Someone raised a question today about what could be the most sustainable planting strategy for green roofs in India?
This is what we think. If maintenance is no problem and a sustainable water source is available (treated used water), we actually prefer to install lawns on a roof. Some might argue it is not a greenest choice due to the water scarcity & hot climate of India, we actually think otherwise. We provide green roof and living wall systems under our brand BuildScape and we have found that there are three main reasons why someone would install a green roof:
- Usable Amenity Space
- Heat Mitigation
All other benefits are important but not the key drivers in the decision making process. There is no doubt a lawn looks good and allows for building occupants to regularly use the vegetated parts of the green roof. But more importantly, the regular watering that a lawn requires actually cools the roof slab below and provides radiant cooling to the occupants below. The evaporative cooling of the surroundings and the heat island mitigation is also far higher through a high moisture green roof.
We have also found that using highly drought tolerant species actually has a negative impact. The growing medium acts as a thermal mass which has a negative impact on the energy usage in the spaces below.
As far as irrigation is concerned there is always scope for automation. Water can be obtained by simply treating the grey water in the building using a small REED bed system. The lawn on the roof does not need high quality water and semi treated grey water is perfect to water a green roof.
We have a tried different kinds of plants on the roof at our office.
Nothing has improved the comfort conditions more than a well irrigated lawn on the roof. We use a small REED bed to treat the grey water and use this treated water to water our green roof and living wall systems. The water smells odd but we have not needed to use even a drop of manure or any other chemical to keep our green roof thriving for the last two years.
The value of using drought tolerant species on a roof is over rated, at least in cooling dominated climates like India. Concepts like Xeriscaping are better suited and are the more sustainable method for ground landscaping.