What are Green Roofs

Green roofs or living roofs have been around for hundreds of years. In Scandinavia one traditional form of roof has been the sod roof where a house is half buried and turf is put on the sloping roof. By burying the house and turfing the roof the Scandinavians used insulation to survive the long, cold winters of the north. The modern green roof was invented in Germany in the 1960s.

A green roof is neither a roof that is painted green nor a roof with a few potted plants on it. Rather a green roof refers to a roof that has grass, trees, shrubs and plants growing in soil on the roof. There are two basic types of green roof: intensive and extensive. An intensive green roof has a substantial layer of soil and typically is like a mini park where trees, food, plants and shrubs grow. There is often also a pond on intensive green roofs. The advantage of the pond is twofold – it increases the diversity of the roof’s ecosystem and it allows grey water recycling. An intensive green roof requires considerable strength to support the weight of trees etc., an irrigation system, a drainage system and a waterproof membrane to protect the roof underneath from water damage. Intensive roofs need considerable management to keep up.

An extensive green roof has less soil and lighter plant life. A waterproof membrane is still necessary but not irrigation and drainage systems. Normally an extensive green roof (once established) will be self-sustaining, taking what it needs from rain water and the biodiversity that it attracts.

There has been a lot of research done into the benefits of green roofs. There are a number of benefits to green roofs. These are:

• Reduced heating costs. Green roofs provide insulation or increased thermal resistance, letting a house keep its heat better.

• Reduced cooling costs. This is due to evaporative cooling from the green roof. A green roof can reduce cooling costs by 50% to 90%.

• In cities, it has been shown that green roofs help to lower the average temperature in the summer because the green roof is better at absorbing heat than concrete etc. that merely reflects heat and causes the ‘heat island effect’.

• Green roofs use rain water and stops storm water run-off from overloading city drainage systems during heavy storms.

• Green roofs create habitat for birds and insects.

• Green roofs help to combat carbon emissions and they filter the pollutants out of the air.

• Green roofs also act as insulation against noise pollution.

• Another benefit is that food can be grown on green roofs.
  

Although it is not cheap to retrofit green roofs on homes, they have a great number of benefits. 10% of buildings in Germany now have green roofs. For architects, designing buildings with green roofs not only earns LEED points for the project but also drastically reduces the running costs of a building. As with many sustainable housing ideas such as super insulation, photovoltaic panels, programmable thermostats, awnings over southern facing windows and compact fluorescent light bulbs the cost of green design is soon paid for many times over by the savings they engender.