Describes the retrofitting of a 14-storey office block in Oslo, done as part of an energy conservation project carried out in Norway 1979-82. The main reduction in energy consumption was achieved by tightening air leaks between concrete wall elements and windows by the application of sealing compound in 2 critical types of joint in the facade. Measures the energy consumption one year before and one year after retrofitting, using thermography to find the air leaks and to verify the tightening afterwards. Also carries out pressurization tests using the building's ventilation system. The leakage at 50 Pa is reduced from 6.3 ach to 3.0 ach. The reduction in energy consumption is 95 Kwh/m2, with a payback period of 1.2 years.