Green Roofs: Ideal for Green Building in India?
Green roofs have become a very important component of sustainable urban development within the last 30 years. Their striking economical and ecological advances, along with growing environmental awareness, are the driving forces for this great success. At present, green roofs and rooftop gardens can be found in most big cities around the world, benefiting the urban environment and its inhabitants. Green roofs have yet to catch on in a big way in India, but hopefully this will change soon.
The Benefits of Green Roofs
Many building design professionals around the world have hugely underestimated the the value of green roofs. Especially in warmer countries like India, a well-irrigated green roof can provide greater energy savings compared to a cool roof or even an insulated roof. According to the premier green roof industry association, "Green Roofs for Healthy Cities", the benefits of green roofs are:
- Energy efficiency - Through greater insulation offered by green roofs
- Improved health and well being - The reduced pollution and increased water quality from green roofs can decrease demands on the health care system
- Urban agriculture - Green roofs can be used to set up small organic food gardens
- Roof durability - By preventing large temperature variations, roofs are less likely to crack
- Fire retardation - Green roofs have a much lower burning heat load in comparison to conventional roofs
- Reduction in electromagnetic radiation - Green roofs are known to reduce the electromagnetic radiation from wireless devices by 99.4% (Herman 2003)
- Noise reduction - Green have excellent noise attenuation and can reduce noise penetration by up to 40 decibels
- Enhanced marketability - Green roofs add value since they are one of the most identifiable features of a green building
- Increased biodiversity - Green roofs can sustain a variety of plants and invertebrates, and provide a habitat for various bird species
- Aesthetic Improvement - Green Roofs are visually enhancing the quality of city life
- Waste diversion - By prolonging the service of the HVAC equipment through decreased use
- Storm water retention - A 6-inch green roof can hold up to 50 mm of rainfall. It also delays the runoff, reducing the pressure on storm-water drains
- Urban heat island effect - Through daily evapotranspiration, plants cool the city in the hot summer months
- Improved air quality - The plants on green roofs can capture airborne pollutants and atmospheric deposition, as well as filter noxious gases
- New amenity space - Green roofs can positively affect the urban environment by increasing amenity and green space
How Does a Green Roof Work?
Green roofs are comprised of a number of different layers, all of which have different and related functions that have to work together to function properly. The green roof must consist of at least the following layers to be effective, durable and safe:
- Concrete finish
- Root barrier
- Drainage layer
- Geotextile filter
- Light weight & water retaining growing medium
- Plants (grass, sedums, aliums, herbs etc)
No green roof is maintenance-free. It requires regular irrigation and periodic trimming, weeding, fertilizing, termite checks, etc. The regular irrigation actually adds to the general cooling of the surrounding and the building. Hence, it is important to identify a sustainable water source, such as treated waste water or harvested rainwater, so that the green roof can be kept moist without compromising the quantity of fresh water available to the building occupants.
The most common question people ask about green roofs is "Doesn't it leak?". Well, the answer is absolutely not, provided the roof has been designed and installed by qualified professionals who understand the relationship between the green roof and the building.
The waterproofing ensures that no moisture penetrates the roof surface. Even if the waterproof layer fails, it may not necessarily be a cause for concern in concrete structures. In a green roof, all moisture retention and organic activity is happening an inch above the surface of the roof, separated by the drainage layer. So essentially the waterproof layer and the green roof are separated by an air gap, which ensures that any additional water simply flows away through this layer just like it would in a conventional roof.
In fact, there is a smaller possibility of moisture penetration through a green roof, since the waterproof layer is well protected from the fluctuating environment outside and lasts longer. Hence, building owners should be less worried about moisture penetration if they have a green roof (compared to a conventional one).
My Own Experience with Green Roofs and Living Walls
In 2010, we installed a green roof at our office in Coimbatore, Tamil Nadu. Its purpose was only to add a unique feature to our building. Soon, we noticed that the green roof had improved the comfort conditions in the office far beyond our expectations. We also noticed that this improvement in performance was achieved by keeping the roof well-irrigated. The moisture kept the building cool even when the temperatures outside were close to 40 degrees Celsius.
We decided to do more with this idea, and after more than a year of trying different plants, growing media, filter geotextiles, and finding the best drainage layer and waterproofing, we created the right formula. We then launched our green roofs products with the brand name BuildScape. BuildScape now undertakes projects offering green roofs, living walls, bio-walls and auto-watering pots for the Coimbatore market.
I soon found that birds and squirrels loved the roof and often quarrelled with each other for their share of the green space. I then found myself taking evening naps after work on the grass on the roof. Now, whenever the weather allows it, I take my laptop out to the roof and work from my own private garden.
I then realized that I loved spending time on the green roof, so maybe I could start gardening. So, I relieved my gardener of his duties and took the maintenance of the roof into my own hands, which includes composting all our kitchen waste to create manure and the other activities listed above.
I am now a part-time business owner, a part-time green building consultant and a part-time gardener.