BIM cost estimating
BIM cost estimating uses BIM models to produce detailed BIM cost estimates automatically allowing surveyors to avoid errors and save time
If you often find yourself preparing Quantity Takeoffs from BIM models, you may also want to speed up your productivity and minimize the possibility of introducing errors. If that’s the case, you can get your hands on a 5D BIM software to produce your BoQs and cost estimates directly from your BIM models. This process is also known as BIM cost estimating.
What is BIM cost estimating? What are its benefits for the Quantity Surveyor?
In this article we’ll be taking a closer look at how BIM models can be used to produce accurate BoQs and cost estimate docs of a construction project using advanced artificial intelligence technology.
What is BIM cost estimating?
BIM cost estimating is the process by which a BIM model is used to generate an accurate estimate of the quantities and costs related to the construction of a work.
The cost assessment is also defined as the fifth dimension of BIM (5D BIM).
We know that BIM allows to associate to the 3D model all the necessary information to the entire life cycle of the work. We also know that every object of the model is not only a simple geometric entity, but contains useful data for the designer, the company and the client (dimensions, materials, technical data sheets, execution and maintenance methods, etc.).
This information also includes those relating to the costs of the works to be carried out (whether it is new construction or maintenance, restoration, renovation or even demolition of the property).
Basically, if we have the 3D BIM model of a building, just select a wall, a window or a slab to read all the data and features. The BIM model is therefore configured as a container of information that can be consulted but also implemented over time.
The information model can also be shared and managed freely with a BIM management system that allows you to view and manage IFC models generated with any BIM software.
In this way, collaborating and exchanging information with the other professionals involved becomes easy.
BIM cost estimating exploits the potential of 5D BIM software to:
- produce the project cost estimate from the BIM model automatically;
- have visual control of the computed entities directly on the 3D model;
- dynamically update the Quantity takeoff/cost estimate at each design change;
- create measurement templates to be applied to any other project.
Ultimately, obtaining the quantity takeoff directly from the BIM model rather than from the 2D drawings, implies that the measurements are generated directly from the 3D model without the possibility of error and are always consistent with the project. In addition, with each change made (for example, you choose to change the size of a window) all the documentation (plans, sections, cost estimates, time schedules, etc.) is updated seamlessly and automatically .
The time taken to process a cost estimate is greatly reduced as wells as human error.
This innovative process does not discredit the professionalism of those involved in the drafting of quantity takeoffs. It avoid repetitive and mechanical procedures to leave more time for design details, risk identification, construction phases and methods and all aspects that come into play when generating an accurate and realistic cost estimate. The fundamental attitude for those who deal with cost estimating, in fact, is not calculating quantities but precisely to define all the processes necessary for the correct execution of a work.
How is BIM used in cost estimation?
Cost estimate can be defined as the process prior to the execution of a work useful for calculating the quantities and defining the processes necessary for the execution of the work itself.
In the traditional way of designing, it is seen as a process that requires time not to mention manual and repetitive operations, which is why it is often subject to errors.
Software for quantity takeoff were already available before BIM technology. Their support was mainly related to reducing the time spent accounting quantities and ordering quantities and processes by making simple mathematical calculations.
BIM technology, on the other hand, introduces many improvements, both in terms of the calculation process itself but also in the sharing of information useful for construction. This implies, however, that the 3D BIM model is built with a high degree of detail and is consistent with the needs of developing an accurate cost estimate.
Basically, in order to use BIM in the cost estimation phase, it is necessary to:
- create the detailed BIM model of the building with the support of 3D building design software;
- use a 5D BIM software;
- choose the processes from the reference price list;
- select at least two entities directly on the BIM model to allow the 5D BIM software to automatically identify all similar entities;
- define the measurement rule (by applying predefined templates or by creating new ones).
With a 5D BIM software, you can import and view the BIM models in the IFC format, generated with any BIM authoring software.
There are advanced methods of automatic and custom selection to associate the work identified with the entities to be computed. Once processes and types of entities have been identified, simply choose the measurement rule containing the descriptive and metric information that the software will apply to calculate automatically.
Usually, measurement rules created for a single project can be saved as templates and reused in any other similar project.
Once the calculation has been obtained, it is possible to verify the correspondence between the calculation and the entities calculated directly on the 3D model even from a visual point of view.
This is possible because a 5D BIM software is also an IFC Viewer or a tool to open and view IFC files of 3D models created with any BIM authoring software. Essentially, it allows you to upload multiple IFC files in a single view, to simultaneously view all the design aspects in an integrated way (architectural, structural, plant design, etc.).
In addition to viewing the geometric model, it is also possible to consult all the properties and information assigned to each element of the 3D model (materials, volumes, surfaces, weights, etc.), also by setting filters and custom selection groups.
What are the main benefits of using BIM for cost estimating?
The transition from CAD design to 3D BIM modeling has several advantages for construction professionals not just in terms of precision and efficiency but also for cost estimation.
Here’s a list of the main benefits of using BIM based models when producing cost estimates:
- fast, automatic quantity detection directly from the 3D model;
- automatic updating of the cost estimate during each change made to the project;
- quantity calculations are updated more quickly, saving time and also avoiding errors;
- better cost control for construction companies and clients;
- accurate estimates and realistic budget forecasts;
- sharing of the IFC model (an open and non-proprietary format) together with all relevant information (including cost information) to facilitate collaboration with other project team members.