Evaluating Plant Species Suitability for a Substrate-Free Tropical Green Roof

Abstract

Greenroofs reduce building exterior-interior thermal flux and mitigate high internal air temperatures, especially in tropical climates. Tropical greenroofs are given little attention and their use remains restricted to a very low percentage of roofs due to high costs compared to traditional roofs, weight overload (mainly due to the chosen substrate) and potential waterproofing problems. We here present an alternative greenroof technique based on a reduction of the current Modern Extensive Greenroof (MEG) technique to half of its original layers. The feasibility of superficially rooting plant species from extreme habitats was tested in full scale on a single family house over three consecutive years. The innovative horticultural system is based on a substrate-free method, which has several advantages over traditional systems, including easier maintenance and minimal total weight. The reduced layout also lowers material and labor costs, facilitating widespread retrofitting of installations, mainly on low income houses in urban areas of developing countries. From a sparse initial planting, total coverage was attained in two years and 218 taxa, belonging to 20 families and various growth types, were successfully grown on the new greenroof system. Species were able to survive and grow even though signs of dynamic photoinhibition were detected. The viability of the plant assemblage together with the ability to store water due to a high degree of succulence among species indicates a broad potential for research into the use of cultivated epiphytic, lithophytic and psammophilous flora for the installation of tropical greenroofs.