A crucial part of the project was to base the work on real buildings and to assess actual performance characteristics and energy use. Audits and measurements were conducted at site. Audits included inspections of the design, types, and condition of building components and systems. Instantaneous and 2-week measurements were made on building and component dimensions, indoor temperatures, ventilation rates, and air tightness of one apartment per building. Together with design drawings (if available), energy bills, energy performance certificates, and mandatory ventilation inspection protocols, these data were used for models in BES programs BV2 (Nilsson 1997) or IDA-ICE (Sahlin et al. 2004). The base models of the buildings were validated to give annual energy use as close as possible to collected (billed) energy. Having this done, the next step was to test various ECM alternatives to quantify energy savings, reduced CO2-eq emissions and life cycle costs.