bSIIndustry Foundation Classes (IFC) is the primary open data standard for Building Information Modeling (BIM) interoperability. Standardized as ISO 16739-1:2024, IFC defines a comprehensive, platform-neutral schema for describing the physical and functional characteristics of buildings and infrastructure throughout their lifecycle, from design through construction, operation, and demolition.
Background
The IFC initiative began in 1994 when Autodesk formed an industry consortium of twelve US companies — including AT&T, HOK Architects, Honeywell, and others — to develop a set of C++ classes supporting integrated application development for the construction industry. Initially named the Industry Alliance for Interoperability, the organization opened to all interested parties in 1995 and was renamed the International Alliance for Interoperability in 1997. A further renaming in 2005 established the current maintainer, buildingSMART International. IFC 1.0 was released in June 1996, and the specification has evolved through numerous versions, with IFC4.3 Add2 (2024) being the most recent.
Purpose & Scope
IFC provides a data model for the entire built environment, organized around an EXPRESS-based entity-relationship model with hundreds of entities in an object-based inheritance hierarchy. The model covers:
- Spatial elements — sites, buildings, storeys, and spaces
- Physical elements — walls, beams, doors, windows, slabs, stairs, and distribution elements (HVAC, electrical, plumbing)
- Processes — tasks, events, and procedures with scheduling and sequencing
- Resources — materials, labor, equipment, and cost information
- Relationships — composition, assignment, connectivity, association, and type definition
At the most abstract level, all entities derive from either rooted entities (with GUID identity, name, and revision control) or non-rooted entities (existing only by reference from rooted instances).
File Formats
IFC supports multiple encodings of the same underlying data:
| Format | Extension | Description |
|---|---|---|
| IFC-SPF | .ifc | STEP Physical File (ISO 10303-21), most widely used |
| IFC-XML | .ifcXML | XML encoding (ISO 10303-28) |
| IFC-ZIP | .ifcZIP | Compressed SPF or XML |
| IFC-Turtle | .ttl | RDF Turtle using ifcOWL ontology |
| ifcJSON | .json | JSON encoding for web applications |
| ifcHDF | .hdf | HDF5 binary format (ISO 10303-26) |
Governance & Maintenance
IFC is developed and maintained by buildingSMART International, a non-profit organization. The specification process involves working groups, public review periods, and formal ratification. Several governments mandate IFC use for public building projects, including Denmark (since 2010) and Finland (Senate Properties, since 2017).
Notable Implementations
IFC is supported by virtually all major BIM software platforms, including Autodesk Revit, Graphisoft Archicad, Bentley MicroStation, Trimble Tekla Structures, Nemetschek Allplan, and the open-source FreeCAD. The standard is central to openBIM workflows and is required by many public sector clients worldwide.
Related Standards
IFC operates within a broader buildingSMART ecosystem including the BIM Collaboration Format (BCF) for issue tracking and the Information Delivery Specification (IDS) for exchange requirements.