#### IfcBuilding

Natural language names

##### Semantic definitions at the entity

Entity definition

Definition from ISO 6707-1:1989: 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.

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:

- COMPLEX = building complex
- ELEMENT = building
- PARTIAL = building section

> 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:

- Pset_BuildingCommon: common property set for all types of buildings
- Pset_BuildingWaterStorage: specific property set for buildings to capture the water supply requirements
- Pset_BuildingUse: specific property set for buildings to capture the current and anticipated real estate context.
- Pset_BuildingUseAdjacent: specific property set for buildings to capture the use information about the adjacent buildings.

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:

- IfcBuilding.Decomposes -- referencing (IfcSite || IfcBuilding) by IfcRelAggregates.RelatingObject, If it refers to another instance of IfcBuilding, the referenced IfcBuilding needs to have a different and higher CompositionType, i.e. COMPLEX (if the other IfcBuilding has ELEMENT), or ELEMENT (if the other IfcBuilding has PARTIAL).
- IfcBuilding.IsDecomposedBy -- referencing (IfcBuilding || IfcBuildingStorey) by IfcRelAggregates.RelatedObjects. If it refers to another instance of IfcBuilding, the referenced IfcBuilding needs to have a different and lower CompositionType, i.e. ELEMENT (if the other IfcBuilding has COMPLEX), or PARTIAL (if the other IfcBuilding has ELEMENT).

If there are building elements and/or other elements directly related to the IfcBuilding (like a curtain wall spanning several stories), they are associated with the IfcBuilding by using the objectified relationship IfcRelContainedInSpatialStructure. The IfcBuilding references them by its inverse relationship:

- IfcBuilding.ContainsElements -- referencing any subtype of IfcProduct (with the exception of other spatial structure element) by IfcRelContainedInSpatialStructure.RelatedElements.

| 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.

- The PlacementRelTo relationship of IfcLocalPlacement shall point (if relative placement is used) to the IfcSpatialStructureElement of type IfcSite, or of type IfcBuilding (e.g. to position a building relative to a building complex, or a building section to a building).
- If the relative placement is not used, the absolute placement is defined within the world coordinate system.

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:

- IfcShapeRepresentation.RepresentationIdentifier = 'FootPrint'
- IfcShapeRepresentation.RepresentationType = 'GeometricCurveSet'

Body Representation

The body (or solid model) geometric representation (if the building has an independent geometric representation) of IfcBuilding is defined using faceted B-Rep capabilities (with or without voids), based on the IfcFacetedBrep or on the IfcFacetedBrepWithVoids.

The representation identifier and type of this representation of IfcBuilding is:

- IfcShapeRepresentation.RepresentationIdentifier = 'Body'
- IfcShapeRepresentation.RepresentationType = 'Brep'

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.

Attribute definitions

# | Attribute | Type | Cardinality | Description | A
--- | --- | --- | --- | --- | ---
10 | ElevationOfRefHeight | - |  | This attribute is out of scope for this model view definition and shall not be set. |
11 | ElevationOfTerrain | - |  | This attribute is out of scope for this model view definition and shall not be set. |
12 | BuildingAddress | - |  | This attribute is out of scope for this model view definition and shall not be set. |

##### Inherited definitions from supertypes

Entity inheritance
Attribute inheritance

# | Attribute | Type | Cardinality | Description | A
--- | --- | --- | --- | --- | ---
IfcRoot
1 | GlobalId | IfcGloballyUniqueId | [1:1] | Assignment of a globally unique identifier within the entire software world. | X
2 | OwnerHistory | IfcOwnerHistory | [1:1] | Assignment of the information about the current ownership of that object, including owning actor, application, local identification and information captured about the recent changes of the object, NOTE: only the last modification in stored. | X
3 | Name | IfcLabel | [0:1] | Optional name for use by the participating software systems or users. For some subtypes of IfcRoot the insertion of the Name attribute may be required. This would be enforced by a where rule. | X
4 | Description | IfcText | [0:1] | Optional description, provided for exchanging informative comments. | X
IfcObjectDefinition
| IsDecomposedBy | IfcRelDecomposes @RelatingObject | S[0:?] | Reference to the decomposition relationship, that allows this object to be the composition of other objects. An object can be decomposed by several other objects. | X
| Decomposes | IfcRelDecomposes @RelatedObjects | S[0:1] | References to the decomposition relationship, that allows this object to be a part of the decomposition. An object can only be part of a single decomposition (to allow hierarchical strutures only). | X
| HasAssociations | IfcRelAssociates @RelatedObjects | S[0:?] | Reference to the relationship objects, that associates external references or other resource definitions to the object.. Examples are the association to library, documentation or classification. | X
IfcObject
5 | ObjectType | IfcLabel | [0:1] | The type denotes a particular type that indicates the object further. The use has to be established at the level of instantiable subtypes. In particular it holds the user defined type, if the enumeration of the attribute PredefinedType is set to USERDEFINED. | X
| IsDefinedBy | IfcRelDefines @RelatedObjects | S[0:?] | Set of relationships to type or property (statically or dynamically defined) information that further define the object. In case of type information, the associated IfcTypeObject contains the specific information (or type, or style), that is common to all instances of IfcObject referring to the same type. | X
IfcProduct
6 | ObjectPlacement | IfcObjectPlacement | [0:1] | Placement of the product in space, the placement can either be absolute (relative to the world coordinate system), relative (relative to the object placement of another product), or constraint (e.g. relative to grid axes). It is determined by the various subtypes of IfcObjectPlacement, which includes the axis placement information to determine the transformation for the object coordinate system. | X
7 | Representation | IfcProductRepresentation | [0:1] | Reference to the representations of the product, being either a representation (IfcProductRepresentation) or as a special case a shape representations (IfcProductDefinitionShape). The product definition shape provides for multiple geometric representations of the shape property of the object within the same object coordinate system, defined by the object placement. | X
IfcSpatialStructureElement
8 | LongName | - |  | This attribute is out of scope for this model view definition and shall not be set. |
9 | CompositionType | IfcElementCompositionEnum | [1:1] | Denotes, whether the predefined spatial structure element represents itself, or an aggregate (complex) or a part (part). The interpretation is given separately for each subtype of spatial structure element. | X
| ContainsElements | IfcRelContainedInSpatialStructure @RelatingStructure | S[0:?] | Set of spatial containment relationships, that holds those elements, which are contained within this element of the project spatial structure. NOTE The spatial containment relationship, established by IfcRelContainedInSpatialStructure, is required to be an hierarchical relationship, i.e. each element can only be assigned to 0 or 1 spatial structure element. | X
IfcBuilding
10 | ElevationOfRefHeight | - |  | This attribute is out of scope for this model view definition and shall not be set. |
11 | ElevationOfTerrain | - |  | This attribute is out of scope for this model view definition and shall not be set. |
12 | BuildingAddress | - |  | This attribute is out of scope for this model view definition and shall not be set. |

##### Definitions applying to AISC Model View

Instance diagram

Concept usage

Spatial Composition

The Spatial Composition concept applies to this entity.

Exchange |
--- | ---
Import | R
Export | R

Spatial Decomposition

The Spatial Decomposition concept applies to this entity.

Exchange |
--- | ---
Import | R
Export | R

Concept inheritance

# | Concept | Model View
--- | --- | ---
IfcBuilding
| Spatial Composition | AISC Model View
| Spatial Decomposition | AISC Model View

##### Formal representations

XSD Specification
`<xs:element name="IfcBuilding" type="ifc:IfcBuilding" substitutionGroup="ifc:IfcSpatialStructureElement" nillable="true"/>
<xs:complexType name="IfcBuilding">
<xs:complexContent>
<xs:extension base="ifc:IfcSpatialStructureElement"/>
</xs:complexContent>
</xs:complexType>
`
EXPRESS Specification
`ENTITY IfcBuilding
SUBTYPE OF (IfcSpatialStructureElement);
ElevationOfRefHeight : OPTIONAL IfcStrippedOptional;
ElevationOfTerrain : OPTIONAL IfcStrippedOptional;
BuildingAddress : OPTIONAL IfcStrippedOptional;
END_ENTITY;

EXPRESS-G diagram

`

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