Design and Evaluation of Green Roof Systems for Urban Heat Island Mitigation

Thesis Abstract

Urban areas worldwide are experiencing rising temperatures attributable to the Urban Heat Island (UHI) effect, which exacerbates energy consumption, air pollution, and public health challenges. Green roof systems have emerged as a sustainable strategy for mitigating UHI by enhancing insulation, promoting evapotranspiration, and improving urban greening. Despite burgeoning interest, empirical evaluations of green roof designs tailored for specific climatic and urban contexts remain limited, necessitating comprehensive investigation into their optimal design and functional efficacy. The primary aim of this research is to design, implement, and evaluate green roof systems aimed at reducing urban heat, thereby contributing to sustainable urban climate adaptation strategies. Specific objectives include (1) identifying key design parameters influencing thermal performance of green roofs in temperate urban environments; (2) developing prototype green roof systems with varied substrate depths, vegetation types, and irrigation regimes; (3) measuring thermal, acoustic, and stormwater management performances through field monitoring; and (4) assessing occupants’ thermal comfort and energy savings associated with green roof adoption. Employing a mixed-methods research design, the study integrates quantitative field measurements and qualitative occupant surveys. The population comprises ten selected rooftop sites within the metropolitan core of a temperate city, with a total sample size of 50 residential and commercial buildings. A stratified random sampling technique ensures diverse representation across building typologies and rooftop conditions. Data collection instruments include digital thermometers, pyranometers, and soil moisture sensors for environmental data, alongside structured questionnaires administered to building occupants. The validity and reliability of measurement instruments are established through calibration protocols and pilot testing. Quantitative data will be analyzed using descriptive statistics, inferential techniques such as ANOVA and multiple regression to assess relationships between design variables and thermal performance, while thematic analysis will interpret qualitative data on occupant perceptions. Expected findings indicate significant correlations between substrate depth and heat flux reduction, with deeper substrates yielding greater cooling effects due to enhanced insulation and evapotranspiration. Variations in vegetation type and irrigation regimes are anticipated to influence thermal mitigation efficacy, with drought-resistant native species providing comparable benefits to more resource-intensive plants. The study also expects to demonstrate improved occupant thermal comfort and measurable reductions in cooling energy consumption in buildings equipped with optimized green roof systems. These empirical results will generate a validated conceptual model illustrating the interdependencies between green roof design parameters and thermal performance outcomes. The study's contribution to knowledge lies in providing an evidence-based framework for designing context-specific green roof systems that maximize UHI mitigation benefits while balancing resource requirements. It advances understanding of the relationships among substrate configuration, vegetation selection, and environmental performance metrics within temperate urban settings. Policy implications include guiding municipal urban greening initiatives and building codes toward incorporating effective green roof practices. The main conclusion underscores that tailored green roof designs can substantially attenuate UHI effects, promote environmental sustainability, and enhance occupant well-being. The study recommends adopting standardized design criteria based on empirical findings, incentivizing green roof integration through policy support, and conducting longitudinal assessments to evaluate long-term performance and maintenance needs. Future research avenues include exploring scalable models for diverse climatic zones and economic analyses of green roof implementation costs versus environmental and energy savings.