Assessing the Impact of Green Roofs on Urban Building Energy Performance

Thesis Abstract

Urban areas are increasingly adopting green roofs as a sustainable measure to mitigate the environmental impacts of dense building developments and to improve urban thermal comfort. However, empirical evidence on the extent to which green roofs influence building energy performance remains limited and context-specific. This study aims to assess the impact of green roofs on the energy efficiency of urban buildings, with a focus on quantifying cooling and heating energy savings attributable to their implementation. The specific objectives include analyzing the thermal performance of buildings with green roofs compared to conventional roofs, evaluating the variations across different building typologies, and identifying the key factors influencing energy savings in green roof systems. The research adopts a comparative case study design, with a mixed-methods approach integrating quantitative energy data collection and qualitative interviews. The population comprises 60 commercial and residential buildings in a temperate climate zone with installed green roofs, selected through stratified random sampling to ensure representation across building types and sizes. Data collection instruments include smart energy meters for continuous energy consumption monitoring over a 12-month period, thermal imaging cameras to assess roof surface temperatures, and semi-structured interviews with building managers and occupants to contextualize technical data. Data reliability is ensured through calibration of instruments and inter-rater reliability checks for interview coding, while validity is maintained through triangulation of multiple data sources. Analytical techniques involve descriptive statistics to summarize energy consumption patterns, paired t-tests to compare energy use before and after green roof installation, and multiple regression analysis to identify predictors of energy savings, controlling for external climate variables. Additionally, thematic analysis is employed to interpret qualitative data, providing insights into occupant perceptions and maintenance considerations. The study tests hypotheses aligned with the theories of the Urban Heat Island mitigation and the Building Physics Framework, which underscore the thermal and energy performance impacts of green roofs. It is expected that the results will demonstrate statistically significant reductions in cooling energy demand, particularly during peak summer months, with variable energy savings observed across different building types and green roof configurations. The findings are anticipated to show that green roofs can contribute to a reduction of up to 30% in cooling energy consumption, with moderate effects on heating loads. Key factors influencing these savings include roof insulation quality, green roof depth and vegetation type, and building orientation. This research contributes to the existing body of knowledge by providing empirically derived, context-specific data on the energy performance benefits of green roofs, addressing gaps related to climate variability and building typology influences. The study offers a validated framework for assessing green roof effectiveness, which can inform policy and sustainable urban planning strategies. The main conclusion affirms that green roofs are a viable strategy for enhancing urban building energy efficiency, especially when integrated with complementary passive design features. Recommendations include promoting wider adoption of green roofs in urban planning, optimizing design parameters for maximum energy savings, and encouraging further longitudinal research to evaluate long-term performance and maintenance impacts. Future studies should explore the life cycle cost-benefit analysis of green roof systems and their adaptability to different climatic regions, ensuring comprehensive sustainability assessments.