Finding the right contractor to build your dream house is one of the most critical steps in your journey. Once your dream design is complete—essentially serving as a handbook for what needs to be built—the next big task is to find the team to bring it to life.

Tendering is largely a numbers game. You gather construction cost estimates, compare them, and use them as one of your primary decision-making tools. While other factors like reputation and communication skills are also important, they often take a backseat to cost considerations.

So, how can you leverage the power of BIM to make these estimates as accurate as possible? Let’s break it down into two key processes.

The decisions made during the design phase—such as the size of the building, choice of materials, and level of sophistication—have the most significant impact on construction costs. The clearer the design information, the more accurate the estimates will be.

In many of my articles, I’ve demonstrated how BIM can not only improve design quality and reduce unexpected errors but also enhance the precision of cost estimates. If you’ve used BIM to develop your design and extract quantities, this transparency will improve the accuracy of the proposals you receive from contractors.

However, it’s essential to recognize that not everything is usually modeled. If you provide quantities solely based on the model, contractors may later request additional payments for items that weren’t accounted for in the initial estimates.

To mitigate this, I recommend asking contractors to make their own calculations. Compare their estimates to the quantities you’ve extracted from your models. This dual approach helps you identify overlooked items or spot potential overestimations by contractors, resulting in a more balanced and accurate understanding of costs.

The tender process involves submitting your design to contractors for cost estimation. While larger projects increasingly see contractors utilizing models for estimation, this capability remains rare in small residential housing projects. Nonetheless, you should include your BIM models in the tender document package in case contractors have the tools to use them.

Even if contractors aren’t using BIM models, there are simple ways to improve the clarity of your design:

Include 3D Images:

Providing 3D visuals of specific design elements, can significantly enhance understanding. I’ve used this approach with contractors, and it resulted in better alignment on expectations and more accurate estimates.

One of the 3D images I used in the pavement tender process

Share Links to Interactive 3D Models:

Online tools, such as Autodesk Viewer, allow you to share and explore models directly in a web browser. This method provides contractors with a much clearer picture of your design. I’ve used this strategy during tenders for various works—MEP, interiors, etc.—and contractors consistently reported that it helped them grasp the scope and details of the project.

Check out an example model here: https://autode.sk/4gY9asn

And learn how to use Autodesk Viewer in my Free Guide.

When conducting a private tender, there’s a key difference from public tenders: the personal interaction. Think of the tendering process as a job interview. You’ll be working with the contractor for months, so it’s vital to assess whether communication is clear and easy from the start.

Don’t rely solely on digital documents. Have a conversation with the contractor, gauge their responsiveness, and ask questions. This step is as important as comparing estimates.

Finally, always make sure you have multiple options. Comparing several contractors not only gives you leverage but also ensures you select the best fit for your project.

By combining the strengths of BIM and effective tendering practices, you can gain better control over your construction costs while ensuring smoother collaboration with your chosen contractor.