The Dutch housing stock consists for about 70% of single family houses with an average N50 of about 7-9 ACH and for 30% of apartments with an average N50 of about 3-4 ACH.New single family houses are much more airtight. In the period 1970 to 2000 the air tightness increased to an N50 of about 3 - 4 ACH. Apartments have nowadays about the same or a slightly better air tightness then before 1970.Another trend is the downward tendency of occupant numbers per dwelling. During 1982 to 2000 inthe Netherlands the average number of occupants per dwelling decreased from 2.8 with 21% to 2.3persons per dwelling.These two trends can have an impact on the choice of a ventilation system when dwellings from acertain period need to be retrofitted. The question is e.g. whether demand controlled ventilation has an added value depending on the air tightness and occupancy of the dwelling.In the framework of the RESHYVENT project this study comprises COMIS simulations to investigatethe relation between occupancy/air tightness and demand controlled ventilation. Based on indoor airquality (IAQ) and energy consumption a comparison has been made between the situation with theexhaust continuously at 21 dm3/s and all supply provisions closed and the situation that a ventilationstrategy such as demand controlled ventilation is applied.The paper gives a positive answer on the applicability of demand controlled ventilation regardlessoccupancy and air tightness. Even at low air tightness (N50>16 ACH), from IAQ point of view demand control is interesting. With internal mixing (e.g. open doors and/or air heating systems), in combination with supply provisions closed, pollutants can be reduced to the same levels as with demand control, however this can also lead to a undesired spread of local pollutants. Through a good distribution of the supply air, demand control does not result in an increase of the ventilation compared to the situation with supply provisions closed. On the other hand, depending on the occupants behavior, significant energy savings are possible.