A stair is a vertical passageway allowing occupants to walk (step) from one floor level to another floor level at a different elevation. It may include a landing as an intermediate floor slab. The IfcStair can either be represented:

• as a stair assembly entity that aggregates all parts (stair flight, landing, etc. with own representations)
• as a single stair entity without decomposition including all representation directly at the stair entity

• NOTE: In case of an IfcStair being the aggregate of all parts of the stair the aggregation is handled by the IfcRelAggregates relationship, relating an IfcStair with the related IfcStairFlight and landings, IfcSlab with PredefinedType=LANDING. IfcRailing's belonging to the stair can also be included into the aggregation.

The walking line is represented by a two-dimensional open curve as the axis. The curve is directed into the upward direction (direction has to be interpreted as specified at the subtypes of IfcCurve). 

The image below illustrates stair placement, where the IfcStair defines the local placement for all components and the common 'Axis' representation, and each component has its own 'Body' representation. 

This concept can be applied to the following resources:

• IfcStairFlight - Stairs can be decomposed into stair flights
• IfcSlab - Stairs can be decomposed into stair landing, represented by IfcSlab.PredefinedType=LANDING
• IfcRailing - Stairs can be decomposed into railings for zero, one, or both sides

The material of the IfcStair is defined by the IfcMaterial and attached by the IfcRelAssociatesMaterial.RelatingMaterial. It is accessible by the inverse HasAssociations relationship. Material information can also be specified at the IfcStairType, defining the common attribute data for all occurrences of the same type. It is then accessible by the inverse IsDefinedBy relationship pointing to IfcStair.HasAssociations and via IfcRelAssociatesMaterial.RelatingMaterial to IfcMaterial. If both are specified, then the material directly assigned to IfcStair overrides the material assigned to IfcStairType. 

This concept can be applied to the following resources:

• IfcStairType

The following restriction can be imposed by view definitions or implementer agreements:

• If the IfcStair establishes an aggregate, then all contained elements are placed relative to the IfcStair.ObjectPlacement.

This concept can be applied to the following resources:

• Pset_ConcreteElementGeneral
• Pset_PrecastConcreteElementFabrication
• Pset_PrecastConcreteElementGeneral
• Pset_StairCommon

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

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