What is BIM? Building Information Modelling (BIM) uses software to create a model of a building that reacts to change in the way that the real building would. It is designed to make an integrated and collaborative approach to construction possible.

This guide was last updated in April 2012.

Some users use BIM systems as advanced Computer Aided Design (CAD), others as a series of models for distinct elements of a project. For those at the cutting edge, a single integrated model is the goal. Its users hope that BIM can achieve cost savings and ultimately include integrated cost modelling, construction sequencing and facilities management capabilities.

Where CAD depicts construction elements with lines that define a structure's geometry, BIM creates each element of the structure as an ‘intelligent’ object containing a broad array of information (parametric data) in addition to its physical dimensions. Each element in the BIM model ‘knows’ how it relates to other objects and to the design in general.

Within BIM walls are objects which can be stretched, joined and moved, and which ‘know’ that they have certain properties and characteristics. For example, a wall in the BIM model ‘knows’ that it is supposed to extend from foundation to Level 1. If either of those parameters changes, the height of the wall will automatically adjust to match. Similarly, doors and windows ‘know’ their relationship to the walls in which they are placed and behave accordingly.

Designers can use BIM to explore alternative concepts, conduct value engineering and optimise their designs. Contractors can use a BIM model to ’rehearse’ construction, coordinate drawings and prepare shop and fabrication drawings. Owners can use the model to optimise building maintenance, renovations and energy efficiency, as well as to monitor life cycle costs. BIM enables collaboration among designers, constructors and owners in ways the construction industry has never known before.

BIM software

There are two kinds of BIM software: authoring software and coordination software. As the technology matures single software packages may be used that contain both elements.

Common authoring software platforms include: Autodesk Revit Architecture; Bentley Systems; Coordination Software; Autodesk Navisworks, and Bentley Projectwise.

BIM coordination software is potentially revolutionary for construction management and contractors in particular. This software takes the model made by the authoring software and attaches cost, scheduling and other information to it thus creating a tool for achieving improved project delivery.

Levels of BIM maturity

BIM is being used at the moment at a number of different levels of sophistication:

Level 0           Unmanaged CAD, in 2D, with paper (or electronic paper) data exchange.

Level 1           Managed CAD in 2D or 3D format with a collaborative tool providing a common data environment with a standardised approach to data structure and format. Commercial data will be managed by standalone finance and cost management packages with no integration.

Level 2           A managed 3D environment held in separate discipline 'BIM' tools with data attached. Commercial data will be managed by enterprise resource planning software and integrated by proprietary interfaces or bespoke middleware. This level of BIM may utilise 4D construction sequencing and/or 5D cost information. The Government’s BIM Strategy Paper calls for the industry to achieve Level 2 BIM by 2016.

Level 3           A fully integrated and collaborative process enabled by 'web services' and compliant with emerging Industry Foundation Class (IFC) standards. This level of BIM will utilise 4D construction sequencing, 5D cost information and 6D project lifecycle management information.

In the future it is hoped that all members of the professional and construction team will have invested in compatible technology, will have trained their staff, and will have fed design information, costing and programming information and other material into the single, centrally managed BIM model.

It is likely to be some time before BIM systems are so universally used, and to such a high degree of sophistication. Whilst many larger organisations are already making full use of BIM systems, even they have some way to go to achieve the ultimate fully-integrated BIM level.

It will be years before the majority of construction firms make such full use of BIM systems. In the meantime professional team members, contractors, and sub-contractors with design responsibility will find themselves at different stages of BIM preparedness. There will be a small gap between some and a huge gulf between others. Different levels of BIM development will require different approaches; there will be no ‘one size fits all’ during the transition to fully integrated BIM.

Benefits of BIM

In defining the different maturity levels of BIM, the concepts of 4D, 5D and 6D are used to indicate the elements and benefits of increasingly complex BIM models.

There is a wide spectrum of possible uses of BIM on construction projects. At one extreme architects and engineers can use BIM simply to produce better quality design documents without providing the digital model to any other party. Contractors, likewise, can separately create models for estimating, fabricating or simulating construction without sharing the models.

Used in such limited ways, BIM does not come close to realising its full potential. At the other end of the spectrum, BIM can provide a collaborative framework among all project parties, allowing the free-flow of data about what is being designed and how it will be constructed. Collaborative use of BIM takes full advantage of BIM's capabilities.

