Every entity in an IFC model has an "IFC Class" Name. For example, wall entities will have an IFC class of IfcWall, and door entities will have an IFC class of IfcDoor. Entities that don't represent individual building elements will also have a class. For example, the project has a class of IfcProject, window types have a class of IfcWindowType, and cost items have a class of IfcCostItem.
Classes aren’t just for categorising entities. They also indicate what types of properties and relationships it is allowed to have. For example, an IfcWall class can have a fire rating property, but an IfcGrid class cannot.
Different IFC schemas have different IFC classes. More recent IFC schemas contain richer and more diverse IFC classes, which you can compare here:
Some entities may also optionally have a Predefined Type. This is a further level of entity categorisation in addition to the IFC Class Name. For example, an IfcWall may have a Predefined Type of SHEAR, or PARTITIONING. Whereas the IFC Class Name is specified by the IFC standard, the Predefined Type may also contain custom values by the user.
The IFC schema documentation contains a list of standard predefined types. Here is how you might find a list of valid Predefined Types for the IFC4X3 schema. The instructions will be similar for all IFC versions.
- Browse to the documentation page for the IFC class you are specifying. You can get there from the list of IFC class names above. For example, this is the IfcWall documentation page.
- Scroll down to the Attributes section of the documentation and find the PredefinedType attribute.
- Click on the enumeration link next to the PredefinedType attribute to view the list of valid values. For example, for an IfcWall, you will click the link to bring you to the documentation for IfcWallTypeEnum.
- A list of valid Predefined Types are shown in a table.
Choosing from the list of standardised Predefined Types is highly recommended. However, if they do not apply to your project you may specify any custom value. For example, you may specify "RADIATIONBARRIER" as a custom PredefinedType for an IfcWall.
One of the most important aspects of writing a specification is to ensure that it applies to the appropriate IFC class. Typically, every single Specification will have an Entity Facet used in its Applicability section.
| Parameter | Required | Restrictions Allowed | Allowed Values | Meaning |
|---|---|---|---|---|
| Name | ✔️ | ✔️ | A valid IFC class from the IFC schema. | The IFC Class must match exactly |
| Predefined Type | ❌ | ✔️ | A valid predefined type from the IFC schema, or any custom text value. | The IFC Predefined Type must match exactly |
| Applicability Intention | Requirement Intention | Facet Definition |
|---|---|---|
| All partition walls | Must be a partition wall | Name="IFCWALL", PredefinedType="PARTITIONING" |
| All floor slabs | Must be a floor slab | Name="IFCSLAB", PredefinedType="FLOOR" |
| All door types, such that may be documented in a door types schedule | Must be a door type | Name="IFCDOORTYPE" |
| All type elements | Must be a type element | Name="IFC.*TYPE" |
| All building storeys | Must be a building storey | Name="IFCBUILDINGSTOREY" |
| All related documents, such as drawings, schedules, manuals, and specifications | Must be a document | Name="IFCDOCUMENTINFORMATION" |
| All distribution systems, such as hot water systems, electrical circuits, etc | Must be a system | Name="IFCSYSTEM" |
| All construction tasks, such as in construction scheduling in a work breakdown structure | Must be a construction task | Name="IFCTASK", PredefinedType="CONSTRUCTION" |