How to detect changes in IFC models

If you are a professional in the construction industry, you surely know how important it is to monitor changes made to a BIM project. However, tracking all the variations over time can become a very complicated task. Especially if the project involves multiple professionals and numerous versions of a 3D model.

Fortunately, there is a solution: to compare 3D models.

You can try now and for free, this tool which allows you to compare accurately, identifying difference of your 3D model versions. In this article I’ll explain in detail how to use it, showing you with a step by step video.

How to detect changes in project IFC models

Why it is important to detect changes between versions of an IFC model

The comparison between versions of an IFC model, the “model comparison”, is not just a control activity, but a true process of quality management and evolution of the digital project. Every update, revision, or variant involves potential changes in geometry, properties, or the structure of IFC data. But let’s look at everything in more detail.

Quality control (QA/QC) in IFC BIM models

Quality control (QA/QC) is one of the main reasons why detecting changes in IFC models is so important. This process allows you to:

• verify geometric consistency, for example, if structural elements have been moved, resized, or deleted;
• check the completeness of information, such as missing properties, changes to material parameters, or energy performance;
• ensure compliance with corporate and regulatory BIM standards, such as the structure of the Property Set, correct IFC classification, and uniformity of naming conventions.

The automation of this control, made possible by BIM validation platforms or specific tools for IFC comparison, reduces the risk of human errors and improves the overall quality of the model, ensuring that every revision is verified before being shared or used in the subsequent phases of the project.

Coordination between disciplines and project variants

Each discipline works on its own models, often updated at different times, and a seemingly minor change (such as moving a column or varying the layout of a duct) can generate interferences or require immediate adjustments.

The comparison between IFC versions allows you to:

• highlight interferences between disciplines, facilitating the work of the BIM Coordinator;
• manage project variants in a controlled manner, precisely tracking what has changed, when, and why;
• support the decision-making process, allowing the client or project manager to assess the technical and economic impact of changes.

This approach increases transparency in the information flow and reduces the time needed for model reviews, improving the quality of collaboration between distributed teams or with different software.

Traceability of revisions in the model’s lifecycle

Every IFC model evolves over time, reflecting the progress of the design, construction, and management phases of the work. Traceability of revisions allows understanding how the model has developed, who introduced certain changes, and for what purposes. This aspect is particularly relevant in BIM processes based on standards such as ISO 19650, which require rigorous management of versions and revisions.

Detecting changes between IFC versions means being able to build a digital history of the project, useful for:

• conducting technical audits or compliance checks;
• documenting the evolution of the model for contractual or insurance purposes;
• simplifying the transfer of information between the design, construction, and management phases (As-Built and Facility Management).

Impacts of different IFC versions (IFC2x3, IFC4, IFC4.3) on interoperability

Each version (IFC2x3, IFC4, IFC4.3) presents significant differences that can influence the outcome of the comparison between models.

• IFC2x3, still widely used, offers a solid foundation for compatibility but has limitations in managing Property Sets and representing complex geometries.
• IFC4 introduces substantial improvements in support for MEP entities, material management, and defining relationships between objects, ensuring greater accuracy in detecting changes.
• IFC4.3, designed for the infrastructure and civil sector, further expands semantic and geometric coverage but requires updated software to ensure reliable comparison.

During the comparison between models, it is essential to consider the IFC version used: an analysis between files of different versions can lead to false positives or negatives, due to differences in data structure rather than actual design changes. A deep understanding of IFC specifications and the choice of tools compatible with multiple versions are therefore fundamental requirements for a correct and interoperable analysis.

Comparison between two IFC models

Step-by-step procedure to compare two IFC models online

Comparing two versions of an IFC model is now an operation that can be done directly online, thanks to cloud BIM platforms that allow for visual and informative analyses without the need for complex desktop software. This procedure is essential for Quality Assurance, interdisciplinary coordination, and revision management.

Let’s take a closer look at the main steps of a typical procedure for comparing two IFC models online.

Uploading the IFC models

The first step is to upload the two versions of the IFC model into a 3D model comparator.

During this phase, it is advisable to:

• ensure that both files are correctly exported from the authoring software (Revit, Archicad, Edificius, etc.) and comply with the same IFC version (IFC2x3, IFC4, etc.);
• clearly name the files following a standard convention (e.g., Project_School_v01.ifc and Project_School_v02.ifc) to avoid ambiguity during the comparison;
• if possible, attach metadata related to the revision or discipline (architectural, structural, MEP).

Aligning the models

Once the files are uploaded, the next step is the alignment of the models, positioning them on the same coordinate system.

This step is crucial: even a small deviation in the origin or scale can compromise the comparison results.

In advanced software, alignment can be performed automatically based on the IFC coordinates, or manually by selecting common reference points (such as axes or structural anchor points).

The goal is to achieve a perfect overlay between the two models, a necessary condition for an accurate analysis of the differences.