3D – Model

  • Model walkthroughs. These provide a great visualisation tool enabling designers and contractors to work together to identify and resolve problems with the help of the model before walking on-site.
  • Clash detection. Traditionally design drawings must be coordinated to assure that different building systems do not clash and can actually be constructed in the allowed space. Accordingly, most clashes are identified when the contractor receives the design drawings and everyone is on-site and working. With clashes being detected so late, delay is caused and decisions need to be made very quickly in order to provide a solution. BIM enables potential problems to be identified early in the design phase and resolved before construction begins. Illustrating the advantages of BIM, one project for the General Services Administration in America saw BIM model reviewers find 257 constructability issues and 7,213 conflicts. On the same project, traditional plan reviewers found six constructability issues and one conflict.
  • Project visualisation. Simple schedule simulation can show the owner what the building will look like as construction progresses. This provides a very useful and successful marketing tool for all those involved in a project. Contractors can also use project visualisation to understand how the building will come together.
  • Virtual mock-up models. Often on large projects the owner will request physical mock-up models so they can visualise, better understand and make decisions about the aesthetics and the functionality of part of the project. BIM modelling enables virtual mock-ups to be made and tested for a fraction of the cost.
  • Prefabrication. The level of construction information in a BIM model means that prefabrication can be utilised with greater assurance that prefabricated components will fit once on-site. As a result, more construction work can be performed offsite, cost efficiently, in controlled factory conditions and then efficiently installed. 

4D – Time

  • Construction planning and management. BIM models provide a means of verifying site logistics and yard operations by including tools to visually depict the space utilisation of the job site throughout a project's construction. The model can include temporary components such as cranes, lorries and fencing. Traffic access routes for lorries, cranes, lifts, and other large items can also be incorporated into the model as part of the logistics plan. Tools can further be used to enhance the planning and monitoring of health and safety precautions needed on-site as the project progresses.
  • Schedule visualisation. By watching the schedule visualisation, project members will be able to make sound decisions based upon multiple sources of accurate real-time information. Within the BIM model a chart can be used to show the critical path and visually show the dependency of some sequences on others. As the design is changed, advanced BIM models will be able to automatically identify those changes that will affect the critical path and indicate what there corresponding impact will be on the overall delivery of the project.

5D – Cost

  • Quantity Takeoffs. To determine a project's construction cost and requirements, contractors traditionally perform material ‘take-offs’ manually, a process fraught with the potential for error. With BIM, the model includes information that allows a contractor to accurately and rapidly generate an array of essential estimating information, such as materials quantities and costs, size and area estimates, and productivity projections. As changes are made, estimating information automatically adjusts, allowing greater contractor productivity.
  • ‘Real Time’ cost estimating. In a BIM model cost data can be added to each object enabling the model to automatically calculate a rough estimate of material costs. This provides a valuable tool for designers, enabling them to conduct value engineering. However, it should be noted that overall project pricing would still require the expertise of a cost estimator.

6D – Facilities Management

  • Lifecycle management. Where a model is created by the designer and updated throughout the construction phase, it will have the capacity to become an ‘as built’ model, which also can be turned over to the owner. The model will be able to contain all of the specifications, operation and maintenance (O&M) manuals and warranty information, useful for future maintenance. This eliminates the problems that can currently be experienced if the O&M manual has been misplaced or is kept at a remote location.
  • Data Capture. Sensors can feed back and record data relevant to the operation phase of a building, enabling BIM to be used to model and evaluate energy efficiency, monitor a building's life cycle costs and optimise its cost efficiency. It also enables the owner to evaluate the cost-effectiveness of any proposed upgrades.



BIM has the potential to exponentially improve the process of designing, constructing and operating buildings. However, despite BIM’s vast potential it faces significant obstacles and gives rise to numerous issues which deserve serious consideration.  

