Denmark has in 2019 stated a new climate law aiming to reduce the CO2 emissions, and buildings are causing a considerable amount of the emissions, therefore subject to change. The sustainability certification Deutsche Gesellschaft für Nachhaltiges Bauen (DGNB) is suggested to facilitate the required change in building design by balancing environmental, social, and economic sustainability. DGNB requires implementation of life cycle costing (LCC) and use of the LCCbyg tool to achieve the economic sustainability. However recent literature suggests that LCC is often used to document the decisions when the design is finished, therefore missing the potential of using LCC to ensure the economic sustainability. The present study aimed to understand how building design dynamics affect the implementation and use of LCC during DGNB certifications to discuss the potentials and limitations of implementing and using LCC in future DGNB certified building projects. The cultural-historical activity theory was used as the theoretical framework to design the qualitative interviews with Danish DGNB auditors and Swiss LCC consultants, furthermore a Danish DGNB certified building case study. The case study was based on semi-structured qualitative interviews with the designing architect, cost calculator, DGNB auditor, design and project manager. The case study found missing objectives towards lowering future cost and challenges of informing cost data between the initial and future owner. The present study concludes the missing objectives to lower LCC, resulting in late involvement of the auditor and separation from the building design only using the auditor and LCCbyg tool to document the decisions. Furthermore, the auditor must mask the cost in the LCCbyg to comply with the competitive nature of the building design. The results can potentially direct further study of regulative and normative actions to create a shared objective towards implementing and using LCC during DGNB certifications of buildings.