Lai See | Green roofs look better while saving money and water

In one of those curious twists of fortune, Sean Johnstone came to Hong Kong in 2011 with Japanese steel giant Kawada Industries to compete for contracts to supply heavy steel for Hong Kong infrastructure projects. That exercise was relatively unsuccessful as the Japanese currency, at 76 yen to the US dollar, was the strongest it had been for many years.

Now Johnstone spends his time marketing a sustainable roof greening system but is still working for the steel company. Johnstone is the general manger for Kawada's overseas operation and in the course of his presentations here would mention almost as an aside one of Kawada's green initiatives, Midori-Chan, which has been operating in Japan since the 1990s. It is a patented system designed to maximise vegetation growth and recycle waste, while dramatically minimising water usage.

It came about as a combination of concern over the huge amounts of formwork the company was paying to have taken away after casting steel, together with a CSR initiative. The formwork was reduced to a mulch and formed the basis of Midori-Chan.

The interest in Hong Kong was to use it to provide "greening", particularly for roofs. In an attempt to encourage green buildings the government will allow developers a bigger gross floor area if they can fulfil various requirements, one of which is a green roof. There are a number of competing systems but the standout feature of Kawada's is that it requires virtually no maintenance. So the garden is watered when it is set up and then requires no further watering. It might require weeding once or twice a year.

While the upfront costs may, though not necessarily, be higher than other systems, costs fall dramatically over the life of the garden since there are virtually no maintenance costs, nor is there a need for costly irrigation systems.

"Over a 10 year period a 100 square metre roof from a typical system will use 2.5 million litres of water, while our system will use 2,000 litres," says Johnstone. Tests show that Midori-Chan uses 0.17 litres per square metre per month, while some Hong Kong government specifications for green roofs specify 190 litres per square metre per month.