What Is an IFC File? How to Open, Edit and Check One

An IFC file is an open, vendor-neutral file for building models, defined by buildingSMART and published as the international standard ISO 16739. It stores a building as a list of real things, such as walls, doors, windows, rooms and storeys, together with their 3D shape and how they relate to each other, so Revit, Archicad, Tekla, Vectorworks and free viewers can all read the same model. The file extension is .ifc, and the file itself is plain text you can open in any editor.

That is the short answer. The rest of this guide shows a real IFC file line by line, the free ways to open and edit one, and an honest audit of the IFC files our own product exports, because writing them every day taught us more about what goes wrong than any spec did.

What is an IFC file?

IFC stands for Industry Foundation Classes. The idea goes back to 1994, when Autodesk set up an industry consortium to agree on shared classes for building software; that group became the International Alliance for Interoperability and, in 2005, buildingSMART, which still maintains the standard. Because buildingSMART publishes it through ISO, no single vendor owns IFC, and that is the whole point: it is the format you use when a model has to leave the program it was made in.

IFC file (definition): a building information model saved in the Industry Foundation Classes schema (ISO 16739), usually as a .ifc text file in the STEP format (ISO 10303-21), that describes building elements, spaces, their geometry, their properties and the relationships between them.

What makes IFC different from a mesh format like OBJ or FBX is meaning. An OBJ file knows it has a few thousand triangles. An IFC file knows that a particular set of geometry is an IfcWall on the ground floor named "W-S", that it has two IfcWindow objects sitting in openings cut into it, and that the room behind it is an IfcSpace called "Living / Dining / Kitchen". That is why IFC is the exchange format for BIM and OBJ is not.

One building, three discipline models: structure, rebar and architecture. IFC is how models like these meet when the teams work in different software. Reference: BIM Portfolio by Hemant Pratap Singh on Behance.

It also explains IFC's reputation. The format can carry a lot of information, but nothing forces the software that writes it to fill that information in. A file that opens fine can still be nearly useless to the engineer who receives it. More on that in the audit below.

What is inside an IFC file? A real one, opened line by line

The best way to understand the IFC file format is to read one. This is a complete, valid IFC4 file exported by our engine at the very start of a project, before the AI agent had placed a single wall. It is 24 lines and 1 KB:

ISO-10303-21;
HEADER;
FILE_DESCRIPTION(('ViewDefinition [CoordinationView]'),'2;1');
FILE_NAME('','2026-10-24T16:34:35',(''),(''),'IfcOpenShell 0.9.0post1+b5e509b','IfcOpenShell 0.9.0post1+b5e509b','');
FILE_SCHEMA(('IFC4'));
ENDSEC;
DATA;
#1=IFCPROJECT('3VSrl5Knb4JQV5IErMtkMS',$,'AI BIM demo',$,$,$,$,(#10),#5);
#2=IFCSIUNIT(*,.LENGTHUNIT.,$,.METRE.);
#3=IFCSIUNIT(*,.AREAUNIT.,$,.SQUARE_METRE.);
#4=IFCSIUNIT(*,.VOLUMEUNIT.,$,.CUBIC_METRE.);
#5=IFCUNITASSIGNMENT((#4,#2,#3));
#6=IFCCARTESIANPOINT((0.,0.,0.));
#7=IFCDIRECTION((0.,0.,1.));
#8=IFCDIRECTION((1.,0.,0.));
#9=IFCAXIS2PLACEMENT3D(#6,#7,#8);
#10=IFCGEOMETRICREPRESENTATIONCONTEXT($,'Model',3,1.E-05,#9,$);
#11=IFCGEOMETRICREPRESENTATIONSUBCONTEXT('Body','Model',*,*,*,*,#10,$,.MODEL_VIEW.,$);
#12=IFCSITE('2j814J4LT6$QsAvfI$F4Vm',$,'Site',$,$,$,$,$,$,$,$,$,$,$);
#13=IFCBUILDING('3_DYn31i105Azs_AmzYWjh',$,'Building',$,$,$,$,$,$,$,$,$);
#14=IFCRELAGGREGATES('0MQtheVvDCkRCOyI8Mqxyv',$,$,$,#1,(#12));
#15=IFCRELAGGREGATES('3qD5juIAbEAgTBheJml0v$',$,$,$,#12,(#13));
ENDSEC;
END-ISO-10303-21;

Here is how to read it:

