Optimising intensive green roof environmental performance towards carbon sequestration rate

Abstract

Despite the abundant studies on the environmental performance of green roofs, studies related to carbon sequestration have received less attention from researchers. Previous studies have revealed that carbon sequestration contribution is limited compared to the amount of CO2 emitted by buildings. Furthermore, no research has been done to investigate the ways to improve carbon sequestration performance through intensive green roofs, which is crucial to offset CO2 emission. To address this gap, this research was undertaken with four research objectives which are to identify the factors affecting carbon sequestration on intensive green roofs, to investigate the current intensive green roof practice on carbon sequestration performance, to estimate the amount of carbon sequestration on intensive green roofs, and to determine the significant factors for improving carbon sequestration performance on intensive green roofs. The research objectives were achieved through 3 phases. Phase 1 was conducted through an extensive literature review and verification by experts to achieve the first objective. 20 sub-factors affecting carbon sequestration on intensive green roofs were identified and classified into 3 main factors, namely plants, the physical of green roofs, and maintenance. Phase 2 included an investigation involving nine (9) case studies with multisource evidence such as field surveys, semi-structured interviews, document reviews, and observations to achieve the second and third objectives. The investigation disclosed the current practice of intensive green roofs with three different typologies termed as Type A, Type B, and Type C. Based on the ranked factors and the rate of carbon sequestration, Type B is the best for optimising carbon sequestration performance. Overall, the nine case studies contributed to 3,601 tree planting and the average number of trees for each case study was 400 with an average density of 0.126 per tree per square metre of green roofs, while 39% of the tree species were made up of Syzygium oleina. Meanwhile, the total estimated amount of carbon sequestration for all case studies is 48,410 kg CO2 per year with an average of 5378.90 kg CO2 per year for each case study. Each tree was also estimated to sequester carbon at 11.72 kg CO2 per year. The estimated amount of carbon sequestration for one square metre of intensive green roof was 1.69 kg CO2 per year with the highest amount estimated at 7.305 kg CO2 per year. The final phase of the study achieved the fourth objective by which the data collected from the case studies were analysed using regression analysis. The analysis revealed two significant factors affecting the carbon sequestration performance of intensive green roof which are green area percentage and plant diversity. The findings provided useful guidance to policymakers, designers, facility managers, and building owners to maximise carbon sequestration on intensive green roofs to reduce global warming.