Organizations in the construction industry are focusing more and more on sustainability. There exist various drivers and barriers (D&B) that can enhance or hinder sustainability in organizations. Research has so far mainly been focused on the primary activities within an organization. Hence, this study focused on the supporting activities (SA). This study researched what the defining moments are in the enhancement of sustainability in the SA of an engineering consultant organization. This qualitative research used the method process research, comprising a case study wherein processes of enhancing sustainability within one organization were mapped. Data for 8 cases was collected through semi-structured interviews and case documentation, within the playing field of the most important D&B. Case data was analyzed through the streams model of decision-making theory, existing of the problem, solution and participant stream. Furthermore, windows of opportunities (WOO) and tipping points (TP) were identified in the processes. The results include different patterns and striking observations. Most problem streams include CO2 emissions. The WOO involved raised awareness or multiple events making the problem more pressing. There were no significant TP identified throughout the cases. It was observed that awareness and intrinsic motivation form the most important drivers. The most important barriers are costs; the lack of support from employees or partners; and the lack of intrinsic motivation in the form of a lack of vision and priority. There were four most striking observations regarding the processes in the case study. The first observation is the intrinsic motivation of individuals playing a big role in the enhancement of sustainability. The second observation involves that the organization seems to hook onto trends and external events. The organization is only picking low hanging fruit, by making use of changes that are already planned or taking place, forming the third observation. The fourth observation comprises that there is a lack of clear goals, vision and priority regarding sustainability within the SA. It is therefore recommended to create a supportive and open environment for individuals that are motivated to enhance sustainability; to make use of external events, trends and of changes that are already lined up, but to not let these external occurrences determine the path towards sustainability; and to develop clear goals and a strategy for sustainability in the SA, for a more integral approach.