Nzangi Muimi

5D BIM Modelling Principles from a QS Perspective

What is BIM?

Construction is a very capital-intensive industry. The key measures of success in the industry are the proper management of costs, time and quality. Quantity surveyors are key professionals in the construction industry as they are in charge of managing costs and time, which are important aspects of a project’s success.

Advances in information technology and computing have seen the construction industry transition from traditional paper-based construction documentation, to computer-aided design and drafting (CADD) and computer-aided estimating (CAE).

These advances have resulted in the automation of tasks, with architects, engineers and other designers saving time by designing faster. Consequently, a faster cost-feedback is required from the quantity surveyor to help in the development of a cost-effective solution for their clients.

Further, a more collaborative way of working developed from the early 1970s is even proving more beneficial to other Architecture, Construction and Engineering (AEC) industries the world over. This is called building information modelling (BIM).

By definition, BIM is a collaborative approach to project delivery that integrates project participants in a single shared project database, where key information required for making decisions about the facility being built is found and continually updated.

This methodology is enabled by technology through BIM-supporting software. It is based on the work processes of the people involved in the project, with a recognition of the industry procedures and government regulations that govern the construction industry.

In a more holistic sense, we can look at BIM as not just building information modelling, but it extends to information management and optimization. The management part shifts the focus back to the people and their processes of generating, collecting, storing, retrieving, disseminating, and sharing data/information about the proposed facility.

In addition, information optimization helps us recognise the need for making the best and most effective use of this project’s information. The building information model is not just packed with information, but the right information to help make project-based decisions.

Therefore, the focus is on the project participants being aware of the decision-supporting information requirements of others and producing and sharing the right information, at the right time, in the right file formats, and with the right details to help them make decisions faster and execute the project efficiently. The underpinning technology and associated software are just enablers due to their automation capabilities.

Level of BIM Adoption in Kenya

Kenya, with an ambitious goal of becoming a middle-level economy by 2030, cannot close her eyes to the role of digitization in helping achieve this goal. With the construction industry contributing 6.7% of the GDP (Economic Survey, 2022), digitization and automation in this sector are key.

According to Mosse, H.N., Njuguna, M. and Kabubo, C. (2020), architects in Kenya are the leading adopter of BIM with an adoption rate of 70.3%. Quantity surveyors are lagging with the lowest adoption rate of 38.7%.

Architects are followed closely by MEP engineers with 66.7% and 64.3%, Construction Project Managers with 59.5% and Civil Engineers with 46.9%.

Are the quantity surveyors missing out? Amongst other challenges, the BIM models supplied to the QS for carrying out cost estimations lack the consistent quality that would allow quantity surveyors to automatically extract quantitative data from these models for cost estimation. The incomplete models force the QS to revert to the 2D-based estimating and quantity take-off to guarantee the accuracy of their outputs.

Further, even with the architects and designers leading in BIM adoption, the maturity level has not reached a point of full integration of construction information in a cloud-based environment by use of a common shared model.

The Kenyan Architecture, Engineering and Construction (AEC) is still in partial collaboration. Users have shifted from a paper-based approach to a mix of 2D and 3D pieces of information, shared and exchanged online using email and other instant multimedia messaging platforms.

It is common to find several 3D BIM models in the same project (architectural, structural and MEP). There is still a risk of element duplication in these models with fewer data to aid the QS in automating his processes.

The low BIM adoption rate amongst quantity surveyors can be explained by these challenges.

BIM and the Role of Quantity Surveyors

The traditional project delivery process involves the architect translating the client’s brief to drawings and sharing that with the structural engineer for structural input, and the QS for cost feedback. As the design progresses, it becomes a series of design – cost feedback – redesign – cost feedback processes that are lengthy and time-consuming.

The quantity surveyor is costing a completed design without helping the architect design to cost. To create more value, a shift to design to cost is necessary. The role of the QS early in the project moves to provide cost information that will be used to influence design.

However, this cost feedback is not timely because the traditional QS will take more time taking off quantities, manually counting items and preparing cost estimates. Where the architect is adopting 3D BIM, modelling faster, cost feedback from the QS is slow. We can see that although the design and cost estimation is not entirely disconnected, they are not fully integrated.

With the implementation of BIM, quantity take-off and production of bills of quantities will be automated. Precious time wasted by the QS manually counting items will be freed and can be focused on offering more valuable cost advice to the design and client teams, and exploiting his commercial management knowledge for the success of the project.

