Impact of Urban Green Roofs on Building Energy Use and Thermal Comfort

Thesis Abstract

Urban environments increasingly rely on retrofit and newly installed green roofs as a strategy to mitigate energy demand and enhance occupant thermal comfort, yet empirical evidence on their effectiveness across diverse building types and climates remains fragmented. This study investigates the impact of urban green roofs on building energy use and thermal comfort, addressing the gap between theoretical benefits and realized performance in real-world settings. The aim is to quantify the energy savings attributable to green roofs and assess changes in indoor thermal conditions under varying meteorological conditions and occupancy patterns. Specific objectives include (1) to compare monthly and seasonal energy consumption for heating and cooling between green-roofed and conventional roofs in similarly configured buildings; (2) to evaluate the effect of green roofs on indoor thermal comfort indices (PMV, PPD) across different spaces and occupancy schedules; (3) to identify moderating factors such as roof depth, substrate conductivity, irrigation regime, and building envelope characteristics that influence energy performance; and (4) to develop a practical framework for predicting energy and comfort outcomes based on measurable roof and building parameters. The study adopts a comparative field design, combining quasi-experimental and observational components over a two-year period. A purposive sample of 40 office and multifamily residential buildings in a temperate urban region will be selected, comprising 20 green-roofed and 20 conventionally roofed structures with comparable floor area, age, and occupancy profiles. Data collection will integrate metered energy data (electricity for HVAC and lighting, monthly), meteorological data from a dedicated on-site weather station, interior temperature and humidity loggers (placed in representative spaces, sampling at 15-minute intervals), and occupant surveys to capture perceived thermal comfort and satisfaction. Instrument reliability and validity will be ensured through calibration procedures, pilot testing, and cross-validation with utility bills. The study will employ mixed-methods analysis quantitative analysis will include panel data regression with fixed effects to isolate roof type effects while controlling for weather, occupancy, and building characteristics; time-series decomposition to discern seasonal patterns; and multivariate regression to assess the influence of roof depth, substrate type, irrigation, and insulation on energy use and thermal indices. Thermal comfort will be analyzed using PMV/PPD models, with sensitivity analyses conducted for different metabolic rates and clothing insulation levels. A structural equation model will be specified to explore causal pathways between roof performance factors, energy consumption, and occupant comfort. Theoretical framing will integrate the Sustainable Building and Urban Ecology theories, complemented by the theory of heat transfer in porous media, and the Urban Microclimate framework to interpret local meteorological modulation by green roofs. Ethical approvals will be obtained, informed consent secured for occupant surveys, and data anonymized to protect privacy. Anticipated findings include (a) a statistically significant reduction in cooling loads during peak summer months for green-roof buildings, with more modest or negligible heating energy differences in winter; (b) improvements in interior thermal comfort during hot periods, reflected in lower PMV values and reduced PPD percentages in spaces beneath green roofs; (c) pronounced energy and comfort gains in buildings with greater roof depth and higher soil moisture retention, moderated by irrigation practices and substrate thermal properties; (d) nuanced outcomes for mid-season transitions where increased evapotranspiration may elevate latent cooling benefits but require careful irrigation management. The study will contribute to knowledge by providing granular, empirically derived estimates of energy savings and comfort enhancements attributable to green roofs, offering a transferable framework for predicting performance under varying configurations and climates. Policy relevance includes evidence to inform urban retrofit guidelines, resilience planning, and incentives for green-roof adoption. The main conclusion anticipates that well-designed green roofs yield measurable energy reductions and enhanced indoor comfort in temperate urban settings, particularly when integrated with optimized irrigation regimes, depth specifications, and targeted envelope improvements. Recommendations include standardized monitoring protocols for green-roof projects, guidance on optimal roof depth-to-weight ratios for different building archetypes, and decision-support tools that integrate climate data, building characteristics, and occupant comfort targets to forecast energy and comfort outcomes.