10 Reasons Why Green Roofs Are The Wave Of A Climate Resilient Urban Future
An ancient technology brings a host of benefits to help cities become more climate resilient.
Once upon a time, innovative builders used overlooked roof space for gardening and irrigation. This was long before tractor-trailers and paving machines could’ve done such a job. Some of that roof space still stands high above a canyon in the Peruvian Andes.
I’m talking about Machu Picchu, built before Columbus reached the Americas and colonization overtook the world. The Incas used a technology that should be used on every street corner around the world:
Green Roofs Have Not Progressed Much Since The Incas
The Incas may have mastered green roofs long ago, but until recently, green roofs were far from global. Scandinavians have used thick sod roofs for centuries for thermal regulation; imagine braving those long, cold winters without modern heating! And many of our ancestors put vegetation on their shelters to keep cool when it got warm and keep warm when it got cool.
The first wave of modern green roofs arose in Germany in the 1960s. German research Reinhard Bornkamm published his work on green roofs in 1961. That coincided with a period of technical research on the different components of green roofing technologies.
As one paper recounted: “The development of green roof markets in Germany expanded quickly in the 1980s, with average annual growth of fifteen to twenty percent. By 1989, 1 million square meters of green roofs were installed in Germany. By 1996, this number had ballooned to 10 million square meters. This remarkable growth was encouraged by state legislation and municipal government grants.”
In Germany, more than 14% of all roof area is green. Cities like Singapore, Vancouver, and Chicago have also led the way on green roofs. But these places are outliers; in most of the world, green roofs are more of a novelty than a common sight.
Urbanization Gives Green Roofs Great Potential To Make A Big Difference
When Macchu Picchu, the human population was a fraction of what it is now — a few hundred million. Few lived in big cities.
Now, eight billion people roam the Earth, and most of them live in densely populated cities. Of all the notable societal trends of recent times, urbanization is one of the most defining. Urban populations are burgeoning and will mushroom going forward.
Unlike their rural counterparts, many of those urban residents live in big buildings with large roofs. These buildings are an overlooked but key piece of the climate change puzzle. According to the United Nations Environmental Programme, buildings and their construction account for almost 40% of global greenhouse gas emissions. We could view this as a risk to future climate mitigation efforts or we could see it as a golden opportunity.
One of the easiest ways to make buildings green is to make their roofs green. As you’ll see below, there are different paths to doing so, but the end results are quite beneficial across the board — for the people who occupy buildings, for the bottom lines of all sorts of building-related businesses, and most importantly for the planet.
How Roofs Can Go Green
One way to categorize green roofs is by the depth of their respective planting mediums. Extensive green roofs are shallower. As such, they’re more common for single-family or multi-family residences. Given their lower depth, extensive green roofs lend themselves to plants that have shallower roots and require less water, like drought-tolerant sedums (i.e. succulent plants) and grasses. These roofs are lighter on the wallet and physically lighter on the buildings they cover compared to their deeper counterparts: intensive green roofs.
Intensive green roofs give commercial building operators flexibility to really make their green roofs shine. They’re heavier and more expensive, but they allow for greater biodiversity and more offerings for the humans who live and work below them. Flowers and trees give pollinators and other creatures a welcome escape from the concrete jungles that often surround these intensive green roofs. Amenities like pathways, benches, and tables make these roofs human-friendly too. As such, intensive green roofs are often called “rooftop gardens.”
The steps to turn a green roof from an idea to an actuality are simple but not always easy to implement. First, approval to build a green roof must be verified. Certain types of real estate, like co-ops and condos, may involve more red tape if the party that owns the roof isn’t the same party that maintains the roof (often management).
This clash between regulations, developers, and other involved parties can get messy if not handled properly. Furthermore, the decentralized nature of governmental decision-makers who can influence the necessity (by regulation) or, conversely, the degree of difficulty (also by regulation among other means) of enacting green roofs can make it hard for businesses large and small to understand what they can and cannot do.
If that hurdle is cleared, builders must evaluate what type of roof can be built given the building structure among other factors. Then, aesthetic and engineering questions enter the scene. And I haven’t even mentioned perhaps the biggest hurdle of all: money.
Alternatively, green roofing can be incorporated into construction planning before the property is even built. That gives all stakeholders a chance to provide input and execute on a vision of a green roof hand-in-hand with turning a blueprint into a building. For something like a green roof, it’s easier to start at the drawing board rather than going back to the drawing board.
After all, it’s one thing to recreate the natural environment on the ground. It’s another thing altogether to do so in the air.
But as you’ll see below, green roofs are well worth the costs.
