Cooling Effects of Roof Greenings at Residential Buildings—Consideration of a Hydraulic Connection to the Interior

Within the scope of this article is the presentation of a modelling and measurement approach for the effects of roof greenings and the application of the approach to evaluate the influence of roof greenings upon the thermal conditions inside a typical residential building. It is shown that overheating in summer can be reduced, and thermal comfort for inhabitants can be increased. The cooling is caused by the transpiration of plants and by the evaporation of water from the substrate. Other relevant physical effects are the shading of plants and the increase in the heat capacity of the building. In state-of-the-art buildings, a layer with a high insulating effect is incorporated into the envelope. This leads to the effect that a huge fraction of the cooling power is taken from the outside of the building and only a smaller part is taken from the inside. In order to mitigate this decoupling, a hydraulic connection between the greening and the interior of the building is introduced. To evaluate the effect of the inside cooling, the difference in the number of yearly hours with overheating in residential buildings is estimated. In addition, the reduction in energy demand for the climatisation of a typical residential building is calculated. The used methods are as follows: (1) Performance of laboratory and free field measurements. (2) Simulation of a typical residential building, using a validated approach. In summary, it can be said that green roofs, in particular with hydraulic connections, can significantly increase the interior thermal comfort and potentially reduce the energy required for air conditioning.