperatures through evaporative cooling, increased the humidity of the air, and provided habitats for insects & places for birds to drink. We also began to cultivate edible fish, and used an aquaponics system to fertilise plants with fish waste, creating a closed loop nutrient system.
With more than 100 edible plant species, a critical mass of plants and soil helped to create a humid microclimate where the plants began to thrive. With a multitude of species bringing in various types of beneficial insects and birds, we no longer had any pest problems. With a canopy of creeping vines above and medium sized fruit trees providing shade, a lower layer of smaller plants can thrive in the harsh rooftop conditions, acting similarly to the layers of a rainforest.
It was exciting when we realised that new plants started popping up on the rooftop, and we realised that wild birds had been transporting them from the nearby public parks and from the hanging gardens at Parkroyal Collection Pickering, showing that a little green space can contribute to the overall health of natural ecosystems in the city!
Design Orchard
The highlight of this mixed use building along Singapore’s famous Orchard Road is the rooftop public space. The building was designed in a wedge shape, in order to make the rooftop feel like a hilltop park. This also makes the space highly visible and inviting from street level.
The slope was used to form an amphitheatre facing back towards the city. To provide shade, lush planting is used to cocoon the public space with plants and trees. The majority of the planting is done in a 45cm deep planter bed, with oversized precast upturn concrete pots used to create soil depth for large trees.
Rainwater from the uppermost sloped roof falls through a series of rain chains into giant water pots, which are filled with lotuses and mosquito fish, and birds are often found drinking from the water. The water is then filtered through the planters and collected in a tank to use for irrigation.
Around 50 plant species were used, many of them local species and species which attract butterfies and birds. The lush tropical landscaping has begun to take over, and it really feels like a hilltop park resting on top of a building!
Inside Outside Penthouse
When it came time for me to design my own apartment, I wanted to adapt these concepts for a smaller scale. My tiny 1,000 sqft apartment (including 2 balconies and a roof terrace) is special because each interior space looks into an adjacent outdoor space, and I designed the interiors to accentuate this. Because of the compact size, the garden spaces needed to have a lot of impact.
In order to maximise the number of plants, creative space saving techniques had to be used. Planters were lifted up above usable areas, a steel mesh wall for creeping vines, a green wall, and a planted pond were used. Loose pots helped to fit in even more plants into every nook and cranny, and I was able to fit more than a hundred plant species!
On the rooftop, a built in pond instantly cooled the space through evaporative cooling, and increased humidity. The thermal mass of the water creates a noticeable reduction in temperature throughout the day.
During construction, the plants that I had on standby could barely survive the heat of the rooftop. After a few months of growth, the rooftop had its own cool and humid microclimate where plants began to thrive!
Even in such a small space, an astounding amount of biodiversity began to show up in my garden. Organic waste from the kitchen and leaf litter is used for fertiliser, and the garden has continued to grow well on this closed-loop nutrient system.
On an even smaller scale, I filled my bedroom blacony with potted plants, including a large ceramic dragon pot filled with water lilies and fish. Before there was a water body and critical mass of plants, this balcony was blazing hot and no plant could survive, even when watered every day. After a variety of plants was brought in and the space was cooled evaporatively, these plants all survive on rainwater without any additional watering.
Rather than trying to force plants to grow on a building, we should think of buildings as part of larger natural ecosystems so that they can thrive. Various elements of green roofs can support each other in mutually beneficial ways, creating an environmental critical mass that allows a self-sustaining ecosystem to form. By reaching a critical biomass, integrating natural water features, including a diversity of plant species, encouraging biodiversity, and crafting a microclimate; we can replicate natural ecosystems in our urban cities!
Images by Jonathan Choe
