Assessing the Impact of Green Roofing on Urban Building Energy Efficiency

Thesis Abstract

Urban areas are experiencing escalating energy demands driven by climate change, rapid urbanization, and the need for sustainable development, necessitating innovative strategies to enhance building energy efficiency. Green roofing, a sustainable building technology involving the installation of vegetative layers on rooftops, has emerged as a promising approach to mitigate urban heat island effects and reduce energy consumption. However, empirical evidence quantifying its impact on energy efficiency, particularly within diverse urban contexts, remains limited. This study aims to assess the effect of green roofs on building energy performance in a metropolitan setting, specifically focusing on residential and commercial buildings within the city of Riverside, with a population of approximately 1.2 million inhabitants and over 15,000 registered buildings. The primary objectives are to quantify the reduction in cooling and heating energy consumption attributable to green roofing, identify structural and environmental factors influencing performance, and evaluate occupants' thermal comfort and satisfaction. The research adopts a mixed-methods approach to capture both quantitative energy data and qualitative perceptions, employing a comparative case study design. The quantitative component involves selecting a sample of 40 buildings—20 with green roofs and 20 without—matched based on building age, size, and function, through stratified random sampling. Data collection instruments comprise smart energy meters, temperature and humidity sensors, and occupant surveys administered over a 12-month period to account for seasonal variations. Qualitative data are gathered through semi-structured interviews with building managers and occupants to explore perceived benefits and challenges. Data analysis employs multiple linear regression analysis to examine the relationship between green roofing and energy consumption, controlling for confounding variables such as insulation and ventilation. An ANOVA test compares energy savings across different building types and environmental conditions. Thematic analysis of interview transcripts provides insight into occupant experiences, while a combined analytical framework evaluates the consistency of quantitative and qualitative findings. The study expects to demonstrate statistically significant reductions in cooling energy usage—estimated at an average of 25%—and moderate reductions in heating load, with overall improvements in indoor thermal comfort and occupant satisfaction. These findings are anticipated to fill critical gaps in empirical data regarding sustainable roofing solutions' efficacy within urban environments. The research contributes to the existing body of knowledge by providing comprehensive, context-specific evidence on green roofs' impact on energy efficiency and occupant well-being, informing policy and sustainable building design practices. The main conclusion underscores the viability of green roofing as an effective urban heat mitigation and energy conservation strategy. Based on the findings, recommendations include integrating green roofing into urban planning policies, promoting incentives for retrofitting existing buildings, and encouraging further research into long-term performance and ecological benefits. Future studies should explore the lifecycle costs and broader environmental impacts of extensive green roof deployment across different climatic zones, extending the understanding and applicability of sustainable roofing technologies within urban ecosystems.