What is IFC, the main ingredient of openBIM?

The birth of the IFC format

In 1996 11 partners created the IAI (International Alliance of Interoperability) which became buildingSMART International - bSI in 2008.

The objective was to enhance interoperability during the complete lifecycle of a built asset by:

  • Being neutral and open
  • Addressing all the stakeholders collaboration needs in the construction sector
  • Providing open standards

The first standard developed by BSI has now become an ISO Standard: ISO 16739-1:2018 Industry Foundation Classes (IFC) for data sharing in the construction and facility management industries - Part 1: Data schema.

At first, dedicated to buildings, IFC is in constant improvement and now addresses the whole construction sector with the addition of bridges and soon to come rails, roads, tunnels…

The IFC standard is the basis of the BIM ecosystem triangle from BSI (Data, Process, and Terms).

The BIM ecosystem triangle from bSI (Data, Process, and Terms)
The BIM ecosystem triangle from bSI (Data, Process, and Terms)


The definition of IFC

Formally, IFC are both a conceptual data schema and an exchange file format structure.

The conceptual data schema formalism is derived from STEP (Standard for the Exchange of Product Data Model - ISO 10303) and specified in EXPRESS data specification language. An XML schema generated from the EXPRESS schema is also provided.

An IFC file can be exchanged as .ifc, .ifcxml, .ifczip(compressed file).

The object model is composed of objects - named entities (construction elements and containers elements) and relationships describing the interactions between the objects (for example the relationship IfcRelConnectsElements can be used to express the connexion between 2 walls). The current IFC version (IFC 4.2) is composed of 816 entities.

Of course, IFC are not describing only geometry but much more than that. Here we are talking about semantics, in a BIM process, we are not only exchanging geometry but also data. Right now, information attached to an object is described in Property Sets. A Property Set is the placeholder where to defined properties can be attached to any entity within the IFC model. The current IFC version contains 415 Property Sets. As all properties defining construction industry concepts worldwide cannot be defined in the IFC standard, a data dictionary such as the bSDD is more and more used to settle a single source of truth. This will be explored in more detail in another article dedicated to semantics.

What does an IFC file contain?

When receiving an IFC file, the common way to check the content of the Building Information Model is to use an IFC viewer. An IFC viewer can only read IFC openBIM files whereas some BIM viewers are able to read other proprietary BIM formats such as Revit, Archicad, Tekla…

The viewer will allow seeing the geometry but also all the information attached to each object composing the model. It is thus easy to verify:

  • The geometry, shapes, connections
  • the values of properties dedicated to thermal calculations
  • the values of properties dedicated to structural calculations
  • all the quantities needed to cost estimation
  • all the properties dedicated to environmental impact calculations
IFC file in Bimsync
IFC file in Bimsync


Why use IFC in a construction project?


By using an open and standardized format, all the stakeholders involved in a construction project are able to describe and structure the information in a common way.

In a construction process, all the actors will use and enrich the information relative to the project in their own specific tools. Without a standardized way of sharing the information (ie using proprietary formats), the data has been entered manually in all those tools, and many times; thus there is no way of sharing this information during the whole lifecycle of a built asset.

Nowadays, the use of a Common Data Environment (CDE) in a construction project has become widespread. Using a platform IFC compliant allows all actors to share information in a common, open and standardized way; whatever is the software used to author, read, enrich content, if it is IFC compliant there is nothing more than uploading/downloading IFC files to access and use the information.

Another huge interest in using the IFC format is that users are not dependent on the versioning of software with new file formats for almost every version. When opening a file 10 years later, a software compliant with the IFC standard will still be able to understand the information.

Finally and maybe even more important, IFC are in constant evolution to address the needs of the market and all the improvements are made under the control of construction professionals.

As openness is one of the pillar values of Catenda, we have chosen to use IFC as the format supported by Bimsync.


IFC in Open BIM environment
IFC in Open BIM environment


Is the market ready for openBIM and IFC?

Most of the common software used in the construction sector are already IFC compliant.

buildingSMART International provides a certification process for software vendors, the list of certified software can be accessed at https://www.buildingsmart.org/compliance/software-certification/certified-software/

buildingSMART also provides a professional certification program to enable learning organizations to educate and certify individuals according to a recognized global learning framework. With this Program, buildingSMART provides a global benchmark for openBIM competency assessment. More to learn at https://education.buildingsmart.org/


By Frédéric Grand, Catenda

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