In urban areas, structures like buildings and roads absorb the sun’s heat more than natural features like plants and water. The resulting urban heat island effect can make cities feel much warmer than surrounding areas. By replicating more natural patterns of solar absorption, green roofs help reduce the urban heat island effect. As extreme heat frequency rises in dense cities across the world, city dwellers will look for every bit of cooling they can find. They should look no further than the roofs over their heads.
Piggybacking off the urban heat island effect, green roofs reduce energy costs by absorbing solar energy and providing natural building insulation. This natural protection against extreme heat extends the lifespan of green roofs, helping them last twice as long as traditional roofs. Even six inches of green roofing can save 75% of a building’s summer energy costs. So in addition to cooling surrounding areas, green roofs cool buildings too. And this lowered need for air conditioning leads into another benefit: pollution mitigation.
Air Pollution Mitigation
With energy conservation comes less pollution. But even better, since green roofs consist of plants, they remove particulates from the air. In cities with frequent air quality problems (like Mexico City, Sao Paulo, and Shanghai among many others who often have high levels of dust and smog), this is particularly impactful. And given what we’ve learned about the public health impacts of air pollution, this cannot be understated.
Not only do the plants on green roofs absorb particulates, they absorb the biggest cause of the climate crisis: excess carbon dioxide in the air. One study from China indicates a simple green roof can absorb 1.79 kg of CO2 per square meter annually. On a 1,000 square meter urban green roof, that translates to almost two tonnes of annual carbon dioxide absorption.
Traditional roofs shed water, potentially overloading city streets during major storms. A typical city block generates five times more runoff than a similarly sized woodland area. As climate change amplifies the frequency and severity of storms, urban runoff will become increasingly harmful.
Green roofs retain up to 90% of summer precipitation and 40% of winter precipitation. By absorbing water, green roofs help ease the strain on city drains and pipes. This significantly lowers the risk of flash floods and another aspect of modern cities: water pollution.
Water Pollution Mitigation
When rain falls in cities, it carries pollutants into groundwater, which then ends up in rivers and lakes. Green roofs filter rainwater and remove toxins, thereby reducing the risk of water contamination. In a world where almost two million people die every year from drinking contaminated water (and where climate change will make water increasingly scarce), green roofs can help cities sustainably provide as much clean water for residents as possible.
Many urban residents lack reliable and affordable access to healthy foods. Green roofs can be used to grow produce. This is harder and more expensive than implementing typical green rooftops, but it gives residents safe, cheap food right in their vertical backyard. It also has a double benefit for the planet: locally grown food does not need to be transported or refrigerated, making it much less greenhouse gas-intensive than alternatives (and easier on the wallet).
One of the greatest areas of opportunity in public health is to leverage nature to easily improve health outcomes. Hospitals have adopted this insight to improve COVID-19 outcomes, for instance. Green roofs can boost the physical and mental health of city residents. Being near greenery improves your memory, reduces your stress levels, and lowers your blood pressure among other physiological benefits.
Exposure to greenery even makes children smarter, according to a study conducted by Spanish researchers. If that doesn’t convince parents and policymakers alike to push for green roofs, I don’t know what will!
Greenery deprivation is sadly far too prevalent in urban areas across the world. People deserve access to nearby green open spaces; it directly helps them and indirectly helps the rest of us.
Furthermore, green roofs provide easy opportunities for neighbors to socialize. As we reckon with a global loneliness epidemic that COVID has only exacerbated, we cannot overlook these quick wins to make people happier and healthier.
By giving native species green spaces to roam, green roofs boost biodiversity in urban areas. Planting a diverse range of species can attract a variety of fauna like butterflies and beetles. It’s not easy to design proper habitat with a green roof, but the benefits can be immense if done right.
Green roofs are especially helpful for promoting the biodiversity of endangered pollinators. We have selfish reasons to protect pollinators — we really need the birds and the bees for our food supply!
Let’s imagine you’re looking for a house to buy. You have two options in mind that you like equally before you consider one factor: one house has a solar roof but the other doesn’t. Assuming the houses are equally priced, you’ll buy the house with the solar roof, right?
Well, the same principle applies to green roofs. We don’t have a lot of published research to draw on to back this claim, but researchers at the University of Technology Sydney found increases in residential property values of between six and 15 percent thanks to green roofs.
As city planners look to augur a greener future, green roofs represent a straightforward, multipronged approach to climate resilience in urban areas. They’ve been around for millennia but have never achieved the broad-scale adoption that would make them a ubiquitous instrument of improving climate resilience in cities. They bring a host of complimentary benefits — pollution mitigation and carbon sequestration among many others — that reflect a holistic, equitable approach toward keeping cities cool and clean.
And let’s not forget green roofs are both green for the planet and green for the wallet.
Future Proof Cities is a Medium publication by Wavin. Danny Schleien writes for the publication as an independent writer.