This paper presents methods for evaluating layout alternatives based on occupants' interactions for workplace design during the early design phase. The research proposes a modelling framework to simulate domain-specific patterns of occupancy and social interactions, as well as the process of design evaluation. The paper introduces a framework for an agent-based model using the Unity gaming engine to incorporate both architectural and non-architectural parameters derived from existing literature on organisational spatial and social behaviour. The experiments employ systematic approaches to vary design parameters and provide a comparative evaluation of layouts based on the number of face-to-face interactions. The method proposed in this paper can assist design stakeholders in creating a workplace environment for knowledge industries, where face-to-face interactions are considered sources of innovation. The presented modelling framework can also be adopted in other domains to evaluate the influence of spatial design on occupants' social interactions.