Substrate and drainage system selection and slope stabilization in an intensive-type roof garden park: case study of Athens Concert Hall

The development of the green roof market in Greece and other Mediterranean countries in general has not been standardized, unlike in Germany and other northern European countries. The construction of successful sustainable green roofs relies mainly on the development and combination of integrated systems that include green roof stabilization and the appropriate selection of a substrate and drainage system to support sustainable plant growth. The current study provides a thorough review of the decision-making process associated with the selection of substrate, drainage, and slope-reinforcing materials for the Athens Concert Hall green roof park (2 ha). For the scope of this study, guidelines from different scientific fields were modified and combined to accommodate the specifics of this project and the Hellenic climatic conditions. The challenges addressed included a roof shell with 70 different inclinations, underground retaining walls and steps, and steep slopes that reached 70 % gradients. Selection of the appropriate materials and methodologies was supported by analyses that included granulometry, bulk density, hydraulic conductivity, moisture potential curves, organic matter content, and weight at saturation and field capacity. The drainage layer consisted of a bilayered system of pea gravel and sand combined with geotextiles. Substrate characteristics were defined by the analyses undertaken and adapted to the Hellenic climatic conditions. Geogrids and honeycomb geocells were utilized separately or in conjunction on inclined surfaces. Substrate moisture measurements performed at 150 locations on the green roof revealed increased moisture fluctuations (10–35 % v/v), which were mainly caused by the presence of the underground retaining walls.