State-of-the-art products commonly outperform construction products that are used in day to day building practice. Also construction products appear to have a diffusion curve that differs from consumer products, slower at first, more rapid later. The social capital theory helps us to understand why certain actors are able to get their ideas adopted and why others do not. Aim of this paper is to explore to what extend social capital theory may provide explanations for the way in which innovative construction products are diffused. Therefore social capital literature and building process literature are compared. Construction process literature shows that the industry is fragmented and contacts between the various professional networks are limited to that in the building projects. Even more so the contact in construction projects appears to be short-term oriented. Social capital literature provides an explanation (network closure) for both opportunistic behavior in construction projects as well as lack of reward for those who put in extra effort when adopting an innovation. Also social capital literature shows that those who are able to bridge the gaps between networks (structural holes) are able to get their ideas adopted more easily and so are able to spread their innovations more rapidly. Social capital theory thus appears to be helpful to explain how the diffusion of building product innovation can be improved.