Executing the comparison

Once aligned, the model comparison function is initiated to detect changes in the IFC models.

The system analyzes the geometry and information (property set, materials, classifications, relationships) contained in each model, returning a detailed list of variations.

The comparison can be:

• Geometric, highlighting objects modified in shape, position, or size;
• Informative, indicating changes to properties, technical parameters, or classification codes.

Online platforms display the results through differentiated color coding (for example: green for added elements, red for removed, yellow for modified, gray for unchanged), allowing for immediate analysis even for users who are not experts in 3D modeling.

Filtering and analyzing the differences

After the comparison, it is useful to filter the results by category, discipline, or level of detail.

For example, one might decide to analyze only the changes related to electrical systems or load-bearing structures.

Cloud platforms offer tools to:

• sort changes by type (Added, Removed, Changed, Unchanged);
• visually isolate the affected parts;
• display pre- and post-revision properties for each selected element.

This type of analysis allows BIM Coordinators to validate changes before approving or integrating them into the federated model.

Documentation and sharing of results

At the end of the comparison, the results can be exported in the form of:

• reports in PDF or CSV format, with a list of changes and their properties;
• BCF files (BIM Collaboration Format), which allow linking each change to a specific issue and sharing it with various project teams.

Thanks to this integration, the comparison process naturally fits into the revision management cycle and the traceability of coordination activities.

Review and validation

The comparison between IFC models does not conclude with merely identifying the differences: it is necessary to proceed with a technical validation.

The design team or BIM Manager must analyze whether the changes are consistent with the project specifications, regulatory constraints, and client requests.

At this stage, the comparison platform becomes a decision-support tool, allowing for the approval, rejection, or commenting on each individual change, thus ensuring precise control over the evolution of the BIM model.

Comparison between two versions of the IFC model with visualization filters

How to read and interpret the differences overlay in the IFC model

The comparison between versions of an IFC model visually translates into an overlay: a superimposition of two 3D models that allows for the immediate identification of geometric and informational differences. This representation, typically color-coded, is an essential tool for analyzing the evolution of the project, understanding the impact of changes, and validating their correctness.

Correctly interpreting the overlay is a key skill for those involved in BIM coordination, as it allows for quick distinction between new, removed, modified, or unchanged elements and links each variation to a specific phase of the design process.

Added Elements (added compared to the previous version)

The Added elements are those introduced in the new version of the IFC model and not present in the previous version.

In the 3D viewer, they are generally highlighted in green, a color that indicates the addition of new components or objects.

Some common examples of added elements include:

• new structural components (beams, columns, secondary foundations);
• architectural elements introduced following a variant (partition walls, fixtures, furnishings);
• MEP equipment or ducts added for system updates.

The analysis of these elements allows for the assessment of the impact of changes on the overall geometry, on interferences with other disciplinary models, and on the metric computation.
It is advisable to verify that each added element is correctly classified and equipped with all the Property Sets required by the company BIM standard.

Removed Elements (removed in the new version)

The Removed elements, generally represented in red, are those that were present in the previous version but have been eliminated in the subsequent revision.

The removal of an IFC object can stem from multiple reasons: design changes, structural optimizations, regulatory updates, or simple corrections of modeling errors.

Identifying and analyzing the removed elements is essential for:

• understanding the technical or design rationale for the removal;
• assessing any impacts on structural stability or systems;
• correctly updating related documents (graphic elaborations, computations, schedules).

In the case of large revisions, it is useful to generate a report with the complete list of removed elements, associating each with a BCF issue, thus maintaining traceability and justification for each variation.

Changed Elements (modified in geometry or properties)

The Changed elements, usually highlighted in yellow or orange, represent objects present in both versions of the model, but that have undergone changes in geometry, properties, or both.

The variations may concern:

• geometric parameters (position, size, orientation, volume);
• informational properties (material, strength, transmittance coefficient, classification code);
• relationships between objects, such as association with a new level, system, or zone.

This type of modification is often the most critical, as it can affect multiple design and coordination aspects.

It is good practice for the BIM Coordinator or Model Checker to analyze each variation by comparing the properties before and after the revision, ensuring that the change is consistent with the specifications and does not generate interferences.

Unchanged Elements (unchanged)

The Unchanged elements, normally displayed in gray, are those that have not undergone any modification between the two versions of the IFC model.

Although they do not require direct interventions, these objects play an important role in the overall analysis, as they constitute the stable reference against which differences are identified.

Maintaining a large proportion of unchanged elements is often indicative of good design stability and effective control of the revision process.

In some cases, however, seemingly unchanged elements may present variations that are not graphically detectable (such as differences in metadata or IFC relationships); for this reason, it is recommended to use tools that allow for both informational and geometric comparison.

IFC model and element visualisation

Geometric Differences and Informative Differences in IFC Models

The comparison between two versions of an IFC model involves not only the shapes or sizes of objects but also the enormous amount of alphanumeric information that describes them.

