The new industrial buildings in the city of Stuttgart have vegetalized roofs. 50 % of them are paid for by the city. Between 1995 and 2005, 10 % of newly built German roofs were « vegetalized ». Today, 40 % of German cities finance the technique to encourage its development. Vegetalized roofs are good thermal insulators. A study of the city of Toronto revealed that if 6 % of the total available roof surface area was vegetalized, the temperature would go down by between 1 and 2 °C in summer and the electricity demand for air-conditioning would be reduced by 5 %. Vegetalized roofs also regulate the flow of rain, absorb some air pollution and encourage biodiversity.