# IFC Files: How to Open a BIM Model Online and What You Will See

IFC is the open buildingSMART format for BIM models. Learn how to open an .ifc or .ifczip file online, which building elements are shown, how units are read and what a quick viewer leaves out.

IFC (Industry Foundation Classes) is the open data model that buildingSMART publishes for building information modelling and that ISO standardises as ISO 16739. Revit, Archicad, Tekla, Allplan, Vectorworks and most structural and MEP tools export it, which makes it the usual way to hand a building model to someone who does not use the same BIM program. An `.ifc` file is plain text in the same Part 21 encoding as STEP; `.ifczip` is the same file in a ZIP archive.

You can open both in [the CADProps workspace](https://www.cadprops.com/workspace/index.md). The building elements are shown as an approximate triangle mesh, one part per element and grouped by storey, so you can hide walls to look inside, check the overall size, measure between points and export STL, OBJ, GLB, glTF, 3MF or mesh STEP after sign-in. It is a fast geometry viewer for the file, not a BIM authoring tool: the property sets, quantities and relationships in the model are not shown.

## What is shown

IFC describes each wall, slab, column, door or fitting as a product with a placement and one or more shape representations. CADProps reads the common ways those shapes are written:

- extrusions of rectangles, circles and simple closed outlines, which covers most walls, slabs, beams and columns;
- faceted B-Reps and triangle or polygon face sets, which many exporters use for furniture, fittings and anything irregular;
- mapped items, so a door or chair defined once and placed many times appears at every placement;
- the local placement chain, so each element sits where its storey and parent put it.

Each element appears as a part named after its IFC class and name, such as `IfcWall house - outer wall`, under its storey. Constant surface colours are kept when the file defines them.

## What is left out

Some IFC geometry needs real solid modelling to evaluate, and a quick viewer leaves it out instead of guessing:

- **Openings are not cut.** Door and window openings are separate elements in IFC that are subtracted from the wall. CADProps does not subtract them, so walls appear solid; the doors and windows themselves are still shown.
- Spaces and spatial zones are hidden, because their room volumes would cover the building.
- Boolean and clipping results, curved advanced B-Reps, swept curves, faces with holes and unsupported profiles are omitted. The model is then marked incomplete and the warning lists what was skipped.
- Geographic map conversion is not applied; the model is shown in its local engineering coordinates. Markers that some files place at the survey point can therefore appear far from the building.

Very large models can exceed the viewer's triangle or element budget and are rejected rather than shown in part. For those, export a smaller selection, for example one storey or one discipline.

## Units

IFC files state their length unit in the project's unit assignment, often millimetres for architectural models and metres for civil or site models. CADProps reads that declaration and converts to millimetres, so the scale is marked verified. If a file has no length unit, millimetres are assumed and area, volume and mass are turned off. A quick check against a known storey height or door width still helps; see [the scale factor guide](https://www.cadprops.com/guides/cad-model-wrong-scale-25-4/index.md) if a model looks a thousand times too big or small.

Area and volume, where shown, are summed over the displayed elements. Overlaps are not subtracted and openings are not removed, so do not use them as quantities for costing. The [format matrix](https://www.cadprops.com/supported-formats/index.md) lists every input and its limits.

## Related reading

- [STEP File Scale Wrong by 25.4? Fix Inch and mm Units](https://www.cadprops.com/guides/cad-model-wrong-scale-25-4/index.md)
- [CAD Tessellation: When a Solid Becomes a Triangle Mesh](https://www.cadprops.com/guides/cad-tessellation/index.md)
- [IGES File (.igs, .iges): What It Is and How to Open It](https://www.cadprops.com/guides/iges-file-what-it-is-how-to-open/index.md)
- [Open a Rhino 3DM File Without Rhino](https://www.cadprops.com/guides/open-3dm-without-rhino/index.md)
- [Open CAD Files on Mac: STEP Viewers and Format Options](https://www.cadprops.com/guides/open-cad-files-on-mac/index.md)
- [X3D and X3DV Files: What They Are and How to Open Them Online](https://www.cadprops.com/guides/open-x3d-file-online/index.md)
- [STEP AP203 vs AP214 vs AP242: Which Protocol to Export](https://www.cadprops.com/guides/step-ap203-ap214-ap242/index.md)
- [Watertight Mesh: When an STL Can Have a Volume](https://www.cadprops.com/guides/watertight-cad-mesh/index.md)

Original article: https://www.cadprops.com/guides/open-ifc-file-online/

HTML page: https://www.cadprops.com/guides/open-ifc-file-online/