The dwelling occupancy indexes characterise the occupancy level of the dwelling by comparing the number of rooms it has with the number of rooms that is considered necessary for the household.
The "normal" occupation of a dwelling is defined as follows:
- one living room for the household ;
- one room for each household reference person ;
- one room for other persons married or remarried but not living as a couple, for widowed or divorced persons, and also for single people aged 19 years and older ;
- for single people under 19 years of age, one room for two children if they are of the same sex and if they are under seven years old, otherwise one room per child.
Exceptions: a single person in a studio of 25 m² or more is deemed to meet the standard and dwellings with as many rooms as the standard are considered overcrowded if there is less than 18 m² per person.
Notes: the kitchen is counted in the number of rooms only if it measures more than 12 m².
A dwelling unit with one room less than the standard is moderately over-occupied. If it is two or more rooms short, it is severely over-occupied. Conversely, the dwelling unit is said to be moderately under-occupied if it has one room more than the standard, distinctly over-occupied if it has two rooms more, and very distinctly over-occupied if it has three or more rooms over the standard.