The city of Linz in Austria consists of a building area of 3,600 ha. The local authorities introduced suitable building plans in 1985, which basically were legal means towards the implementation of green roofs. The most important elements of these plans were that the green roof construction has to consist of a vegetation layer (above the drainage layer) with at least 8 cm for extensive green roofs and from 15 to 50 cm for intensive green roofs. Additionally, the coverage vegetation should extend of at least minimum of 80% of the total roof area. However, this plan also identified areas where it was mandatory to build green roofs such as roofs of subterranean parking or underground buildings or areas of mixed use and where expansion is limited. In particular, green roofs were mandatory for new buildings with a surface more than 500 m2 and where extensions to existing buildings larger than 100 m2. Also, it was mandatory for new residential buildings and new industrial/commercial buildings with a surface larger than 100 m2 and 500 m2 accordingly[1]. The results of this scheme for the time period 1989-2005 are illustrated in Figure 1. In fact, the development of the surface of sponsored green roofs is presented in combination with the total surface of green roofs. For the same time period, Figure 2 illustrates the distribution of the installed green roofs (Maurer, 2006).
Figure 1: Development of the surface (in m2) of the green roofs in city of Linz over the period 1989-2005 (Maurer, 2006).
Figure 2: Distribution of the installed green roofs in city of Linz over the period 1989-2005 (Maurer, 2006)
[1] Exceptions: i. where the building has at least 60% green space within its plan, ii. roofs with a pitch > 20 degrees