Further, 3D BIM (three-dimensional architectural/structural/MEP modelling) makes it possible the development of information-rich models during the early phases of the project. Since this is like a simulation phase before the actual facility gets built, it is more cost-effective to develop as many design iterations as possible to come up with the most cost-effective one.

The QS focus shift more to this phase, to collect cost information, continuously feed it to the BIM model and verify and validate model data as it develops. This tied with a simulation of the construction schedule, helps predict costs and advise the project team accordingly.

This brings back cost as a parameter for choosing a viable design. Design and cost estimation become concurrent, with almost instant feedback as the model evolves.

This is possible because BIM models are an aggregation of a library of intelligent objects linked to a database rich in non-graphical metadata. It contains geometric data of the building elements, a description of the properties of the building components and details of the interrelationships between these properties and the building components.

When an update is made on the BIM objects, it automatically updates the relevant views (3D, plan, sectional, elevational and detail) and non-graphical and cost-related data found in the elements schedule.

Therefore, quantity changes when a design is revised will be automatically updated and the QS will not be required to remeasure. Revolutionary, right?

However, it should be noted that with this BIM approach, the quality of the estimates developed by the QS will be highly dependent on the quality of the information models produced by the designers. If important quantities cannot be extracted from the model, it is only good for the QS as a visualisation tool and manual take-off processes from 2D drawings will be better.

Also, even with a very detailed BIM model, not all building quantities can be extracted from the model. Items like concrete volumes can be based on volumes of modelled beams, columns, and slabs; door architraves and formwork to columns may not be modelled but can be derived from the model items. Other items such as planking and strutting, general site conditions, means and methods of construction cannot be modelled.

These will require the QS to capture them in his cost and pricing databases that exist outside the BIM model and feedback on the information to the BIM database for a more holistic cost estimate.

Therefore, manual quantity take-off processes cannot be overlooked. They will serve to verify and validate quantities extracted from the model and to incorporate non-model quantities into the QS estimates.

The QS professional training, knowledge and judgement play a key role in the BIM environment. It is required to interrogate the model for completeness required for quantity extraction, determine what has been captured by the model and what has not been captured and integrate rules of measurement to come up with a proper bill of quantities.

As discussed above, BIM will make the quantity surveyors more valuable in the industry as quantity extraction automation will free their time to focus on giving more valuable cost advice to their clients. This will lead to quicker and more frequent cost feedback to the designer in the early phases of the project, making cost control very effective.

However, the adoption of this collaborative technology is highly dependent on the quality of the BIM models produced by the architects and designers. Do they meet the requirements that can support the QS in producing accurate cost estimates? Otherwise, if they are just nice graphical models with fewer cost data and uncoordinated model items, they are not useful to the QS. That will be a huge barrier for the QS to implement 5D BIM in their workplaces.

Model Content Optimization: Improving the Usability and Reliability of the BIM Model

We have discussed the role of the QS as a model consumer and how important it is for the model producers to be aware of the information requirements of the model consumers and package the information in a way that helps them achieve their objectives.

To support the QS to implement/adopt BIM, the architects, engineers and designers should observe certain modelling principles that will help them create BIM models that are accurate and rich in usable information that the QS can rely on in producing accurate cost estimates.

Since computers operate on the GIGO (garbage-in, garbage-out) rule, the quality of data incorporated in the BIM models determines the quality of the information that will be extracted from these models. This quality can be assured through the adoption of model optimization practices with the future needs of other project members (especially the quantity surveyor, contractor and facility manager) in mind.

The usability and reliability of the BIM models can be improved by observing the following modelling principles and ways of working:

1. Have a BIM Execution Plan (BEP)

As the lead consultant, if you intend to implement BIM in your projects, ensure the whole project team agrees early on how they plan on collaborating, what information will be produced and the methods of sharing that information.

The development of this BIM execution plan should be done at the start of the project when every project member has been appointed to the team to ensure their participation.

The aim is to help the project members understand their roles and responsibilities for model creation, maintenance and collaboration at different stages of the project. It will help to set clear the data requirements of each member, the information exchange protocols and the technology infrastructure and software that will be adopted during the project.

When everything is set out and agreed upon, it is easier to measure the progress and success of the project.

