A systematic analysis of recently constructed dwellings in the Flemish Region has been undertaken within the SENVIVV-project (1995-1998). In total 200 dwellings have been examined in detail. The study involved various aspects: energy related building data (thermal insulation level, net heating demand, installed heating power, .. ), indoor climate (temperature levels in winter and summer), building airtightness, ventilation, appreciation of the occupants, . . . This paper especially focuses on the results for thermal insulation, airtightness and ventilation. In the field of the thermal insulation several calculations were performed with great care, indicating that a large number of the investigated dwellings does not comply with the Flemish requirements, although it should be no problem from the technical point of view to obtain even much better performances. With respect to the indoor air quality, the presence and performance of ventilation devices was evaluated in all 200 dwellings. A comparison was made with the requirements of the Belgian ventilation standard. The results seem to be rather disappointing. Measurements of the airtightness were performed in 50 dwellings, revealing that the global airtightness is often very bad, while some rooms are very airtight.