# 8.10.3.8 IfcMaterialLayerSetUsage

## 8.10.3.8.1 Semantic definition

The IfcMaterialLayerSetUsage determines the usage of IfcMaterialLayerSet in terms of its location and orientation relative to the associated element geometry. The location of material layer set shall be compatible with the building element geometry (that is, material layers shall fit inside the element geometry). The rules to ensure the compatibility depend on the type of the building element.

The IfcMaterialLayerSetUsage is always assigned to an individual occurrence object (and only to relevant subtypes of IfcElement). The IfcMaterialLayerSet, referenced by ForLayerSet, can however be shared among several occurrence objects. If the element type is available (in other words, an instance of the relevant subtype of IfcElementType exists), then the IfcMaterialLayerSet can be assigned to the element type. The assignment between a subtype of IfcElement and the IfcMaterialLayerSetUsage is handled by IfcRelAssociatesMaterial.

Attribute use definition

The IfcMaterialLayerSetUsage is primarily intended to be associated with planar building elements having a constant thickness. With further agreements on the interpretation of LayerSetDirection, the usage can be extended also to other cases, for example to curved building elements, provided that the material layer thicknesses are constant.

Generally, an element may be layered in any of its primary directions, denoted by its x, y or z axis. The geometry use definitions at each specific type of building element will determine the applicable LayerSetDirection.

The following examples illustrate how the IfcMaterialLayerSetUsage attributes (LayerSetDirection, DirectionSense, OffsetFromReferenceLine) can be used in different cases. Normative material use definitions are documented at each element (how these shall be used).

Figure 1 shows an example of the use of IfcMaterialLayerSetUsage aligned to the axis of a wall.

## 8.10.3.8.4 Formal representation

ENTITY IfcMaterialLayerSetUsage
SUBTYPE OF (IfcMaterialUsageDefinition);
ForLayerSet : IfcMaterialLayerSet;
LayerSetDirection : IfcLayerSetDirectionEnum;
DirectionSense : IfcDirectionSenseEnum;
OffsetFromReferenceLine : IfcLengthMeasure;
ReferenceExtent : OPTIONAL IfcPositiveLengthMeasure;
END_ENTITY;