Multi-sectoral efforts are required for decarbonising the building sector: a case in Hong Kong

The study addresses how to achieve deep decarbonisation of the building sector—a major emitter responsible for about 39% of global CO2—within the constraints of Paris Agreement 1.5 °C targets and regional carbon neutrality visions. As a typical end-use sector, buildings depend on multiple upstream and parallel sectors (electricity supply, manufacturing of materials, and transportation), so mitigation outcomes hinge on cross-sector dynamics rather than isolated building-only actions. Existing studies often evaluate single measures or treat other sectors with simplified assumptions, obscuring interconnections across building life-cycle stages and contributing sectors. The research proposes a comprehensive “stage-sector-measure” framework to clarify these interdependencies, quantify mitigation mechanisms across a building’s life cycle, and develop a multi-sector decarbonisation roadmap, using Hong Kong as a high-rise, high-density case city.

Prior work has explored building-sector decarbonisation using top-down regressions and system dynamics to forecast impacts of socio-economic drivers and energy efficiency, and via life cycle assessment (LCA) focusing on specific stages or technologies. Examples include machine learning-based forecasts for Hong Kong’s building carbon footprint emphasizing electricity efficiency and clean power; comparative analyses of technical pathways in different cities; and system dynamics for city-scale building emissions under varying efficiencies. LCA studies have examined embodied (materials) and operational stages as well as waste management, but common gaps remain: (1) fragmented focus on individual sectors or measures rather than whole life-cycle coverage; and (2) unclear mechanisms linking multi-sector measures to different building stages and their interactions. These shortcomings limit comprehensive strategy design. The present study responds by integrating process-based LCA with bottom-up modeling to connect life-cycle stages, contributing sectors, and detailed measures within a unified evaluation framework.

The study develops an integrated process-based LCA and bottom-up modeling framework termed “stage-sector-measure.” It decomposes the building sector into six life-cycle stages: (1) material production, (2) material transportation, (3) construction, (4) operation, (5) demolition, and (6) waste transportation and disposal. Four contributing sectors—manufacturing, transportation, building, and electricity—are linked to each stage through key factors. A catalog of 23 measures in six types is identified: cleaner production of building materials; phase-out of diesel goods vehicles; construction method innovation (prefabrication); building energy efficiency; building electrification; and clean electricity (alternative fuel mix and CCS). Two-step calculation: (i) quantify how changes in key factors (e.g., material emission factors, vehicle fuel shares, construction/operation fuel mixes, electricity emission factors) affect stage-wise emissions; (ii) quantify how measures alter these factors. The approach provides compound mitigation effects and captures interactions. Formalization: The paper presents equations for mitigation potentials per stage. For example, in material production, mitigation arises from lower material emission factors (manufacturing) and reduced material demand via lower waste ratios from prefabrication (building). Material transportation depends on vehicle fuel shares (transport), material quantities and waste ratios (building), transport distances, and electricity emission factors (electricity). Construction emissions reflect construction mode (affecting diesel/electricity use) and electricity emission factors. Operation depends on building fuel mix (electricity vs LPG/coal) and end-use energy efficiency as well as electricity emission factors. Demolition and waste transport mirror the above dependencies, with landfill disposal assumed to have no direct emissions. Equations (1)–(25) detail these relationships, including factor changes (ΔEC by fuel), emission factors EF, energy generation mix EGR, CCS removal rate RR, and measure penetration PR. Scenario design and projections (Hong Kong, 2020–2050):

• Building scale: Floor areas of residential, commercial, and industrial stocks and flows (new and demolished) are projected via per-capita area methods and policy plans; stocks generally rise to 2050, new-build flow declines with slower population growth.
• Measures and parameterization: • Cleaner production: Eight key materials (aluminium, brick, cement, ceramic, concrete, glass, steel, timber) adopt cleaner production trajectories (largely influenced by Mainland China production), reducing material emission factors. • Phase-out of diesel goods vehicles: Progressive shift to electric and hydrogen goods vehicles, with all diesel phased out before 2040; by 2050, 60% electric and 40% hydrogen. • Construction method innovation: Prefabrication share rises from ~20% (2020) to 70% (2050), lowering material waste and construction-stage diesel use. • Building energy efficiency: End-use energy intensity reductions for nine end-uses (e.g., air conditioning, lighting, refrigeration) at annual rates from 0.4% to 1.2%, applied across residential, commercial, and industrial buildings. • Building electrification: Increasing electricity share in building operations; coal phased out by 2025; LPG share declines; electricity shares rise to 85.4% (residential), 92.8% (commercial), 93.0% (industrial) by 2050. • Clean electricity: Alternative generation mix (coal eliminated before 2030; gradual growth of WtE, solar, offshore wind to 10% by 2050) and rising imports from Mainland China (28% in 2020 to 50% in 2050). CCS deployment in two steps (2030 and 2040) on thermal generation with 90–95% capture. Sensitivity analysis: Elasticity coefficients quantify output sensitivity to parameter changes. The carbon removal rate by CCS (ELA ≈ 2.761) is most sensitive; floor area of building stocks (0.886) and electricity emission factors (0.602) are also influential. Other parameters (transport distances, vehicle energy intensities) show much lower sensitivity.