2. Develop and Agree on a Model Content Plan (MCP)

A model content plan is usually included in the BIM execution plan. It sets out what should be modelled, the level of detail and at what stage of the development these elements should exist in the model.

When it is developed and agreed on, it becomes easy to measure and control the quality of the model. Quantity surveying information requirements will be captured in this document. Therefore, making it easy for the designers to create, place and export their models in a way that enables this information to be used for quantification purposes.

A model content plan is important because it will help the model creators to model accurately and accurately manage important data, and subsequently pass it to model consumers in the right details and formats to aid them in performing their functions that depend on that data as their inputs.

3. Use Modelling Tools Correctly

BIM model authoring software usually has design and modelling tools for modelling the various building elements in a 3D environment. Quantity schedules extracted from these models capture information and group it based on these elements.

If a wrong tool is used to model an element, the resultant element quantities will be reflected in a different category, resulting in estimation errors.

Therefore, make sure to use the right design tools for the right building elements when modelling. For example, don’t use a slab tool to model walls. Quantity schedules will capture the slab concrete quantities instead of capturing the area quantity for the walling.

4. Avoid Lazy Modelling

The project should be modelled the way it will physically appear in the real world. The model creator should strive to capture an actual representation of the physical facility, including its finishing accurately. This will improve the accuracy of cost estimates derived from the model.

Also, 2D drawing using linework should be avoided as much as possible, especially where the modelled items are required to be costed. This is so because 2D linework will only represent the item well in a 2D plane, but will lack 3D geometric data and other important non-graphical data used in cost estimating.

Where 3D forms, morphs and extrusions are used, they should be properly tagged with a proper description, appropriate quantity and cost data, and manufacturer details. Generic forms without the said data will not be reliable for cost estimating.

5. Share your Models in Native or Open BIM Formats

Due to the diversity in the project teams, different consultants use different BIM software to create models, perform simulations and extract quantities for cost estimating. These software applications are not developed by the same vendor and have differences in how they describe, calculate and measure quantities.

For example, an architect may use Revit to create a model; while the QS use Cost X to perform quantity take-off and bills of quantities preparation.

Due to the interoperability challenges, it is always advisable to share your models in the native proprietary file formats so that important data is not lost in the process of conversions. The project QS can open the file in their native formats and interrogate the quality of the model before performing quantity take-off.

Where intellectual property issues are a concern, you can opt to share the model in open BIM formats such as the IFC (Industry Foundation Classes) formats. This internationally recognised standard does not allow the user to edit the original model produced by the designers.

6. Encourage Product Manufacturers to Supply a Library of BIM Objects

Usually, the standard library of objects included in a BIM authority software installation is not exhaustive and may not cover all the items that you want to include in your models. Most architects usually develop their in-house libraries to supplement these standard ones.

However, where data is being exchanged with other participants, the accuracy and details of these will be paramount in helping others understand what you have modelled.

To save time and ensure standardization, model developers should request product manufacturers to supply them with a library of BIM objects for the range of products that they intend to have incorporated into the project.

The libraries from the manufacturers will be more detailed and accurately capture all technical details and specifications of the product. Incorporating this wealth of data in the early phases of the project will help the QS in producing more detailed and accurate cost estimates in the earlier stages of the project.

Consequently, the value of their cost feedback to the design and client teams will improve and lead to better cost control.


We have seen the revolutionary effect of implementing BIM in the QS practice. Automation of quantity take-off and reduction of manual counting of items frees the quantity surveyor’s valuable time, allowing them to focus on adding more value to the project through their cost management, value engineering and commercial knowledge.

However, the quality of BIM models generated by the designers slows down the adoption of BIM by the QS if they don’t contain usable data to aid in performing the QS functions.

To improve the usability and reliability of these models, a BIM execution plan and a model content plan should be developed at the onset of the project to guide project members on the decision-making information needs of others and their role in satisfying those needs.

Also, using the design and modelling tools accurately, proper modelling and tagging of model items with the right descriptions will help improve the reliability of these models for 5D cost estimating operations.

For quantity surveyors, it is important to ensure that you are involved in every stage of the model development. Develop the right IT skills to help you interrogate models for completeness and use your professional knowledge to validate quantities extracted from these models.

In conclusion, shifting the focus to people and their ways of working will help solve most of the challenges that slow down the rate of BIM adoption amongst quantity surveyors. Technology should be seen as an enabler, and all project participants work in collaboration to harness the advantages of the automation that comes with it.

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