Owners, managers and occupiers of existing buildings are keen to understand if and how enhanced sustainability performance does pay in terms of cost savings. The Building Research Establishment (BRE) says in itís BRE Environmental Assessment Method (BREEAM): ìBREEAM in-use (BiU) is a scheme to help building managers reduce the running costs and improve the environmental performance of existing buildingsî. But so far there is only little evidence available on cost savings that have been achieved by applying the BREEAM in-use standard. This paper is presenting a selection of case studies on BiU certified office and retail properties across Europe. In an online research on literature and BiU, behavioural options of owners, managers and occupiers are studied in order to reach a better understanding of how organisational decisions impact on cost savings. Observations are collected on site-visits at labelled properties. Experience is compiled in interviews with asset managers and sustainability assessors. Finally, the relations between sustainability profiles of certified buildings and best practice behaviour of owners, managers and occupiers are analysed. Conclusions are drawn on recommendations easy to implement for quick cost savings from behavioural improvements along the BiU standard.