• Overall decarbonisation: Under business-as-usual, building-sector emissions rise from 27.0 Mt (2020) to 32.2 Mt (2050). With measures, emissions fall to 4.2 Mt in 2050, an 84.4% reduction relative to BAU 2050, enabling near-neutrality by 2050 with offsets.
• Temporal dynamics: Largest decade-scale mitigation occurs in 2020–2030 (13.9 Mt) and 2030–2040 (12.0 Mt), with smaller gains 2040–2050 (2.1 Mt). Sharp drops occur around 2030 and 2040 with staged CCS deployment.
• Stage-wise outcomes (2050 vs 2020): Remaining shares range from 5.6% (material transportation) to 28.4% (demolition). Material and waste transport stages are largely abated due to zero tailpipe emissions from goods vehicles; construction and demolition retain 26.1% and 28.9% of 2020 emissions given sustained activity levels.
• Sectoral contributions: Electricity sector dominates mitigation with 11.6 Mt (2020–2030), 20.6 Mt (2030–2040), and 20.1 Mt (2040–2050). Building-sector measures are second-largest; transportation mitigation is negative before 2040 because electricity has high emission factors until power decarbonises.
• Measure contributions (cumulative): Clean electricity supplies 71.8% of total mitigation; building energy efficiency contributes 20.6%; cleaner production of building materials adds 4.5%. Phase-out of diesel goods vehicles and building electrification show limited or negative short-term effects but become positive as electricity decarbonises.
• Within-stage measure impacts: • Material production: Cleaner production of concrete (32.9%) and steel (30.0%) are the largest contributors, jointly 62.9% of stage mitigation. • Other stages: Alternative electricity fuel mix and CCS together deliver 80.1% (material transport), 42.7% (construction), 66.0% (operation), 82.2% (demolition), and 81.7% (waste transport and disposal) of mitigation.
• End-use efficiency: Air conditioning efficiency yields 2.66 Mt of mitigation (46.1% of operation-stage efficiency gains), exceeding its 25–34% consumption share; other end-uses each contribute 0.16–0.70 Mt.
• Interactions: Electrification of buildings and goods vehicles can increase emissions initially due to carbon-intensive electricity, but becomes strongly beneficial after power decarbonisation, highlighting cross-measure interactions.

The findings substantiate the central hypothesis that multi-sectoral, life-cycle strategies are essential for deep decarbonisation of the building sector. By explicitly linking stages, sectors, and measures, the framework clarifies mechanisms and interactions often obscured in single-sector analyses. Results show electricity system decarbonisation is the primary lever (>70% of total mitigation), while manufacturing-sector cleaner production is pivotal for embodied emissions, and building energy efficiency is critical in operations. Negative short-term impacts from transport and building electrification underscore the need for coordinated sequencing with power decarbonisation. The approach is generalisable to other cities, provided localised data and policy trajectories, and it informs policy design: economic incentives (subsidies, feed-in tariffs, and carbon pricing/trading) can accelerate clean electricity and CCS deployment; public awareness and behaviour-change campaigns are essential for widespread building efficiency adoption. Sensitivity analysis underscores the importance of CCS performance and electricity emission factors, suggesting robust planning and contingency strategies around these parameters.

This study introduces a stage-sector-measure framework that integrates process-based LCA with bottom-up modeling to quantify multi-sector mitigation across the full building life cycle. Applied to Hong Kong (2020–2050), the roadmap indicates an 84.4% reduction in building-sector emissions by 2050, dominated by clean electricity (alternative fuel mixes and CCS), complemented by building energy efficiency and cleaner material production. The framework illuminates interdependencies and sequencing across measures and sectors, offering a replicable template for urban building decarbonisation. Future research should (1) refine behavioral, design, and appliance-level determinants of operational energy efficiency; (2) incorporate rigorous techno-economic and cost-effectiveness analyses to guide prioritisation; and (3) expand system boundaries to additional sectors and emerging measures (e.g., AI-enabled energy management) as urban systems evolve.

• Measure adoption trajectories rely on policy targets and reports with simplified assumptions (e.g., fixed annual efficiency improvements by end-use), omitting detailed behavioral, design, and appliance heterogeneity.
• Lack of explicit techno-economic analysis; costs and benefits that shape feasibility and prioritisation are not quantified (e.g., higher LCOE for renewables and CCS costs).
• System boundary excludes potential future contributors (e.g., broader service-sector dynamics, advanced digital management systems), possibly underestimating or misallocating mitigation potential.
• Some parameters (e.g., electricity emission factors, CCS removal rates) drive high sensitivity; deviations from assumed values could materially alter outcomes.