Green Roofs: The History of a Modern Spin on an Ancient Technique
While green roofs have become popular in recent decades, they existed in other forms for centuries. This trend of repurposing urban space, though a creative way to help fight climate change, is not as new as it may seem.
Green roofs of all varieties cover the globe. Some estimates guess that nearly 15 percent of roofs are green roofs in Germany, for example, and that number is growing. But where and when did they originate? Who figured out that adding a layer of vegetation to a roof could dramatically reduce a building’s energy consumption? Or that it could mitigate urban flooding caused by rainwater surges while providing an alternative use of space where open areas are rare? Like with many innovations, the conception of green roofs is not easily denoted.
In some ways green roofs have existed for hundreds of years. Sod roofs have been used in Europe, mostly Scandinavia, for centuries and across the American Great Plains since the 1800s. Builders with limited resources would cut up large areas of grass and place it along with the dirt it was rooted in across the roof of a small building as pictured below. This sod roof served as a strong insulator, making the home it covered cooler in the summer and warmer in the winter long before the convenience of modern heating and cooling.
Though modern green roofs were not directly inspired by these traditions, they hold similar benefits, like providing insulation. The green roofs that dot city rooftops across the globe today originate from German research conducted in the 1960s. This research was spearheaded by Reinhard Bornkamm from Berlin’s Free University when he was looking for a way to reduce storm surge flooding in cities. Though Bornkamm published his research in 1961, the market for green roofs in Germany truly grew in the 1980s and 1990s with the help of incentivizing legislation that provided an allotted number of Deutsch Marks for each square meter of green roofs built. In 1989, Germany had one million square meters of green roofs installed and just seven years later, in 1996, that number grew monstrously to ten million.
Germany further asserted itself as a green roof innovator when it established the first widely recognized set of green roof guidelines in 1982, abbreviated in German as the FLL or the German Landscape Research, Development and Construction Society in English. These guidelines provided information on adequate drainage materials, plants that tend to thrive and strategies for waterproofing roofs.
Green roofs came to and grew in popularity in the United States later than in Germany and the rest of Europe so, consequentially, the US lacks the extensive research and information that the FLL provides. While the FLL can still be useful for American designers, some have argued for more research tailored specifically to American environments so that each individual green roof construction project in the United States requires less original research and testing.
Still, green roofs in the United States are growing in popularity at a rapid pace. This surge was partially motivated by the increased discussion of and attention to urban heat island effect. After a number of people died as a result from a heat wave in Chicago in the summer of 1997, more urban leaders took action to mitigate this overheating by promoting green roofs.
Since then, many municipalities in the United States have started initiatives to encourage the building of green roofs. In New York City, for example, a city made up of approximately 72 percent impervious surfaces, PlanNYC 2030 was created to decrease the proportion of impervious surfaces in the city through building green infrastructure like green roofs. This is with the intention to mitigate storm runoff which will likely increase in the coming years due to climate change.
Though this initiative, and many others, to build and promote green roofs is motivated by the goal to lessen heat island effect and to decrease the amount of storm water runoff that floods sewers regularly, the action has broader effects too. Because green roofs act as insulators they decrease the energy needed to heat buildings in the winter and cool them in the summer. This reduction of energy use, though small for an individual building, can add up to much larger when an entire city is covered in green roofs.
With the growing attention to climate change, heat island effect and storm surges, as well as the benefits of green roofs, industrious entrepreneurs have been able to create a private green roof market for themselves. This is most evident in the outcropping of green roof design companies that cater to residential and institutional buildings alike in New York City. In the past ten years, over ten new green roof design companies opened in the city that once had only a handful.
Though green roofs today are the epitome of innovative uses of space and clever strategies to fight climate change, their history is long. Dating back centuries, green roof have provided insulation for building making the technology as it is today a modern repurposing of a longstanding technique.
