IFC (Industry Foundation Classes) is an open data schema for describing buildings and infrastructure: their elements, spaces, relationships, properties and geometry. It lets models move between software from different vendors, and lets clients keep information in a format no single vendor controls. IFC is maintained by buildingSMART International and published as ISO 16739.
At a glance
| Maintained by | buildingSMART International |
| Standard | ISO 16739-1 |
| Versions in use | IFC 2x3, IFC 4 (ADD2 TC1) and IFC 4.3 (adds infrastructure); see IFC versions |
| File formats | .ifc (STEP text, most common), .ifcXML, .ifcZIP |
| Typical uses | Coordination, model checking, handover, archiving, quantity take-off |
What an IFC file describes
- Spatial structure: project → site → building (or facility) → storeys → spaces.
- Elements: walls, slabs, doors, ducts, pipes, beams, each as an IFC class (IfcWall, IfcDuctSegment…), often with a predefined type.
- Types: shared definitions (a door type) that many occurrences use.
- Properties: values grouped in property sets, such as Pset_WallCommon with FireRating and IsExternal; and quantities in quantity sets.
- Relationships: containment in a storey, aggregation into assemblies, connections, openings and voids.
- Classification and materials.
- Geometry: as solids, extrusions, meshes or boundary representations, with placements relative to each other.
- Identity: every object has a GlobalId (GUID) that should stay the same between exports.
How it is used on projects
- Coordination: each discipline exports IFC; the models are federated and checked for clashes.
- Checking: requirements written as IDS are checked against the IFC export.
- Handover: the client receives IFC as a long-term, open record, often with COBie data.
- Reuse: quantities, schedules and data can be read from IFC by tools that never saw the native model.
Limits to know
- IFC is an exchange format, not a live editing format. Round trips (edit, export, re-import) usually lose information.
- An export is only as good as its mapping: elements the tool cannot classify become IfcBuildingElementProxy.
- Different tools support different MVDs (subsets of the schema); what one exports, another may not read fully.
- Geometry may arrive as dumb meshes, which are fine for coordination but not for editing.
Common mistakes
- Exporting with default settings and no mapping of classes and properties.
- New GUIDs on every export, which breaks BCF references and model comparison.
- Wrong storey assignments, so elements appear on the wrong level.
- Leaving out the georeference (IfcMapConversion), so models do not line up.
Where to read more
buildingSMART International publishes the schema documentation for each version. Software vendors publish export guides for their tools; the project's BEP should name the IFC version and export settings.