A slab is a component of the construction that may enclose a space vertically. The slab can provide the lower support (floor) or upper construction (roof slab) in any space in a building. Only the core or constructional part of this construction is considered to be a slab. 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 connect. 

There are two main representations for slab occurrences:

• IfcSlab with IfcMaterialLayerSetUsage is used for all occurrences of slabs, that are prismatic and where the thickness parameter can be fully described by the IfcMaterialLayerSetUsage. These slabs are always represented geometrically by a 'SweptSolid' geometry (or by a 'Clipping' geometry based on 'SweptSolid'), if a 3D geometric representation is assigned
• IfcSlab without IfcMaterialLayerSetUsage is used for all other occurrences of slabs, particularly for slabs with changing thickness, or slabs with non planar surfaces, and slabs having only 'SweptSolid' or 'Brep' geometry, or if a more parametric representation is not intended

The following constraints apply to the 'Clipping' representation:

• Solid: IfcExtrudedAreaSolid is required,
• Profile: IfcArbitraryClosedProfileDef, IfcRectangleProfileDef, IfcCircleProfileDef, IfcEllipseProfileDef is supported
• Extrusion: The profile can be extruded perpendicularly or non-perpendicularly to the plane of the swept profile
• Boolean result: The IfcBooleanClippingResult is supported, allowing for Boolean differences between the swept solid (here IfcExtrudedAreaSolid) and one or several IfcHalfSpaceSolid

The image below illustrates a 'Clipping' geometric representation with definition of a roof slab using advanced geometric representation. The profile is extruded non-perpendicular and the slab body is clipped at the eave. 

The following constraints apply to the 'SweptSolid' representation: 

• Solid: IfcExtrudedAreaSolid is required
• Profile: IfcArbitraryClosedProfileDef, IfcRectangleProfileDef, IfcCircleProfileDef, IfcEllipseProfileDef is supported
• Extrusion: The profile can be extruded perpendicularly or non-perpendicularly to the plane of the swept profile

For polygonal slabs, the following interpretation of dimension parameter applies:

• IfcArbitraryClosedProfileDef.OuterCurve: closed bounded curve interpreted as area (or foot print) of the slab.

The image below illustrates the slab body extrusion. 

A slab can be decomposed into parts such as for structural framing and covering panels or topping. For efficiency, each part can reuse geometry using the mapped geometry concept. The image below illustrates how a timber construction slab decomposed into parts. 

The image below illustrates section showing a slab made from precast hollow core panels. 

This concept can be applied to the following resources:

• IfcBuildingElementPart - Parts for other elements
• IfcBeam - Precast hollow core planks or double tee beams in concrete construction, or joists and bearers in timber construction
• IfcCovering - Concrete or topping screeds
• IfcPlate - Used for metal decks at the base of slabs or sheathing

The image below illustrates openings within an aggregated slab which are directly assigned to IfcSlab using IfcRelVoidsElement pointing to IfcOpeningElement and apply to all aggregated parts. If individual parts have cutting and other voiding features, then the decomposed parts have a separate voiding relationship IfcRelVoidsElement pointing to IfcVoidingFeature. 

The image below illustrates assignment of IfcMaterialLayerSetUsage and IfcMaterialLayerSet to the IfcSlabType and the IfcSlab occurrence. 

• It is illegal to assign an IfcMaterialLayerSetUsage to an IfcSlab. Only the subtype IfcSlabStandardCase supports this concept

This concept can be applied to the following resources:

• LoadBearing
• Insulation

This concept can be applied to the following resources:

• IfcSlabType

This concept can be applied to the following resources:

• IfcStructuralSurfaceMember - An idealized structural member corresponding to the slab
• IfcTask - A task for operating on the slab

• Pset_ConcreteElementGeneral
• Pset_PrecastConcreteElementFabrication
• Pset_PrecastConcreteElementGeneral
• Pset_PrecastSlab
• Pset_ReinforcementBarPitchOfSlab
• Pset_SlabCommon
• Pset_TrackBase (only applies to BASESLAB)
• Pset_CessBetweenRails (only applies to TRACKSLAB)
• Pset_EmbeddedTrack (only applies to TRACKSLAB)
• Pset_SlabTypeTrackSlab (only applies to TRACKSLAB)

This concept can be applied to the following resources:

• Qto_SlabBaseQuantities

The IfcSlab, as any subtype of IfcBuildingElement, can participate alternatively in one of the two different containment relationships:

• the Spatial Containment (defined here)
• the Element Composition

The 'Surface' can be used to define a surfacic model of the building (e.g. for analytical purposes, or for reduced Level of Detail representation).