How to Extract Quantities from Poor BIM Models

Extracting quantities from a well-structured BIM model can be straightforward and simple. But let's face it - how often is the model well-structured and complete, especially in the early phases of the project? When the model is incomplete, inconsistent, or contains poor data, the process becomes more challenging. Here’s a step-by-step guide on how to deal with subpar models while ensuring your quantity takeoff is still accurate.

1. Understand What Makes the BIM Model "Poor"

The first step is to assess why the model is difficult to work with. Is it missing key data, such as material properties or classification information? Or is the geometry incomplete, inaccurate, or unsuitable for quantity takeoff? Understanding this distinction will help you plan the rest of the process.

2. Run a Clash Detection Check

Clashes in the model can lead to double-counting or missed quantities. Use a clash detection tool like Solibri Office or BIMCollab Zoom to ensure the model geometry doesn’t overlap in ways that distort your takeoff. This step saves time and improves accuracy by identifying problem areas early.

3. Verify the Information

Apart from geometry, the model’s information may also be faulty. Use information-checking tools such as Solibri Office or BIMCollab Zoom to assess whether the metadata is reliable. If needed, use Sparkel to adjust or fill in missing information without touching the original model.

4. Start With the End Result in Mind

Before diving into extraction, consider what the perfect quantity export should look like. Define the desired outcome and work backward from there. In Sparkel, for example, you can set up takeoffs line by line, ensuring that you know exactly how the end result will look. If you have company standards, these should also be created as templates, so that you don't have to do this from scratch for every project. This clarity helps you focus on which parts of the model need tweaking or additional input.

5. Differentiate Between Estimation and Execution

Are you extracting quantities for a static estimation or for an ongoing project where revisions are frequent? If it’s for estimation, you could tweak the model in software like Revit or Archicad to match your needs. However, if it’s for project execution, where revisions are expected, be cautious. You don’t want to reapply your changes every time a new version arrives. Sparkel can help you manage this by preserving changes and additions without altering the original model.

6. Handle Missing or Incomplete Geometry

When geometry is lacking or incorrect, don’t give up. Tools like Sparkel allow you to define areas or elements that the model doesn’t capture well. This way, even if the model’s geometry is flawed, you can still extract meaningful quantities. There are also a lot of quantities that never have dedicated geometry, like formwork or pouring phases, so make sure you are able to extract these types of quantities anyway.

7. Extract Specific Parts of the Geometry

Sometimes, you don’t need the whole element, but only a specific part. Sparkel lets you isolate and work with partitions of main geometries through its Shape functionality. This flexibility is crucial when the model doesn’t align perfectly with your needs.

8. Bridge the Gaps

After identifying missing or incorrect data, the next step is to fill those gaps. Sparkel shines here as it allows you to tweak both geometry and data, and importantly, it doesn’t modify the underlying model. This approach is especially beneficial when managing revisions since your changes will persist across updates. This means that you quantity takeoffs will consist of a mix between original model information, as well as your enriched information.

9. Work Through the Required Quantities

With the geometry and information improved, work systematically through each item you need quantities for. Sparkel helps you manage this process, letting you link elements to items in a way that ensures accuracy and consistency across the board. Sparkel will also visually display which elements in the model hasn't been linked to any items yet.

10. Don’t Overlook 2D Takeoff

If the BIM model is too complex or the quantities you need are difficult to extract, there’s no harm in going back to basics with 2D takeoff. For example, plan areas are often easier and quicker to measure in 2D. Sparkel allows you to integrate both BIM and 2D takeoff within the same environment, ensuring you get the most accurate results with maximum flexibility.

Conclusion

While extracting quantities from poor BIM models is undoubtedly challenging, it’s far from impossible. By carefully assessing the model’s limitations, working backward from the desired output, and using flexible tools like Sparkel, you can streamline the process and still achieve accurate results. And when things get too tricky, remember that combining BIM with 2D takeoff can sometimes be the most effective approach.