Revit to IFC: An Export Guide - Part 7 - IfcElement - Part 1

Summary

The presenter explains how to export Revit building elements to appropriate IFC classes and control the attributes included in the export. Because Revit categories do not always map directly to IFC classes, default mappings and individual element or type settings may need adjustment.

Review and adjust default IFC class mappings

Open File → Export → IFC → IFC Options to review the default IFC class assigned to each Revit category. Check the mappings against the IFC version being used. For example, Revit’s Plumbing Fixtures category may default to IfcFlowTerminal, while IfcSanitaryTerminal may be more suitable for certain water-related fixtures in IFC4.

Categories can also be set not to export. Export settings can be saved to and loaded from text files, making them easier to share across a project or organization.

Override the IFC class for particular element types

A category’s default mapping may not suit every element. For example, a 50 mm travertine floor finish modeled under Revit Floors may be better exported as an IfcCovering than an IfcSlab. IFC slabs represent structural or constructional slabs, while finishes such as flooring are coverings.

To override the class at the type level:

1. In the type shared-parameter file, add IfcExportAs as a type parameter for the relevant category.
2. Add IfcExportType as a type parameter to control the IFC predefined type.
3. In the element’s type properties, set:
   • IfcExportAs to IfcCoveringType
   • IfcExportType to an appropriate value, such as FLOORING
4. Re-export the model and check the result in an IFC viewer.

The same approach can be used for roof finishes, with ROOFING as the predefined type. Alternatively, include the predefined type directly in IfcExportAs, separated by a period—for example, IfcCoveringType.ROOFING—instead of using IfcExportType. The presenter recommends choosing the method that best fits the project workflow.

Set IFC type attributes to match project documentation

By default, Revit generates IFC names and related attributes from the family name, type name, and element IDs. These defaults may not match drawing codes, schedules, or specifications.

To control attributes at the type level, add shared type parameters such as:

• IfcNameType
• IfcDescriptionType
• IfcTagType

Assign them to the relevant categories, then enter values in the type properties. The presenter demonstrates using drawing or type codes such as RF01 and FL02 to create meaningful IFC type names. After export, the IFC type attributes reflect the values entered in these parameters.

Set IFC occurrence (instance) attributes

Instance parameters can provide IFC data for individual elements. The presenter demonstrates adding or assigning:

• IfcName
• IfcDescription
• IfcObjectType
• IfcTag

Enter these values on the selected element; they will appear in the IFC export. Instance-level data is generally more useful for individually documented objects—such as furniture, doors, and sanitary appliances—than for every instance of a floor.

IfcObjectType is described as a high-level classifier, generally associated with user-defined predefined types. The presenter uses “flooring” as an example, while noting that the appropriate value may not always be clear.

Main lesson

Check the IFC export mapping for the target IFC version, then use shared parameters to override classes, predefined types, and attributes where needed. Verify the exported results in an IFC viewer to ensure they match the project’s intended classification and documentation.

Speakers and sources featured

• Speaker: One presenter demonstrating the workflow.
• Software and references: Autodesk Revit IFC export settings and shared parameters; IFC4 class definitions and inheritance; an IFC viewer referred to in the subtitles as DDS-CAD.