The potential for using the TOBUS methodology to select office building upgrading solutions have been investigated during field tests in 15 European office buildings in 5 European countries. The 15 office buildings represent a variety of building traditions, architectural designs, construction periods and energy and indoor performance. The buildings were audited following the TOBUS methodology developed within the project. The results of the test surveys were primarily used to improve the TOBUS methodology and secondly to suggest general upgrading solutions and energy retrofit measures for the surveyed buildings. This paper describes the development of the TOBUS methodology based on the 15 Lest surveys.