• The HEADER says which schema the file uses (IFC4), which program wrote it and when. FILE_SCHEMA is the line to check first when a program refuses to open a file: an IFC2x3-only tool will reject an IFC4 header outright.
• The DATA section is one object per line. #1, #2 and so on are line numbers that other lines point to. #5 collects the units from lines #2 to #4, and the project on line #1 points at #5, so the whole model is in metres.
• The 22-character strings such as '3VSrl5Knb4JQV5IErMtkMS' are GlobalIds: compressed GUIDs that stay with an object for its whole life. They are how clash reports, BCF issues and model comparisons recognise "the same wall" across two versions of a file.
• $ means "not set" and * means "derived". Count the $ signs on the IFCSITE line: the site has no address, no coordinates and no elevation. That is legal IFC, and it is also the first sign of a thin export.
• The two IFCRELAGGREGATES lines build the spatial tree: the project contains the site, and the site contains the building. In a full model the chain continues to storeys, and every wall, door and room is attached to a storey.

A full model just adds more lines of the same kind. The single-storey house below is 1,798 lines. Two of them, unchanged from the file:

#240=IFCDOOR('2GmS4H_J5DyO$DHCGStD61',$,'Front door',$,$,#325,#314,$,$,$,$,$,$);
#1837=IFCSPACE('1v6TlARDbA6eP_s4aHgByw',$,'Living / Dining / Kitchen \X2\00B7\X0\ 57.7 m\X2\00B2\X0\',$,$,#1855,#1844,$,$,$,$);

The \X2\00B7\X0\ is how STEP stores characters outside basic ASCII, here a middle dot and a superscript 2. Every IFC reader decodes it, but it is why a plain text search for "m²" inside an IFC file finds nothing.

Exported to IFC, every wall, door, window, stair and piece of furniture in a model like this becomes its own line with its own GlobalId, the same way the front door does above. Reference: Villa Design in KSA by Omar Alaa on Behance.

The rooms are in there too. Drawing only the IfcSpace, IfcWall, IfcDoor and IfcWindow entities from that file, top down, gives you a floor plan without any drawing ever having been exported:

Six IfcSpace rooms, 113.1 m² in total, plotted from the IFC with about 40 lines of Python. The names and areas come straight from the file. We cut a full plan, elevation and section from the same house in our guide to architectural drawings.

IFC file type and format versions

"IFC file" covers several schema versions and a few file encodings. The version matters much more than the encoding: it decides which programs can read the file at all.

IFC4.1 and IFC4.2 were interim releases on the way to 4.3 and have been withdrawn, so if a tool offers them, skip them.

Inside each version, a Model View Definition (MVD) says which part of the schema a particular exchange should contain. For IFC2x3 that is almost always Coordination View 2.0. IFC4 replaced it with the Reference View, for one-way coordination where you send change requests back to the author, and the Design Transfer View, for handing over a model the receiver will keep editing. When someone says "send me IFC", the useful follow-up question is "which version and which view?"

The file extension tells you the encoding:

Why IFC files get so big: two of our exports compared

IFC has two very different ways to store a shape. An extrusion says "take this 2D outline and push it up 2.7 metres": a few lines for a whole wall. A mesh lists every triangle. Rectangular buildings export as extrusions. Curved facades, domes and anything the exporting program cannot describe parametrically end up as meshes, and that is where file size goes.

We measured this on two models our engine produced this week, reading every entity with IfcOpenShell 0.9:

The house is built from extrusions; the office is mostly triangles. Same exporter, same schema, 30 times the file size.

Planters, curved slab edges and fins: the kind of facade that most often leaves an exporter as triangles rather than extrusions, and makes the IFC heavy. Reference: BIM Portfolio by Dheekshika Mahesh on Behance.

The practical lesson: a big IFC file is rarely "a lot of building". It is usually a few complicated shapes stored as triangles. If a model is too heavy to email, zip it first, and if it is still too heavy, look at which elements are meshes before you start deleting rooms.

How to open an IFC file

You do not need Revit or Archicad to look at an IFC file. These are the tools worth knowing, checked against each vendor's own pages in October 2026:

A school BIM model in a styled 3D view. A free IFC viewer shows the same elements without the styling, and lets you click each one to read its class and properties. Reference: School Project, KAITECH BIM Diploma by Mohamed Fayed on Behance.

If you only need to look at a model someone sent you, Open IFC Viewer is the one we would install first: free, local (nothing uploaded anywhere) and it reads every schema version in the table above. If you also need to fix something, go straight to Bonsai.

How to open an IFC file in Revit

Revit offers two routes, and picking the wrong one causes most "my IFC came in wrong" threads:

1. File > Open > IFC creates a brand new Revit model from the IFC, using your default template. Use it when you want to keep working on the model in Revit.
2. Insert > Link IFC keeps the IFC as a reference inside your existing project. Revit converts it into an intermediate model and links that, so it reloads when the consultant sends a new version. Since Revit 2024.1 a new link processor is the default, with better geometry at some cost in speed.

