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Agriculture with Altitude

 Gone are the days where the height of urban living was overlooking the city skyline as you frolic in a penthouse pool. There’s a fresh green alternative that has taken Europe by storm. Introducing the Green Roof! This climate friendly movement strives to transform every bleak urban rooftop into a flourishing hub of greens, biodiversity, and energy efficiency. According to greenroofs.org, a green roof system is an extension of the existing roof which involves, at a minimum, high quality waterproofing, root repellent system, drainage system, filter cloth, a lightweight growing medium, and plants.

Figure 1: Rooftop farming in Brooklyn

Green roofs offer numerous benefits to the environment and our wellbeing by aiding stormwater management, providing seasonal insulation, and cooling, improving air quality, increasing biodiversity, and giving city dwellers the opportunity to learn about urban farming and grow their own greens.

Now, if you are a conscientious critic you are probably wondering how green roof technology benefits the environment and to what extent. One of its most distinguished services is stormwater management. The rainfall is stored by the substrate and used by the plants where it is released back into the atmosphere via transpiration or evaporation. In the summer, green roofs can retain 70-90% of rainfall and in the winter: 25-40%. Furthermore, rooftops are the site of the highest temperatures in the summer and the highest heat loss in the winter. Fortunately, green roofs are effective insulators during winter, and competent coolers in hot summer months; a natural energy-saver. Through the daily dew and evaporation cycle, plants can cool cities during summer months and reduce the Urban Heat Island (UHI) effect. Better yet, Green roofs improve air quality by capturing airborne pollutants, deposition, and filtering noxious gases. The temperature-moderating effect of green roofs can reduce the demand on power plants, leading to a reduction in their greenhouse gas emissions. Next, who doesn’t like the sound of birdsong in the morning? Green roofs can sustain a variety of plants, insects, and provide a habitat for birds. Migrating Birds use green roofs as a rendezvous point; meaning rooftop habitats can link together bird species which would otherwise be fragmented. Green roofs are also a site of learning, offering practical knowledge of urban agriculture and educating children raised in cities who wouldn’t otherwise have clear comprehension of how food is produced.

Figure 2: Urban Farmers at Nature Urbaine

In fact, France recognised the environmental benefits of green roofs so much that, in 2015, a law was approved by Parliament which decreed that every new building within commercial zones had to be partially covered with either plants or solar panels. Now Paris boasts the world’s largest urban farm in the world Nature Urbaine. Nature Urbaine spans 14,000 square metres, about the size of two football pitches. Although it has only been fully opened since July 1st 2020, it is already supplying local residents, who can order fruit and veg boxes online; a cluster of local hotels; and a private catering firm that runs 30 company canteens in and around Paris. Locals to this mega green roof can also rent one of the 140 allotment plots for €320 a year; an amazing opportunity for those who want chemical-free fruits and vegetables whilst supporting the green roof movement!

So how can you support the green roof movement? By installing one of course! There are two types of green roofs: extensive green roofs and intensive green roofs. Extensive green roofs are lighter; require little maintenance and have no need for additional watering. Extensive green roofs are suited to smaller vegetation of around 80-100 mm like small flowers. Whilst Intensive green roofs are designed to support larger flora such as bushes, trees, and a wider variety of plants. Installation itself has only 5 manageable steps.

Step 1: Waterproof your roof deck using concrete or screed.

Step 2: Install a root barrier. Roll out the plastic root barrier across the length of the roof, cut to size, and seal with tape where necessary

Step 3: Install green roof drainage membrane. After installing the root barrier, extend the green roof drainage membrane across the length of the roof.

Step 4: Grow substrate. The substrate is typically some form of aggregate and organic material combination. Spread it evenly across the entire roof.

Step 5: Finally plant your seeds or plants!

Whether it’s the health appeal of locally grown greens or the extensive benefits to the environment, we can all reap the benefits of green roofs. The bottom line is that it positively affects people and the environment. Let’s turn every grey-gloomy rooftop green.