Comparative Life-Cycle Energy Use in High-Rise vs. Low-Rise Buildings

Thesis Abstract

This study addresses the escalating energy demands of urban forms by comparing life-cycle energy use between high-rise and low-rise buildings, highlighting gaps in conventional design practices that prioritize operational energy savings while underrepresenting embodied energy and end-of-life impacts. The aim is to quantify and contrast cradle-to-grave energy consumption across construction, operation, and demolition phases for representative high-rise and low-rise residential and commercial buildings, and to identify design, material, and operational factors driving differences. Specific objectives include (1) determining the life-cycle energy intensity (MJ/m2) for each building category; (2) partitioning energy use into embodied, operational, and end-of-life components; (3) evaluating the influence of climatic zones, building envelope performance, and vertical transportation on life-cycle energy; (4) assessing the sensitivity of results to material choices and occupancy patterns; and (5) deriving practical recommendations for minimizing life-cycle energy through integrated design strategies. The methodology employs a comparative, cross-sectional research design using a mixed-methods framework. The population comprises contemporary urban buildings in three climate regions with matched floor area and service levels high-rise (20–40 stories) and low-rise (2–4 stories) structures. A purposive sample of 12 buildings (6 high-rise, 6 low-rise) is selected to reflect representative typologies and material assemblies. Data collection instruments include (i) a Bill of Quantities and architectural drawings for embodied energy estimation, (ii) detailed energy models calibrated with measured utility data over a 24-month period, (iii) questionnaires and interview guides for facility managers to capture occupancy schedules and maintenance regimes, and (iv) life-cycle inventory data from established databases (e.g., ecoinvent, nationally published benchmarks). Embodied energy is estimated using input-output and process-based life-cycle assessment methods, while operational energy is derived from monitored energy consumption normalized by floor area and occupancy. End-of-life energy uses are projected based on deconstruction pathways and recycling rates. Validity and reliability are ensured through triangulation of theoretical models, cross-validation with metered data, and test-retest of survey instruments. Analytical techniques include descriptive statistics to summarize energy components, and inferential analyses comprising multivariate regression to identify determinants of life-cycle energy, ANOVA to test differences between high-rise and low-rise categories, and sensitivity analysis to examine parameter uncertainty. A combined life-cycle energy model is specified to estimate cradle-to-grave energy per square meter, incorporating factors such as envelope U-values, glazing ratios, insulation thickness, mechanical system efficiency, elevator performance, and occupancy patterns. The study also employs a simple scenario analysis to explore low-energy retrofit options and their impact on life-cycle energy. Theoretical grounding draws on the Theory of Planned Behavior to interpret occupancy-related energy use behavior and on the Theory of Embodied Energy to frame material and construction choices; a conceptual framework links building typology, climatic context, and life-cycle phases to energy outcomes. Expected findings suggest that embodied energy constitutes a substantial share of total life-cycle energy in high-rise developments due to material intensity and long supply chains, while operational energy differences are moderated by vertical transportation efficiency and pace of occupancy. Low-rise buildings may exhibit lower embodied energy but potentially higher operational energy per unit floor area depending on envelope performance and fenestration strategies. The research anticipates that climate-specific factors and high-performance envelopes can mitigate life-cycle energy in both categories, with mixed-use configurations and modular construction emerging as particularly impactful. Contributions to knowledge include a rigorous comparative quantification of life-cycle energy for high-rise versus low-rise buildings, an integrated methodological framework combining cradle-to-grave LCA with monitored energy data, and evidence-based design recommendations for reducing life-cycle energy across urban forms. The study will inform policy discourse on sustainable urban density, building codes, and procurement practices by highlighting the relative importance of embodied energy and the effectiveness of envelope, material choices, and vertical transportation strategies in shaping overall energy performance. The main conclusion underscores the primacy of adopting holistic life-cycle thinking in urban building design, advocating for early-stage material optimization, low-embodied-energy supply chains, and high-performance, occupant-centered operation protocols; recommended actions include adopting integrated project delivery, enhanced data transparency for embodied energy, and policy incentives for retrofit-driven life-cycle energy reductions.