Purpose - Within construction procurement, transaction cost economics offers a mechanism to understand "unseen" costs associated with the pre- and post-contract work. Pre-contract, these include costs related to information gathering and procurement. Post-contract they include activities of contract administration and enforcement. The purpose of this paper is to estimate the magnitude of transaction costs (TCs) for different procurement systems used in construction projects in New Zealand. Specifically estimating the relative values of TCs for Traditional and Design-Build delivery systems for the purpose of comparison. Design/methodology/approach - This study develops a conceptual model for the relationship between procurement systems and TC. The model was operationalized and developed into a questionnaire. A cross-sectional sample approach was deployed, involving pilot and survey questionnaires, and results verification through "real world" cases. Data were sought from construction professionals in management, design and operations (i.e. project managers, architects, engineers, quantity surveyors, and procurement officers). TCs were measured using time-spent conducting procurement-related activities as a surrogate for cost. Professionals evaluate their time-spent in procurement activities using a Likert scale 1-5, comparing the Traditional and Design-Build delivery systems. Data were triangulated with "real world" cases to test and explain the developed model. The test included validity and reliability, path analysis, regression analysis, factor analysis, and structural equation modelling (SEM). The primary analytical technique used was SEM to yield information on goodness-of-fit, model development and comparison, and confirmatory strategies. SPSS Amos 21 statistical software was used for data analysis and model development. Findings - The results suggest that procurement systems have indirect impact on TCs. The relationship between procurement systemand TCs is fully mediated by costs of information, procurement, administration, and enforcement. Applying the developed models (the Traditional and Design-Build) to "real world" cases, it was found that TCs in the Traditional system amounts to 18.5 percent of the annual salary cost of a project manager (as an indicator quantum), while in the Design-Build system, it amounts to 14.5 percent of the annual salary cost of a project manager. TCs were calculated using regression equations based on factor loadings in the Traditional and Design-Build models. Practical implications - This study applies new theoretical model for the link between procurement system and TCs, investigating and empirically demonstrating the influence of procurement system on TCs in construction. It also offers a new plausible explanation for the factors influencing TCs in procurement. The study emphasizes "in-house" TCs from the perspective of the professionals. The findings have practical implications on construction business practice due to their robust empirical nature and theoretical framework, which might enhance the performance of the construction industry. Originality/value - This study contributes to the procurement selection in construction, by introducing a new conceptual model for the link between procurement system and TCs. It has extended the current practices for procurement selection by estimating TCs for the Traditional and Design-Build systems for comparison.