Green roofs haven’t been in the news much lately.
But that doesn’t mean that they’re not being built nor does it mean they aren’t being improved.
Perhaps it’s the mass media’s constant quest for something new and different that has kept green roofs out of the news.
Certainly, research continues, often with interesting but not sensational results.
In the Netherlands, a new design for green roofs was unveiled last month, when Joris Voeten, an urban engineer with a company called Urban Roofscapes in Amsterdam, presented the world with a design that he says stores more rainwater than existing green roofs. He also says it requires less power for irrigation.
The system makes use of sensor technology. Sensors are embedded in a shallow layer of soil on top of the roof’s water-storage elements.
The sensors constantly monitor the surface air temperature and the moisture content of the soil. If the soil becomes too dry an automated system can add water.
And if there is too much water, it can be released into the drains.
The system stores water in the insulated layer below the soil. Capillary action draws the water upward to irrigate the plants’ root systems. It works much like the old-fashioned kerosene lamps one used to see in rural areas. In those lamps a flat woven cotton wick extended down from the burner into a reservoir of kerosene.
Green roofs produce a cooling effect on buildings and the air immediately above them in two ways. The plants reflect heat instead of absorbing it the way traditional roofing sheets do. They also reduce heat by evaporating water.
Robbert Snep, of Holland’s Wageningen University, notes that the cooling effect of green roofs is well known but says Voeten’s roof is an improvement on existing designs because of the way it stores water and the way that water can be fed back to plants.
The use of sensors makes his green roof a smart roof.
“The smart roof really ensures that there is evaporation during heat waves for example,” Snep says. “That’s how they cool the surroundings. People can sleep well and…work well in such an environment.”
Voeten says his system can be laid on any flat roof with sufficient load-bearing capacity. The cost, he says, is likely to be somewhere around €100 to €250 per square metre. That works out to about $175 to $265 per square metre in Canadian currency.
Whether that price will be a stumbling block remains to be seen.
Certainly, in the early days of green roofs the cost of additional load-bearing capability and the cost of maintaining the roof slowed acceptance.
But green roofs in one form or another have been around for centuries. In northern Scandinavia sod roofs were commonplace. The modern trend started when green roofs were developed in Germany in the 1960s. Now it is estimated that about 10 per cent of all German roofs have been “greened.”
Apart from Germany, several other European countries have active associations promoting green roofs, including Switzerland, Norway, Italy, Austria, Hungary, Sweden, the Netherlands, the U.K. and Greece. The city of Linz in Austria has been paying developers to install green roofs since 1983.
Today, about 10 million square metres of new green roofs are being built worldwide every year, and Germany continues to lead the way.
Nearly a third of all German cities have regulations to support green-roof and rainwater technology.
Reducing the cooling and heating loads of buildings by using green roofs is an idea that appeals to building owners and operators. But as a warming world makes aberrant weather more common, green roofs will become more appealing as a useful tool for stormwater management.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to email@example.com.