Concept and characterisation of green roofs and living facades built with structured systems using expanded natural cork
The increasing expansion of cities and clustering of buildings made of hard, non-porous and non-natural materials, with the consequent soil sealing and reduction of green areas, have several harmful effects on nature, the water cycle and city dwellers. Altering the built surface can mitigate some of these problems and promote a better environmental integration of buildings and the rational use of resources, including water and energy.
Green roofs and living facades (GRLF) have the desirable potential to prevent this environmental burden, including the mitigation of floods, and help to give cities the quality offered by natural landscape. Several European cities are promoting their adoption by incentive programs or making them mandatory by legislation. Additionally, the promotion of a more resource efficient and greener economy and the reduction of energy consumption are among the priorities defined in the Europe 2020 Strategy. Moreover, the possibility of incorporating different types of waste, by-products and natural derived products in construction solutions is relevant to achieving a more sustainable construction and use of buildings throughout their life cycle.
The engineering of green roofs and living facades offer extensive, healthy benefits to cities and buildings. The natural elements used in them can lessen the urban heat island effect, capture airborne pollutants and improve air quality. They can also reduce noise levels, delay stormwater runoff, thus reducing the risk of flash floods, and decrease the amount of energy needed for cooling or heating through the better insulation of buildings. However, current systems still make use of various synthetic components, and the natural elements, which offer so much welfare, are used only on the surface of the system in the form of vegetation and, occasionally, substrate. We are positive that this ecosystem can be extended through the core layers of the system, like vegetation support layer, water filter layer and drainage course with the appropriate natural material creating a healthy green roof or living facade. Expanded cork agglomerate (ICB), produced from cork waste (Portugal is the world’s largest cork producer) is suitable for building insulation and can be a good compromise between thermal insulation, environmental impact and natural integration.
This project concerns the conception and behaviour of green roofs and living facades made of healthy engineered expanded cork systems, a totally natural and environmentally friendly product, as the inner layer of the system. It plans to use one or more layers of expanded cork as a lightweight water retention layer, a drainage layer, and simultaneously as insulation. This system should provide the required thermal insulation and durability, protect against the filling of drainage layer and also guarantee that the pH of the substrate stays between 6.0 and 8.0. The system is also expected to be light enough to extend its applicability to retrofitting existing buildings with structural limitations.
The project has an experimental and a numerical goal. Experimentally, the GRLF solution will be studied using bioclimate chambers, separated from one another by the green roof or living facade. Here, vegetation growth, rainfall, solar radiation, wind, thickness of the rooting layer will be induced and monitored. This is a new approach. The experimental programme will also involve the characterisation of the material and specify the hydraulic permeability, water retention capacity, thermal conductivity and specific heat for different expanded cork densities with variable water column and material water content. The viability of combining green roofs with rainwater harvesting systems will also be analysed by determining expressions for run-off coefficients and by the physical-chemical analysis of the effluent, in view of its use in various non-potable purposes in the building.
Finally, numerical techniques will be developed to model the hydraulic flow and hygrothermal and acoustic behaviour of this multi-layered system throughout the year and its experimental validation. The development and optimisation of this innovative ecological solution requires both an appropriate experimental material characterisation and the existence of appropriate modelling tools.
As output of the project, it is expected to: