Definition from IAI: a slab (IfcSlab) is a component of the construction that normally encloses a space vertically. The slab may provide the lower surface (floor) or upper surface (roof slab) in any space in a building. It shall be noted, that only the core or constructional part of this construction is considered to be a slap. The upper finish (flooring, roofing) and the lower finish (ceiling, suspended ceiling) are considered to be coverings.
A special type of slab is the landing, described as a floor section to which one or more stair flights or ramp flights connects. May or may not be adjacent to a building storey floor.
The quantities relating to the slab 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 |
| SlabArea | Total area of the extruded area (or foot print) of the slab. The exact definition and calculation rules depend on the method of measurement used. | IfcAreaQuantity |
| SlabVolume | Total volume of the slab. The exact definition and calculation rules depend on the method of measurement used. | IfcVolumeQuantity |
A slab may have openings, such as floor openings. They are defined by an IfcOpeningElement attached to the slab using the inverse relationship HasOpenings pointing to IfcRelVoidsElement.
HISTORY: New entity in IFC Release 2.0, it is a merger of the two previous entities IfcFloor, IfcRoofSlab, introduced in IFC Release 1.0
ISSUES: See issue log for changes made in IFC Release 1.5 and IFC Release 1.5.1, see issue and change log for changes made in IFC Release 2x.
Geometry Use Definitions:
The geometric representation of IfcSlab is given by the IfcProductDefinitionShape, allowing multiple geometric representation. Included are:
NOTE. If the IfcSlab is of type Landing and is used within an IfcStair or IfcRamp, the special agreements to handle stair and ramp geometry will also affect the geometric representation of the IfcSlab.
Local Placement
The local placement for IfcSlab 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 given) to the placement of the local placement of the same IfcSpatialStructureElement, which is used in the ContainedInStructure inverse attribute, or to a spatial structure element at a higher level, referenced by that.
- If the IfcSlab is of type Landing and is used by an IfcStair or IfcRamp, and this container class defines its own local placement, than the PlacementRelTo relationship of IfcLocalPlacement shall point (if given) to the local placement of the aggregate.
- If the relative placement is not used, the absolute placement is defined within the world coordinate system.
Standard Geometric Representation using Swept Solid Representation
The standard geometric representation of IfcSlab is defined using the swept solid representation. The following additional constraints apply to the swept solid representation:
- Solid: IfcExtrudedAreaSolid is required,
- Profile: IfcArbitraryProfileDef shall be supported.
- Extrusion: The profile shall be extruded vertically, i.e., in the direction of the z-axis of the co-ordinate system of the referred spatial structure element. It might be further constraint to be in the direction of the global z-axis in implementers agreements. The extrusion axis shall be perpendicular to the swept profile, i.e. pointing into the direction of the z-axis of the Position of the IfcExtrudedAreaSolid.
In addition: slabs for the standard case shall have only a single material layer.
NOTE in this case the attribute IfcShapeRepresentation.RepresentationType = 'SweptSolid'.
EXAMPLE for standard geometric representation.
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Advanced Geometric Representation using CSG representation
The advanced geometric representation of IfcSlab is defined using the swept area geometry. The following constraints apply to the advanced representation:
- Solid: see standard geometric representation,
- Profile: see standard geometric representation,
- Extrusion: All extrusion directions shall be supported.
- Boolean result: The IfcBooleanClippingResult shall be supported, allowing for Boolean differences between the swept solid (here IfcExtrudedAreaSolid) and one or several IfcHalfSpaceSolid.
NOTE in this case the attribute IfcShapeRepresentation.RepresentationType = 'SweptSolid' or 'CSG'.
EXAMPLE for advanced geometric representation.
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Definition of a roof slab using advanced geometric representation. The profile is extruded non-perpendicular and the slab body is clipped at the eave. |