BIM Buster - BIM delivers costs with the press of a button
Let's bust the BIM marketing dream of 5D-BIM and how easy it is to get building costs by pressing a few buttons. And learn how you can get there.
Building cost calculation is the topic most clients are very interested in, and most planners don't like. According to the SIA phase models, cost calculations should be done at the end of the different phases in Switzerland. The precision at the beginning is 25%. And I guess in other countries, it’s similar.
Just imagine this for a private client. Building his house is the most significant investment of his life. Your new house costs 500K, or 600 K. 100K, which is a vast difference that ultimately decides the feasibility of the endeavor.
So now, BIM marketing says, with 5D-BIM, everything is better! The architect just models, and the building costs are a byproduct. I always dreamt of a Sim City-like counter. For every line you draw, the count goes up.
I had a contract with a developer, and the management was very interested in BIM and this Sim City-style cost calculation. The two quantity surveyors of this group were very critical and, in the beginning, almost hostile toward me (the supposed devil who brings change). So, this topic of 5-D BIM is emotional.
Of course, management loves the feeling of control and not having to wait for something crucial for decision-making. So, they want to believe the BIM marketing message.
On the other hand, the quantity surveyors know about the efforts of:
Getting the right base quantities.
Knowing relevant unit prices.
The uncertainty of the market.
The importance of location.
The difference between cost, price, and value.
So they were critical, and my job was to tell management, yes, you can get there, but
It has many consequences for how your teams currently work and, even more importantly, how they work together.
Without the buy-in of the quantity surveyors who have the domain, you won't get any results.
The quantity surveyors, I had to tell:
Yes, your know-how is not replaceable (Or the effort in data prep to do so is humongous and, for a single planning organization, not feasible).
Yes, the others see it as too simple.
By approaching more structured cost calculations, we can get closer to this goal or at least reduce your workload (a massive issue for them). This will allow you to delegate part of the job and have more of a quality assurance (manager) position.
So, it involved changing how people work and how they define themselves. I failed to create the necessary change in a meaningful timeframe in this organization.
Do you see some parallels to your organization?
On the other hand, this story gives some hints about what's necessary to get to the goal:
We need to find a structured way of getting quantities from planning to the person having the costing know-how. Without this, the quantity takeoff would take too long.
We need to calculate meaningful unit prices that work with the reference quantities we receive. BIM modelers often get this wrong and believe the more detailed the model, the easier it is to calculate costs. Usually, data consistency is more important.
We need a tool that allows the quantity surveyor to combine these elements. Usually, this is not the BIM tool, as it is focused on modeling and not data management, and quantity surveyors often have skills other than those used in these tools.
How to achieve structured quantities
It's quickly said. All modelers need to work religiously according to the same standard. In terms of:
How to model geometry
How to name elements
Which attributes to attach to the elements
How to fill the attributes with which values
The list is in order of priorities, but the automated quantity takeoff fails if only one aspect is missing.
There are many moving parts. Do you know an office that consistently uses the same layers in all its projects?
No? How do you expect that the same people suddenly manage to work even more structuredly and standardize geometry, naming, other attributes, and values? The step is too big, leading to frustration and failed BIM implementations or at least to more manual work.
The answer to this issue is twofold.
First, we need to make the modeling standard as simple and natural as possible for the planning team, but not as simple. The simplest way I found so far is:
Model as you want and need to do your job. Make sure you model the spaces, the emptiness between the walls and slabs with a volume.
Export these spaces as IfcSpace and name them according to their use in the Attribut IfcSpace.LongName.
When you model Windows and Doors, use the defined tools in your BIM solution. This guarantees that they can be exported as IfcWindow and IfcDoor.
That's it. Depending on how you count, there are only three rules modelers must follow. Even more importantly, these rules are close to the modeler's interests. Spaces are usually used for area calculations, and windows and doors are important architectural elements.
Secondly, we use automation to get more out of this. Whit this IFC file containing Spaces, windows, and doors, you can use the abstractBIM service. It calculates new consistent models based on the provided input. The logic is that an interior wall is a waḷl between two spaces, so when you know the spaces, the computer can calculate the walls.
You get an Excel file with all the quantities and a new consistent BIM file with walls, slabs, surfaces, rooms, windows, and doors back.
You can build your unit cost database and cost calculations template based on this. We will explore both topics in another article.
The important takeaway is:
As a quantity surveyor, start talking to the modelers (architects) so that they can give you models according to your needs.
Do not return to business as usual, its wasting your time.
Accept and stop grumbling about incompetent architects.
Ask them to deliver these minimal IFC models, get 80% of the work done, and focus your effort on the rest that is not easily automated.
(If you want to, you can find something else to grumble).
Give it a try at abstractBIM.com or drop a comment for further discussions.