Effect of orientation on the water balance of greenroofs

Abstract

Green roofs are increasingly getting attention due to their water retaining capacity. An overview of the Western-European research of the last decade demonstrates there has been extensive research but it is not possible to build a complete empirical model from the available data. The only formula that can be made is valid on a yearly time scale for non-sloping roofs. An example using this formula is given for several roof types and amounts of substrate. Since an empirical approach cannot give the required results a physically based model is needed. The outlines for such a model and the influence of the slope on the different processes are given. In order to validate the theoretical parts of the model and to make empirical models of certain processes an experimental set-up has been constructed. This set-up consists of 78 lysimeters that have different slope angles, orientations and types of greenroofs. Experimental measurements, which were made during 4 periods from July to October, show that the evaporation is strongly influenced by the slope orientation, that this effect is different for the different periods and for the days within a period.