IFC - Industry Foundation Classes/IFC materials

This page is relevant to understanding Industry Foundation Classes (IFC). The Industry Foundation Classes (IFC) Category includes all pages related to Industry Foundation Classes (IFC).

IFC can store information about real life materials, and objects can be assigned to materials. Materials may contain attributes like a name and description, and contain physical properties. Some of these properties are part of the IFC standard, such as concrete strength, thermal properties, or mechanical properties, or it may be a custom property defined by the user.

A material may be assigned directly to an object. However, for more complex materials, it is possible to combine multiple materials into a composite material. This composite material is known as a material "set" in IFC, and may then be assigned to an object. There are three distinct types of composite material sets.

• Material layer set (each material within this represents a single layer)
• Material constituent set (each material within this represents a single constituent)
• Material profile set (each material within this represents a single profile)

When a material set is defined, it is sometimes necessary to describe which parts of the geometry a portions of the material set applies to. For example, when an object has a material layer set, we need to describe the thickness of each material layer. When we describe a material set assignment parametrically, this is known as a material set usage. There are two types of parametric usages that can be defined in IFC:

• Material layer set usage
• Material profile set usage

A material may also have a visual style associated with it, such as a colour. When viewing an IFC model, the colour of an object may represent its material.

However, it is also possible for IFC objects to be assigned a visual style or colour that is not associated with a material. This is a common cause for confusion, as users may think a colour represents a material. It is made more confusing by the fact that a visual style may have a name. This name is not the same as a material name, but some BIM software may not make the distinction between them.

A visual style may be used to represent non-material information. One common usecase is when a style correlates with a discipline. For example, all hydraulic objects may be coloured blue, and all mechanical objects may be coloured green. The concept of visual styles is a separate concept to materials, and will not be described further here.

Single Material

The simplest possible material definition is a single material by itself. For example, a stirrup or a pipe might have their material assigned this way. A few attributes are stored with each material.

Attribute	Required	Description
Name	Recommended	This can store the name of the material. If a material is given a unique label or tag that is referenced in documentation annotation or schedules, this is where it should be stored. It is usually a short, coded name.
Description	Recommended	This allows you to write a sentence or so to describe the material in human terms.
Category	Recommended	Sometimes, it is important to broadly categorise materials to isolate them for costing or procurement purposes. There is no strict requirement on what categories are allowed, but it is highly recommended to use the value "Concrete", "Steel" or blank.

It is possible for a single material to have IFC properties assigned to it. The following sets are defined by the buildingSMART standard, and should be available in your BIM authoring application. If you wish to store a property that is not part of the standard, you may be define your own property set.

Property Set	Description
Pset_MaterialCombustion	Used to store chemical properties of combustible materials.
Pset_MaterialCommon	Generic material properties.
Pset_MaterialEnergy	TODO
Pset_MaterialFuel	TODO
Pset_MaterialHygroscopic	TODO
Pset_MaterialMechanical	Useful to describing mechanical properties, usually relevant to structural analysis.
Pset_MaterialOptical	TODO
Pset_MaterialThermal	TODO
Pset_MaterialWater	TODO

Material Constituent Set

A constituent set is made up of individual material constituents. The constituent set itself may be assigned a couple attributes.

Attribute	Required	Description
Name	Recommended	This can store the name of the material constituent set. If a material is given a unique label or tag that is referenced in documentation annotation or schedules, this is where it should be stored. It is usually a short, coded name.
Description	Recommended	This allows you to write a sentence or so to describe the material in human terms.

Each individual material constituent within the set is a single material, as described above, but may include additional attributes to describe the nature of the constituent.

Attribute	Required	Description
Name	Recommended	This is the name of an individual material constituent within the set, such as "Cement"
Description		This allows you to write a sentence or so to describe the material in human terms.
Fraction		This optional attribute may store the percentage of volume or weight that this constituent represents.
Category		This is the purpose of the constituent or the role it plays within the material set.

There are two typical usages of a material constituent set. The first typical usage is where a material is made up of a mixture of constituents, like how concrete is made up of sand, cement, aggregate, etc. Each constituent is mixed together, but represents a "fraction" of the whole material constituent set.

The second typical usage is where a single object is simply made up of different materials in an arbitrary structure. For example, a single window element can be made up of an aluminium frame and a glazed panel. In this case, geometry may be modeled that represents the frame, which is assigned to one constituent, and more geometry may be modeled to represent the panel, which is assigned to another constituent.

Although in this example geometry is modeled for each constituent, this is optional. It is acceptable to have a constituent set without needing to explicitly model each constituent geometrically.

Material Layer Set

A layer set is made up of individual material layers. The layer set itself may be assigned a couple attributes.

Attribute	Required	Description
Name	Recommended	This can store the name of the material layer set. If a material is given a unique label or tag that is referenced in documentation annotation or schedules, this is where it should be stored. It is usually a short, coded name.
Description	Recommended	This allows you to write a sentence or so to describe the material in human terms.

Each individual material layer within the set is a single material, as described above, but may include additional attributes to describe the nature of the layer.

Attribute	Required	Description
Name	Recommended	This is the name of an individual material layer within the set, such as "Brick"
Description		This allows you to write a sentence or so to describe the material in human terms.
LayerThickness	Yes	The thickness of the material layer. The meaning of "thickness" depends on its usage, but is typically a length using the unit settings of the project, like "0.15m". It may be set to zero for thin materials, such as a membrane.
IsVentilated		If this is set to true, it means the layer is an air gap, if set to false, it is a solid material.
Category		This is the purpose of the layer or the role it plays within the material set. It is an arbitrary value, but these values are recommended by buildingSMART: "LoadBearing", "Insulation", or "Finish".
Priority		This is a number that determines how layers overlap at a junction or corner in a building. A layer with a higher priority will displace or protrude into the layer of a lower priority.

A typical usage for material layer set is a wall which is often made of multiple layers, creating a "sandwich" of layers. Example layers in a single wall element may be an outer plasterboard lining, an insulation layer, an air gap, or a steel framing layer.

Material Layer Set Usage

TODO

Material Profile Set

An example of a material profile set with multiple profiles

A profile set is made up of individual material profiles. A profile is a shape or outline of a typical cross section which is extruded along an axis. Typically, this is used for structural analysis, where a material profile helps define its mechanical properties.

Typically, only a single profile would be defined in a profile set. This profile would also typically be parameterised, such as a circular proflie, rectangular profile, or I-shaped profile. This would then be used for a duct, pipe, or a beam.

It is also possible, though less common, to define multiple profiles in a profile set. This results in a composite profile, which is useful for describing complex shapes.

Material Profile Set Usage

TODO

Assignment example

Following diagram shows how materials are related to their object. Any child of IfcObjectDefinition as IfcWall, IfcDuct etc… can get a material assigned this way :