IfcBuilding
Definition from ISO 67071:1989: Construction work that has the provision of shelter for its occupants or contents as one of its main purpose and is normally designed to stand permanently in one place.
Definition from buildingSMART: A building represents a structure that provides shelter for its occupants or contents and stands in one place. The building is also used to provide a basic element within the spatial structure hierarchy for the components of a building project (together with site, storey, and space).
A building is (if specified) associated to a site. A building may span over several connected or disconnected buildings. Therefore building complex provides for a collection of buildings included in a site. A building can also be decomposed in (vertical) parts, where each part defines a building section. This is defined by the composition type attribute of the supertype IfcSpatialStructureElements which is interpreted as follow:
HISTORY New entity in IFC Release 1.0.
Property Set Use Definition:
The property sets relating to the IfcBuilding are defined by the IfcPropertySet and attached by the IfcRelDefinesByProperties relationship. It is accessible by the inverse IsDefinedBy relationship. The following property set definitions specific to the IfcBuilding are part of this IFC release:
Quantity Use Definition:
The quantities relating to the IfcBuilding are defined by the IfcElementQuantity and attached by the IfcRelDefinesByProperties. The following quantities are foreseen, but will be subjected to the local standard of measurement:
Name  Description  Value Type 
NominalHeight  Calculated height of the building, measured from the level of terrain to the top part of the building. The exact definition and calculation rules depend on the method of measurement used.  IfcQuantityLength 
NominalArea  Calculated coverage of the site area that is occupied by the building (also referred to as footprint). The exact definition and calculation rules depend on the method of measurement used.  IfcQuantityArea 
GrossFloorArea  Calculated sum of all areas covered by the building (normally including the area of construction elements). The exact definition and calculation rules depend on the method of measurement used.  IfcQuantityArea 
NetFloorArea  Calculated sum of all usable areas covered by the building (normally excluding the area of construction elements). The exact definition and calculation rules depend on the method of measurement used.  IfcQuantityArea 
GrossVolume  Calculated gross volume of all areas enclosed by the building (normally including the area of construction elements). The exact definition and calculation rules depend on the method of measurement used.  IfcQuantityVolume 
NetVolume  Calculated net volume of all areas enclosed by the building (normally excluding the area of construction elements). The exact definition and calculation rules depend on the method of measurement used.  IfcQuantityVolume 
Spatial Structure Use Definition
The IfcBuilding is used to build the spatial structure of a building (that serves as the primary project breakdown and is required to be hierarchical). The spatial structure elements are linked together by using the objectified relationship IfcRelAggregates. The IfcBuilding references them by its inverse relationships:
Figure shows the IfcBuilding as part of the spatial structure. In this example, both the IfcBuilding and the referenced IfcBuildingStorey have products contained. There is no definition on the level of product subtypes about which particular element can (only) be assigned to an IfcBuilding or an IfcBuildingStorey 
Attribute Use Definition:
The heated space within a Building shall be handled by the IfcZone, including the property for overall height of the heated space in the Building. The following figure shall define the interpretation of building heights and elevations for IfcBuilding. The ElevationOfRefHeight is used to give the height above sea level of the internal height 0.00. The height 0.00 is often used as a building internal reference height and equal to the floor finish level of the ground floor. 
Geometry Use Definitions:
The geometric representation of IfcBuilding is given by the IfcProductDefinitionShape and IfcLocalPlacement, allowing multiple geometric representation.
Local Placement
The local placement for IfcBuilding is defined in its supertype IfcProduct. It is defined by the IfcLocalPlacement, which defines the local coordinate system that is referenced by all geometric representations.
Geometric Representations
Currently, the use of a 2D 'FootPrint' representation of type 'GeometricCurveSet' and a 3D 'Body' representation of type 'Brep' is supported.
Foot Print Representation
The foot print representation of IfcBuilding is given by either a single 2D curve (such as IfcPolyline or IfcCompositeCurve), or by a list of 2D curves (in case of inner boundaries), if the building has an independent geometric representation.
The representation identifier and type of this geometric representation of IfcBuilding is:
Body Representation
The body (or solid model) geometric representation (if the building has an independent geometric representation) of IfcBuilding is defined using faceted BRep capabilities (with or without voids), based on the IfcFacetedBrep or on the IfcFacetedBrepWithVoids.
The representation identifier and type of this representation of IfcBuilding is:
Since the building shape is usually described by the exterior building elements, an independent shape representation shall only be given, if the building is exposed independently from its constituting elements.
EXPRESS specification:

ElevationOfRefHeight  :  Elevation above sea level of the reference height used for all storey elevation measures, equals to height 0.0. It is usually the ground floor level. 
ElevationOfTerrain  :  Elevation above the minimal terrain level around the foot print of the building, given in elevation above sea level. 
BuildingAddress  :  Address given to the building for postal purposes. 
