Cost–carbon trade-offs in green infrastructure: a case of Nigeria

Purpose This study aims to address the lack of a structured framework for understanding how stakeholders in developing countries, particularly Nigeria, balance construction cost constraints with sustainability objectives in green infrastructure projects. This gap is intensified by limited green financing, unstable market and decision-making approaches that overlook both economic and qualitative sustainability factors. To address this, the study proposes a consensus-based method for assessing cost−carbon trade-offs and identifying key drivers that align cost control with improved sustainability outcomes. Design/methodology/approach A qualitative, three-round Delphi study was conducted with 20 purposively selected experts, including public clients/regulators, consultants, contractors, financiers, suppliers and academics. The first round involved a focus group discussion to generate initial themes, while the second and third rounds used content-validated questionnaires refined from Round 1. The reliability of the items was assessed using Cronbach’s alpha (threshold = 0.70), and consensus was measured with Kendall’s coefficient of concordance (W), which increased across rounds, indicating convergence. Findings Four interlocking themes were identified as critical to cost–carbon decision-making in Nigerian green infrastructure delivery: perceived value of sustainability; cost-sustainability strategies; institutional and regulatory levers; and knowledge and capacity development. These insights were synthesized into an integrative framework emphasizing evidence-based persuasion, strategic collaboration, supportive regulation and capacity development. Originality/value This study is novel in presenting a framework for cost–carbon decision-making in green infrastructure projects. It advances construction management knowledge by revealing how cognitive, institutional, strategic and human-capability factors interact to achieve sustainable project outcomes, thereby offering both theoretical and practical significance.