The Flowering Roof
Grow a garden or a lawn on your terrace to beat the heat, but do not neglect maintenance issues.
With the summer temperatures soaring high, everyone dreams of cooler homes. Air conditioners could be a solution, but we now know that they are not a solution, but a villain.
For innumerable reasons like the way they transfer indoor heat to outside increasing city temperatures, dilute our biological capacity to live with seasons, health problems due to moving across high and low temperatures, artificiality of air, poor indoor air quality, power consumption, electricity bills and such others, AC has proven to be anti-environment and anti-health.
Given this, there has been increased search for simple and natural solutions. One among them is a green roof, not growing vegetables in trays, but having greenery all over. Imagine a roof where we see no concrete, but only grass! It increases thermal mass, delays surface run-off and works with minimal maintenance.
An intensive green roof needs to be structurally designed for load, or if we plan to grow on the existing roof, a qualified engineer can assess its feasibility. In case roots attempt to penetrate the concrete, a root barrier layer of High Density Polyethylene (HDPE) or any other suited sheet can be laid, though the best is to ensure that shallow rooted plant material are chosen. Additionally, HDPE also ensures water proofing.
Above the root barrier, a drainage layer is needed with half-inch of gravel and a layer of sand above it. To ensure the mud does not slip into this layer but only excess rain water does, we can use the costlier but more long lasting geothermal fabrics or simply save money by using shade nets. They let water down but not the soil. Finally, we need red soil, manure media or mud mixed with perlite, vermiculite or coco peat. While all these are suited for plant growth, the decision may depend upon possible roof load, maintenance issues or available water.
Typically, the soil layer can be 4 to 8 inches thick based on plants’ type. Parapet wall height may have to be adjusted to take the terrace garden and multiple drain holes will be needed compared to what we normally provide. Drip irrigation can be implemented in case of large roof areas.
While lawn would be the choice of most people, it demands much water and maintenance, besides many turf varieties not being suited on the terrace. In case of good sunlight, Bermuda, Doob or Korean grass may work, if not St. Augustine may have to be preferred. If the terrace has occasional use, hardy creepers like Rangoon creeper can enliven the surface with its seasonal flowers. With good drainage, ground hugging shrubbery and small water succulent plants can also be considered, which may be easier for de-weeding.
Tray-based roof garden is more popular considering the variety of vegetables one can grow and manage rain water harvesting as well. However, everyone cannot spare time to that end, but everyone can enjoy a lawn or a creeper bed on the terrace.