How Much Cash Did BIM Save Me When Building My House?

February 6, 2024 at 7:00 am, No comments

Calculating the benefits of using Building Information Modelling (BIM) in a project is notoriously difficult. I will explain why in a bit. However, among those who have successfully adopted BIM, there is a clear consensus that it allows for savings on construction costs for both big and small buildings.

I completely agree, but that is not the only benefit. The satisfaction of using the building after it is built is something that you cannot estimate financially. However, being happy about the result every day is something that proves the value of BIM even more.

In this post, I will write about the financial savings for my house during the various stages. I did not calculate in a scientific way, and I am not sure if it is even possible due to the aforementioned reasons. Nevertheless, I give my best estimate at the end of the post.

The Most Common Types of Errors

Looking back at the project of my house, I can identify the following four groups of problems that affected or could affect the cost if not found early:

Design errors (when 3D models are created, these could also be modeling errors).
BOQ (having models does not guarantee more precise BOQs, as in many cases, they are produced not from models or the models are of poor quality).
Construction errors - something is not built according to design and has negative effects, or something is built of poor quality.
Well-being - the design is as agreed with the client, and the building is constructed according to the design, but when the building is used, you realize that you made an error, for example, in the layout.

Major Errors During The Construction of My Home and How BIM Helped

I have split the errors according to the previously mentioned principles because each of these phases has a very high impact on cost and well-being.

Design Phase

The design phase is the best time to identify and resolve errors because it costs almost nothing. However, it is not easy due to the sophistication of the information.

If you have no construction experience, you will probably be looking at issues related to comfort or appearance. But there are others that can be very costly as well - constructability (if the solution can be built), cost to build a solution, engineering aspects like whether there is enough space for MEP equipment and what type is needed.

I tried to address this by involving as many professionals in the design as possible to provide their feedback and by utilizing BIM.

Here are some examples of errors that were found during the design phase of my house, and fixing them later would incur significant costs.

Missing Opening For Ducts

In the late stages of the design, I showed the structural engineer the size of the opening needed for ducts. Though she was informed earlier about the fact, she did not think the sizes would be so large, and it turned out that the structural part had to be redesigned quite significantly. You would not be able to simply create an opening of such size during construction. The result was a completely redesigned structural scheme because the opening was linked to the whole metal framing system that was there for the stair opening. The cost of finding such an error during construction would be enormous.

Kitchen Window Elevation

Because my wife and I are quite tall, we wanted the kitchen countertops higher than usual (100cm instead of 90cm). There are two windows in the kitchen area, and at first, it was overlooked that they should also have a higher elevation (the standard is 90cm). It would not be possible to resolve such an issue in construction because the windows are installed much earlier than the kitchen, and there are no options to increase the height after installation.

Misalignments Between architecture and MEP

In this example, the architect placed the sink in a different place than we wanted. This error could be costly because sewage pipes have a particular way of installation and they are not small. Maybe it could be resolved, but this place is densely packed with other equipment, and it would probably be difficult.

There were many other issues found and resolved during the design phase, for example, inconsistencies between architectural and structural disciplines. Without BIM or experienced people looking at the design early, there would be a significant cost impact during the construction and use phases.

BOQ Development

The BOQ was done by an estimator, and here I confess I made the error of not checking it more thoroughly and comparing the various quantities with BIM. The BOQ had several costly errors, both underestimations, and overestimations, here are the most significant:

The Underestimates:

Square meters of one of the smaller roofs were not included in the BOQ resulting in additional costs during construction.
The length of electrical cables was heavily underestimated.

The Overestimates:

During construction, I started comparing most of the BOQ with BIM and could save money on:

Façade materials (Quantities extracted from BIM were smaller than in the BOQ).
Finish areas extracted from BIM were much more precise than in the BOQ.

Construction

Because so many errors were resolved during the previous phases, the construction process was quite smooth. The errors that were found and resolved were linked to several factors. One example is that the pavement was designed without the correct slope (was not modelled in 3D), and the structural engineer missed that the columns under the canopy had to have different lengths.

Other errors were linked to changes from the initial design - like MEP routing changes or windows installed in a much too moist environment.

Nevertheless all these errors were successfully resolved with minor or no additional cost.

Well-being

I have been living in my home for almost 2 years at the time of writing this post, and my honest conclusion is that there are absolutely no major things we would have done differently in terms of everyday comfort and appearance. Yes, there are some minor things - one additional light switch would be more comfortable or a slightly different paint tone in technical rooms, but if we wanted, these could be resolved easily and without a large cost.

Conclusion

The cost of construction errors depends on many factors:

When the error is identified - the faster, the less costly to resolve.
Error type: e.g., major structural or design error or a minor error that affects only cosmetics.
The cost to solve the error during construction: not all issues that are missed during the design are costly to resolve during construction. This also means that not all issues should be solved during the design phase because it would be, for example, too time-consuming.
etc.

Using BIM for design development, interior planning, communication, clash detection, and estimations, in my opinion, has significantly reduced the number of errors during the construction phase. But the most important and also costly errors are the ones that affect the use of the building, and for now, it seems that those have been avoided almost completely.

My rough estimate is that the savings during the construction phase were around 10-20% of the total construction budget. However, this does not include the savings and improvements to well-being during the use of the building, which, if calculated for the whole life cycle, can be much more than during construction. In my case, I saw enough proof of the benefits of using BIM for small buildings to recommend it to everybody.