IFC (Industry Foundation Classes) is the open, vendor-neutral file format for sharing BIM models between different software. An IFC model is a BIM model saved in that format - a .ifc file holding the building's elements, such as walls, doors and pipes, with their geometry, properties and relationships - so Revit, Archicad, Tekla and many other tools can all read it.
Some see IFC as the glue that could hold the construction and building industry together - well, at least when it comes to sharing building information about a project.
1) What is IFC?
An IFC file is a model file created in the Industry Foundation Classes (IFC) format, an open file format used by Building Information Modeling (BIM) programs. It contains a building or facility model, including its spatial structure, elements, materials, properties and shapes. (IFC is the full form in BIM; on a drawing issue sheet the same three letters usually mean "issued for construction", one of the BIM acronyms with two meanings.)
IFC is the technical core of buildingSMART International, which develops it. It was first published as an ISO standard in 2013, updated as ISO 16739-1:2018 and again in 2024 (IFC 4.3, ISO 16739-1:2024). It's an open, vendor-neutral data model that lets BIM content move between software and companies without everyone needing the same tools.
2) What are IFC models?
An IFC model is what you get when a BIM authoring tool exports its native model (a Revit .rvt, an Archicad .pln) to IFC. IFC model files can then be imported into, or referenced by, many other kinds of BIM (Building Information Modeling) software. This allows for better collaboration between different teams working on a project, as everyone has access to the same information.
On most projects each discipline exports its own IFC model, and the BIM coordinator combines them into a federated model to check for clashes and missing information. Treat the IFC as a reference: fix things in the native model and export again.
3) What is the IFC data format/IFC schema?
The IFC data format stores and exchanges information about a construction project: the geometry, materials and quantities of building elements, and the spatial relationships between them.
The IFC schema is the set of rules that defines what can be included in an IFC file and how the data elements relate to each other: every element has a class (IfcWall, IfcDoor, IfcPipeSegment), a globally unique ID and property sets. The schema itself is written in the EXPRESS data modelling language. Most IFC files are saved as plain text in the STEP format (.ifc), and the same data can also be written as XML (.ifcXML) or zipped (.ifcZIP).
The main versions you'll meet are:
- IFC2x3 - released in 2006 and still very widely used, especially for coordination.
- IFC4 - published in 2013 as the first ISO edition (ISO 16739), with better geometry and property definitions.
- IFC 4.3 - adds infrastructure: roads, railways, bridges, ports and waterways. It became ISO 16739-1:2024 and is now the latest official version.
- IFC5 - the next generation, still in development at buildingSMART.
Not sure which to use? The one your project's BIM execution plan asks for, as long as every tool in the chain can read it.
4) BIM and IFC for Interoperability
IFC files are an essential part of Building Information Modeling (BIM) because they enable interoperability between different software and better collaboration between different teams.
IFC files can be used to transfer data between BIM software, such as Autodesk Revit and Bentley MicroStation, or other project management software, so everyone has the same information whichever tools they chose. Working this way, with open standards, is called openBIM.
5) How does IFC work?
The IFC format lets users translate their native data into a common structure that other software can read. When you export, the authoring tool maps each of its objects to an IFC class (a Revit wall becomes an IfcWall), writes out its geometry and properties, and gives it a GlobalId that stays the same from one export to the next. The receiving software reads those classes and properties back in.
That mapping is where most IFC problems start: wrong export settings lose properties, put elements in the wrong class or move the model off the shared coordinates. So agree the export settings in the BEP and check every team's first export before the real exchanges begin.
6) What does an IFC BIM file contain?
It contains building geometry and building data - everything that was exported from the BIM file, or a subset of it:
- The spatial structure: project, site, building, storeys and spaces.
- The elements and their geometry: walls, slabs, doors, ducts and pipes, each with its type, shape and position.
- Properties and quantities: grouped in property sets, such as fire rating, material, area or volume.
- Classification: references to systems such as Uniclass or OmniClass.
- Relationships: which storey an element is on, which system it belongs to, what's connected to what.
Transforming native data into an IFC file is how that information moves between applications.
7) BIM data exchange formats
Exchange formats for BIM data help the different stakeholders in a project collaborate. IFC is the best known, but buildingSMART publishes a family of open standards that work together:
- IFC - the model itself.
- BCF (BIM Collaboration Format) - issues and clashes, with a viewpoint, passed between tools.
- IDS (Information Delivery Specification) - the requirements a model must meet, as a file checking tools can read. Here's how to use IDS in your BIM workflow.
- bSDD (buildingSMART Data Dictionary) - shared definitions of classes and properties.
- COBie - asset information handed over to the owner, often produced from IFC.
The free lesson openBIM principles and tools explains how the standards fit together, and the openBIM and buildingSMART standards slides (PDF) (opens in a new tab) are free to download.
8) How to open an IFC file?
Many software applications support the IFC format, including:
- Autodesk Revit
- Bentley Systems MicroStation
- Graphisoft ArchiCAD
- Dassault Systèmes SolidWorks
- Trimble SketchUp
- Nemetschek Allplan
- Tekla Structures
Some applications are designed specifically for viewing, reviewing and checking IFC data rather than authoring it, and several vendors offer free IFC viewers.
Plannerly is one of these applications. With Plannerly's Verify module, you can view, interrogate and check IFC files - see the free lessons on 3D model navigation and linking models for auto-checking.
Open-source tools such as IfcOpenShell and Bonsai (formerly BlenderBIM) work with IFC files too.
Not every application can use all of the data in an IFC file, and different applications can show the same data differently, so check that your software works with the IFC data - and version - you have.
How to check an IFC model against your requirements
Opening an IFC model is the easy part. The real question is: does it contain what we asked for, for this milestone?
That's what IDS is for. In Plannerly you write the requirements once and export them as an IDS file, so each team can check its own IFC models before it submits, and Verify checks every delivered model version against the same requirements, element by element. Start with the free lesson Model checking intro, download the free IDS checking slides (PDF) (opens in a new tab), or follow the step-by-step guide to checking every model with IDS.
Summary
IFC is an open international standard that makes different BIM software work together. IFC files contain building geometry and data, and most proprietary and open-source BIM tools support them. Pick the version your project asks for, agree the export settings up front, and check every model you receive.
Plannerly can open IFC files and check them against your project's requirements, which makes it easy for different teams to work together and share project data. Try Plannerly for free.
Keep reading: what is openBIM? 10 critical things you must know, how one team saved over 4 million euros with BIM and why you need a BIM manager.
I blog for the Five BIM Bloggers series, where every week we share different perspectives on important BIM topics. To hear our views first, join Plannerly free or browse the Plannerly BIM blog.
