ORGANISING LARGE SCALE GREEN COVERED ROOFS, Classification of green roof specifications and green roofs implementation; the economics of green roofs

misbe2011 Tracking Number 54

During the last two decades the use of plants on rooftops has grown fast. Cities use different arguments to make policies for large-scale programs possible. One argument is that green covered roofs contribute to reduction of CO2 emissions on the local scale of the building, which is mitigation. CO2 reduction can be realised because there is a contribution to extending the life expectancy of the roof. There is a potential reduction in fossil energy use, especially in cooling. On this scale water can be retained and PM can be captured, which are adaptation approaches. When roofs are covered with plants on a large scale this will also contribute to adaptation, often being part of sustainable water management. However there is an intriguing difficulty in organising the intertwining of these two approaches to climate, energy and water: It is very hard to organise, since the stakeholders keep their natural roles in their traditional organisational patterns. They are not accustomed to collaboration in this new context. New patters and new collaborations however have to be established soon to speed up the process. The paper will show the arguments for mitigation and adaptation approaches on the scale of buildings and on scale of cities. These arguments are elaborated against the background of cost and benefits from the major stakeholders. Calculations of municipalities showed that benefits for private partners, investing in green roofs, are smaller compared to the public benefits on a larger scale. The total private benefit can even be negative. Nevertheless the summation of private and public benefits is nearly always positive. The calculations also show that the total benefits are the largest in the high-density areas surrounding the city centre and lowest in industrial areas. The city centre itself is most beneficial for public benefits. The paper summarises the arguments of cities, as part of their policy and put them opposite of the arguments of urban designers in order to distinguish gaps between intentions of policy makers and design criteria of urban planners, which led to recommendations for both. Then an analysis shows the potential for successful collaboration as well as possible risks. The decision makers, more specified the public sector, seems to have the key to the breakthrough. They have the largest financial benefits to get the right roofs on the right places. Acquire knowledge, sharing knowledge (and experiences) and moreover the inevitable change in the way one collaborates with the partners is the first step to make. From the construction contractors perspective it is important that their product will fit the private investors needs as well as the public subsidies interests and still make a profit. They will serve the market, but who will direct the market? The paper will conclude with recommendations for improvements in collaboration to speed up the realisation of green covered roofs on large scale. Keywords: Green Covered Roofs, Design and Construction Process, Sustainable Water Management, Green Urban Policy, Cost benefit.