Panelised offsite construction supply chains in New Zealand residential sector : an integrated system dynamics and multi-objective optimisation framework : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Construction, School of Built Environment, College of Science, Massey University, Auckland, New Zealand

Abstract

The New Zealand residential construction sector faces persistent capacity and productivity constraints, necessitating the adoption of practical solutions to meet growing housing demand. Offsite Construction (OSC) presents considerable potential to address residential delivery challenges; however, it has not yet been widely adopted within New Zealand. Therefore, their full potential for integration and widespread adoption remains unrealised. OSC performance is fundamentally shaped by Supply Chain Management (SCM) effectiveness, where Offsite Construction-Supply Chain Management (OSC-SCM) performance can be systematically measured through operational efficiency and the ability to withstand and resolve supply chain related challenges. There is a lack of an integrated and dynamic framework that explicitly models and optimises panelised OSC-SCM performance by capturing the impact of supply chain barriers on cost, time, and material waste. To increase OSC acceptance and performance, this study assesses and examines the significance of aligning OSC procedures with SCM. To unlock the full benefits of offsite methods, organisations must prioritise aligning OSC strategies with robust supply chain management (SCM) practices, thereby improving operational efficiency and overcoming the challenges constraining their broader adoption. A deeper investigation into this matter, along with the underlying factors influencing OSC’s performance, is therefore critical. Building on the findings of the literature review, this study develops a comprehensive framework for panelised OSC-SCM to enable a more rigorous examination of the critical factors impacting this effective integration. By addressing both project-level performance outcomes and higher-level management alignment, the research seeks to identify the underlying mechanisms through which these barriers contribute to the underperformance of residential OSC projects. The empirical findings from semi-structured interviews with key stakeholders highlighted several critical barriers to OSC adoption in New Zealand (NZ), including labour shortages, design modifications, crane and transport limitations, and weather-induced delays. To strengthen the credibility of these qualitative insights, a triangulation approach was employed, whereby interview evidence was systematically compared with system dynamics modelling outputs. This methodological integration revealed strong alignment between perceived and simulated disruptions, confirming that small but recurring schedule interruptions can escalate into significant project-level overruns through feedback loops. The system dynamics model further illuminated the complex interdependencies across cost, time, and material waste, demonstrating how isolated inefficiencies within the OSC supply chain can trigger cumulative and non-linear effects on residential project performance.

This research proposes strategies for optimising panelised OSC–SCM and offers actionable guidance for construction firms and policymakers seeking to enhance capability, capacity, and overall performance in the residential sector. This study emphasises the material dimension of OSC, specifically the use of engineered panelised systems, alongside supply chain and project management factors. Depending on the system's design and use, each material makes a distinct contribution to improving OSC performance, whether through lower embodied impacts, greater precision, or reduced waste. The OSC-SCM framework's integration of sustainable material choices aligns construction performance objectives with broader environmental goals, positioning OSC as a key pathway for delivering low-carbon housing in NZ and internationally. In line with the boundary of this thesis, the environmental performance is considered as an embedded supply-chain outcome of OSC-SCM, focusing on embodied impacts rather than operational energy performance. This study emphasises how supply chain optimisation and the adoption of sustainable materials can work together to decarbonise the housing sector by integrating material choices within the OSC-SCM framework.

The study identifies and critically analyses the factors most influential in shaping OSC adoption and integration, considering not only its role within the housing industry but also its underlying operational processes and the decision-making resources required for effective implementation. Building on these insights, the multi-objective optimisation models created with the Genetic Algorithm (GA) and the Grey Wolf Optimisation (GWO) included the validated barriers. To identify feasible options under the stochastic conditions of OSC supply chains, each algorithm facilitated the investigation of trade-offs among time, cost, and material waste reduction. Together, the optimisation results provide a rigorous quantitative foundation for decision support, enabling practitioners to identify high-impact constraints, evaluate trade offs, and configure supply chains more effectively.

The findings demonstrate how an optimal supply chain configuration can be achieved by systematically incorporating multiple schedule variabilities, thereby reflecting the stochastic realities of panelised OSC projects. Beyond improving predictive accuracy, the proposed model constitutes a foundational framework for a decision-support system specifically tailored to practitioners operating in OSC-SCM. Its application enables the quantitative identification and prioritisation of critical factors driving variations in both schedule and budget, providing a transparent mechanism for risk-informed decision-making. The robustness of the framework was confirmed through rigorous quantitative validation, which illustrates its capacity to address the inherent complexity and uncertainty of supply chain scheduling in residential construction. These results underscore not only the model’s practical utility for enhancing project-level performance and achieving measurable cost efficiencies but also its broader potential to inform strategic supply chain management practices and policy frameworks that support the scaling of OSC adoption in New Zealand’s housing sector. These findings are equally applicable to international construction markets dealing with comparable issues.