Design and development of a green roof substrate for the tropics

Abstract

Green roofs can be used as an effective climate change adaptation tool in South Asia. However, there is limited information on the type of substrate and the substrate depth best suited for extensive green roofs in this tropical climate. In this research, sixteen potential substrate mixtures were prepared using locally available materials and waste materials. The properties of these substrate mixtures were tested under laboratory and field conditions to identify the substrate mix best applicable for extensive green roofs for the tropical climate of Sri Lanka. Based on the results obtained from laboratory testing it was observed that substrate mixtures that contained coir and crushed recycled bricks displayed the properties most suited for a substrate in the tropical climate. Three different substrate depths (2.5cm, 5.0cm and 7.5cm) were also tested, in order to study their suitability for adequate plant development under tropical conditions. It was observed that the 2.5cm substrate depth had successful plant establishment and adequate plant coverage. Moreover, the 2.5cm depth substrate could be easily supported on an existing roof with little/no modifications. Therefore, for the tropical climate of Sri Lanka, a 2.5cm depth substrate composed of 10% compost, 5% coir, 5% rice husk, 40% sand and 40% crushed recycled bricks is recommended.