A villa modelled for a working drawing set. Opened from IFC in Revit, a model like this comes in as walls, roofs and windows, but not as the families and constraints it was built with. Reference: LB Villa, architectural working drawings by Mohamed Fayed on Behance.

Either way, Revit writes a log file next to the IFC, named like model.ifc.log. When elements go missing, read that log before blaming the file.

Can you edit an IFC file?

Yes, with the right tool. There are three honest levels:

• Native IFC editors such as Bonsai and FreeCAD 1.0 change the IFC itself and keep GlobalIds intact, so your edits do not break the receiver's issue tracking.
• Scripting with IfcOpenShell, the open-source library under Bonsai and under our own engine. This is how we produced every number in this article:

import collections, ifcopenshell

model = ifcopenshell.open("model.ifc")
print(model.schema)                                   # IFC4
print(len(list(model)))                               # every entity in the file
print(collections.Counter(e.is_a() for e in model.by_type("IfcProduct")))
print(len(model.by_type("IfcPropertySet")))           # 0 in our exports, see below

• Import and re-export through Revit or Archicad. This works, but it is a translation, not an edit: the output is a new IFC written by a different exporter, often with new GlobalIds and different geometry.

If you have never done the import route, watch it once before your first project that depends on it. Tekla's own introduction, from the vendor's official channel, covers the three steps you meet when a consultant sends you an IFC: importing it as a reference model, filtering it down to the parts you need, and converting IFC objects into native ones. It is shown in Tekla Structures, but Revit and Archicad follow the same logic under different menu names.

Introduction to Working with IFC Files (Tekla Software, 16:50)

Introduction to Working with IFC Files, by Tekla Software on YouTube, 16 minutes 50 seconds. The player only loads when you press play.

Opening the file in a text editor is possible, since it is plain text, but treat it as read-only. Changing a name is safe; deleting a line that other lines reference breaks the model in ways most viewers will not explain.

How to check an IFC file before you send it: our own audit

Here is the uncomfortable part. When we ran the script above on our own exports, the geometry and spatial structure were fine, and the data was thin. This is the same audit we would run on anyone's file:

None of these stop the file opening, and that is exactly the problem: a viewer shows a perfect building, and the structural engineer receives walls that do not say whether they are load-bearing. We are publishing the table as it is rather than waiting until it looks better, and we will update it whenever the exporter changes.

For your own files, the five checks that catch most problems:

1. Schema and view. Read FILE_SCHEMA in the header and confirm it with the receiver.
2. Storeys. Every element should sit on a storey, and storey elevations should match the drawings.
3. Proxies. Count IfcBuildingElementProxy. A handful is normal; dozens means the exporter did not know what things were.
4. Properties. Open three random walls in a free viewer and look for Pset_WallCommon. If it is empty, so is every wall.
5. Requirements. If your client has published an IDS file (Information Delivery Specification, a buildingSMART standard since June 2024), run it in a checker such as Open IFC Viewer before sending. It turns "the model is incomplete" into a list of exactly which objects fail which rule.

Is IFC good enough to replace native formats?

Not yet, and anyone who says it is has not round-tripped a model. IFC is excellent at what it was designed for: handing over a model so that someone else can see it, coordinate against it, check it and take quantities from it, in any software, decades from now. It is weak at the one thing native formats do best, which is carrying the design intent: the constraints, families and parametric rules that let you change a wall type and have every wall update.

The same school project as the blue model above, rendered. The render is for people; the IFC is what other software receives. Reference: School Project, KAITECH BIM Diploma by Mohamed Fayed on Behance.

So use it the way most practices do. Design in whatever tool you like, keep the native file as the master, and treat IFC as the published, checkable version of the model. The quality of that published version is entirely up to the exporter and the person pressing export, which is why the checks above matter more than the choice of BIM program.

Sources

• buildingSMART International, IFC 4.3 approved as a final standard (ISO 16739-1:2024).
• Industry Foundation Classes, Wikipedia: history, version list and file encodings (ISO 10303-21 and 10303-28).
• buildingSMART, Information Delivery Specification (IDS): approved as a final standard in June 2024.
• Graphisoft Archicad Help, Model View Definitions: IFC4 Reference View and Design Transfer View.
• Autodesk Revit Help, Link an IFC File and Open an IFC File.
• Solibri Help, Solibri Anywhere availability and next steps.
• FreeCAD Wiki, Native IFC.