Understanding the distinction between geometric differences and informative differences is essential for correctly interpreting the results of the comparison and identifying any critical issues that could affect the project or the management of the BIM model.

In a professional workflow, in fact, a model can maintain the same geometry but undergo profound changes in the associated data (or, conversely, present a new spatial configuration while retaining the same information). Analyzing both types of differences ensures consistency, reliability, and traceability over time.

Geometric Differences

Geometric differences involve any variation in the shape, position, or size of an IFC element.

These changes are directly reflected in the three-dimensional representation of the model and can have significant impacts on coordination between disciplines.

Typical examples of geometric differences include:

• shifting of columns or beams that affects structural alignment;
• modifications to openings (doors, windows, voids) that alter architectural distribution;
• variations in the paths of ducts and conduits that generate new system interferences;
• updates to the terrain or elevation levels in infrastructure models.

During the analysis, these changes are generally detected through a geometric matching algorithm, which compares the coordinates and solid volumes between two versions of the model.

It is important to consider the geometric tolerance set in the comparison tool: values that are too low can signal false positives (irrelevant differences), while tolerances that are too high risk hiding real variations.

Geometric differences are often the most evident but also the most critical, as they can compromise compatibility between disciplinary models and cause construction errors if not properly verified.

Informative Differences

Informative differences, on the other hand, concern the content of the data associated with IFC objects, without necessarily involving changes to their three-dimensional representation.

These are variations in the Property Set, classification parameters, materials, or semantic relationships between objects.

Here are some practical examples of informative differences:

• updating the material of a wall (from concrete to brick blocks);
• modifying the value of a technical parameter (thermal transmittance, resistance, flow rate);
• variation of the classification code (e.g., from IfcWall to IfcWallStandardCase);
• addition or removal of custom attributes in corporate Property Sets;
• changing the ID or name of the object due to a new IFC export.

These variations, while not graphically visible, can have direct implications on quantity takeoff, energy analysis, maintenance management, or regulatory compliance.

For this reason, an effective comparison must also include the comparison of informative data, often presented in tabular form or within detailed reports automatically generated by the software.

Combined Management of Differences

In many cases, geometric and informative differences coexist: for example, a shifted column (geometric difference) may also have a modified concrete class (informative difference).

It is the responsibility of the BIM Coordinator or Model Checker to distinguish purely formal changes from those that impact the informative content, assessing the implications in terms of costs, timelines, and project quality.

The most advanced tools allow for integrated visualization: the user can select an element and simultaneously view the 3D geometric comparison and the information sheet before and after revision.

This dual reading ensures a complete understanding of the changes and facilitates the validation of the model according to corporate standards and client requirements.

Comparison of IFC model property values

FAQ on How to Detect Changes in IFC Models

Why is it important to detect changes between versions of an IFC model?

Comparing versions of an IFC model, ‘model comparison’, is not merely a control activity but a true process of quality management and the evolution of the digital project. Every update, revision, or variant involves potential changes in geometry, properties, or the structure of the IFC data. Detecting changes helps ensure the overall quality of the model and the correct traceability of the design process.

What is the role of quality control (QA/QC) in BIM IFC models?

Quality control (QA/QC) is one of the main reasons why detecting changes in IFC models is so important. This process allows for the verification of geometric consistency, checking the completeness of information, and ensuring compliance with corporate and regulatory BIM standards. Automating QA/QC through IFC comparison tools reduces the risk of human errors and ensures that each revision is validated before sharing or using it in later stages of the project.

How does comparing IFC versions improve coordination among disciplines and management of project variants?

Comparing IFC versions allows for highlighting interferences between disciplines, managing project variants in a controlled manner, and supporting the decisions of the client or project manager. Detecting changes in IFC models enables tracing what changed, when, and why, thereby reducing review times and improving collaboration among multidisciplinary teams working with different software.

Why is traceability of revisions essential in the life cycle of the IFC model?

Traceability of revisions allows for understanding the evolution of the model over time, identifying who made the changes and for what purpose. Detecting changes between IFC versions means building a digital history useful for technical audits, contractual or insurance documentation, and simplifying the transfer of information between design, construction, and management (As-Built and Facility Management).

What are the impacts of different IFC versions (IFC2x3, IFC4, IFC4.3) on interoperability?

Each IFC version presents differences that affect model comparisons. IFC2x3, still widespread, has limitations on Property Sets and complex geometries. IFC4 introduces improvements in MEP entities, material management, and relationships between objects. IFC4.3 broadens semantic and geometric coverage for the infrastructure sector. Understanding how IFC versions influence the ability to detect changes in IFC models is essential to ensure interoperability and data consistency throughout the project life cycle.

Video

In this short video, I show you how to detect changes between two IFC models with usBIM.compare. You can try the completely online 3D model comparison for free to compare and evaluate revisions of IFC files in just a few simple steps.