A building is a roofed construction which:
- can be used separately;
- has been built for permanent purposes;
- can be entered by persons;
- is suitable or intended for protecting persons, animals or objects.
Buildings do not necessarily need walls. It is sufficient for them to have a roof, but there must be a demarcation which constitutes the individual character of the building to be used separately.
A separate building is any free-standing building; also, in the case of interconnected structures (e.g. semi-detached or terraced houses), any unit separated from other units by a fire wall extending from roof to cellar is considered an individual building. If there is no fire wall the interconnected building units are regarded as individual buildings if they have their own access (own entrance) as well as their own utility system and are separately usable.
For technical reasons, buildings also include separately usable underground constructions which can be entered by persons and are suitable or intended for protecting persons, animals or objects (e.g. underground shelters, underground hospitals, underground shopping centers and workshops, underground garages).
Buildings are subdivided into residential and non-residential buildings. A residential building is a building at least half of which is used for residential purposes. If less than half of the overall useful floor area is used for residential purposes, the building is classified under non-residential buildings in accordance with its purpose-oriented design.
A non-residential building is a building which is mainly used or intended for non-residential purposes. If at least half of the overall useful floor area is used for residential purposes, the building is classified as a residential building.