Analysis of physical and chemical properties of alternative substrate material for sustainable green roofs

Abstract Green roof is the roof of a building that is partially or completely enfolded with vegetation and its associated components. It promotes the sustainability of buildings and provides comfort for urban ecosystem. We have investigated the viability of using organic waste as a growing medium. This study determines the most suitable growing substrate by investigating organic wastes of Sawdust, Wood bark, Bio char, Coir, Compost and Base medium under the parameters of density, moisture content, drought resistance and thermal resistance, contribution for vegetation growth, pH, electric conductivity and nutrient constituents. Investigation of chemical parameters is a unique aspect of this study. New methodologies using mathematical concepts were used to find thermal conductivity and EC of specimens in our research. Preliminary study results shows that the most substrate composition will comprise 60% growing medium and 40% base medium (fertilizer + potting mix).During the experimental studies, we have compared the test results of each organic waste specimens under the mentioned physical and chemical parameters. Base medium (90:10) has highest bearing capacity to withstand external loads including vegetation and other imposed loads. Sawdust (60:40) exhibited optimum attributes for lightweight substrate by having least saturated unit weight, dry unit weight and the highest moisture content. In terms of drought resistance and vegetation growth, Bio char (60:40) was exceptional. Wood bark (60:40) exhibited the most convincing thermal resistance. The best characteristics in terms of pH, EC and nutrient content were exhibited by Sawdust (60:40), Coir (60:40) and Compost (60:40) correspondingly. Based on final ratings by considering all the experimental results, Coir (60:40) have emerged as the optimum growing medium in terms of physical and chemical properties. The authors emphasize to utilize this experimental study results into large-scale construction industries to promote the urban ecosystems through sustainable green roof constructions.