Count both occupied and vacant apartments in the house or building. Do not count stores or office space.

Detached means there is open space on all sides, or the house is joined only to a shed or garage. Attached means that the house is joined to another house or building by at least one wall that goes from ground to roof. An example of A one-family house attached to one or more houses is a house in a row of houses attached to one another, sometimes referred to as a townhouse.

A mobile home that has had one or more rooms added or built onto it should be considered as A one-family house detached from any other house. If only a porch or shed has been added to a mobile home, it should be considered as a mobile home.