  • Different BIM models Ideally, a construction project would utilise a single BIM model used by designers, contractors, subcontractors and fabricators for all purposes. Each party could access the model at will, adding content that all others could immediately utilise. The reality is that for many years there will rarely be a single BIM model. The architect may have its design model, each engineer may have an analysis model for its discipline, the contractor may have a construction simulation model and the fabricator its shop drawing or fabrication model. Interoperability - the sharing of information between these different models - is critical to the collaborative use of BIM, by assuring that each model consistently represents the same building. However, current technologies, and levels of BIM adoption, do not yet allow seamless coordination between different BIM models. The use of multiple models undermines the collaborative use of BIM and prevents project parties from reaping the full benefits of BIM's capabilities.
  • Duplication Some firms may not be able to afford BIM and therefore traditional drawings will still have to be produced to manage the downward supply chain. It is also likely that smaller contractors will not have access to the digital BIM model on-site. Further, most authorities require traditional drawings for planning and building regulation approval. This causes duplication and creates the potential for ambiguity. If, for example, the contractual documents are in 2D but the project is designed in a BIM model – which will take precedence?
  • Ownership In most projects, ownership of the BIM model is likely to be retained by the owner of the building. However, ownership of the data contained within the BIM model itself is a separate issue. Such data is likely to be wide-ranging, and contributions will come from a variety of different participants. For example, there is likely to be design data, cost data, design processes, tables, databases and graphical information. Different laws will govern each of these rights. Enhanced regard to intellectual property provisions is especially important since the BIM model will not only show the results of patented processes and designs, the BIM will actually ‘know’ the building codes, algorithms and applicable engineering principles. It is this information which the system applies to enable the model of the building to be manipulated and updated. Therefore design participants will be required to depart much more intellectual property on a BIM project than they are traditionally used to. The terms of any assignment or licensing of intellectual property rights will therefore be of great concern to all design participants. Increased integration and collaboration also means that there will be complex layers of intellectual property, provided by different design participants, which will be difficult to identify and reverse engineer.
  • Designer's liability exposure In a collaborative BIM model many parties contribute to the design. Crucial details embedded in the design may be provided not by design professionals, but by speciality subcontractors or consultants. In addition, BIM software is designed to react to changes in the model, by modifying elements of the design affected by a change. These circumstances increase the potential liability exposure of design professionals who use BIM collaboratively and risk assuming overall model responsibly.
  • Professional terms of engagement Terms of engagement for all of the project team will need to be considered and drafted to reflect the collaborative nature of BIM and to ensure that responsibilities, duties and services are aligned. Communication and methods of working will need to be outlined to enable those who are not in a direct contractual relationship to work together in order to deliver the project in the integrated and collaborative spirit required by BIM. Provisions on the input of data, limitation of liability and defining the role of any BIM ‘model manager’ will also be crucial.
  • Risk profile. The risk profile for construction projects and project participants will change with use of a BIM model and a collaborative, integrated approach. Measures will need to be taken to mitigate any increased areas of risk. This may require insurance, indemnities, changes to contracts and/or changes to policies and procedures. A balance will need to be struck between the need for fluid collaboration between parties on the one hand and the need to precisely define responsibility to manage the changed risk profiles on the other.
  • Mindset and approach. BIM will completely change the way that designers approach the design process. The level of information contained within a BIM model requires collaboration between different participants at an early stage to establish the initial framework and incorporate the level of detail required. More hours will be spent during the design and less in production.
  • Information technology. BIM places increased reliance upon information technology. With this reliance comes the need for specific precautions such as careful control of access rights and recording of audit trails. Technical support facilities, firewall limitations, bandwidth limits, corruption of data and compatibility issues are amongst the other concerns that need to be considered. The BIM model will be the core of the project and just one error in itcan be very costly. Unlike the traditional approach, with plans that can be checked against one another, BIM plans are generated from the model and reflect the same data. This may allow small miscalculations, which can later lead to big problems that are difficult to spot.
  • Cost BIM models will require significant investment from those across the industry. There will be the direct cost of the software and hardware but also indirect costs such as training and obtaining suitable bandwidth to handle BIM data exchange. Given the level of investment necessary, the industry will take a cost benefit analysis to decide on adoption.
  • Owner – owners are likely to pay for the operation and management of the BIM, for   example, appointing an information or BIM model manager. However, the owner stands to benefit most financially from BIM usage with both construction and operational savings.
  • Designers – designers will have to spend significant amounts on purchasing software, licences, hardware and training staff. There will also be costs incurred from obtaining insurance (with potentially high premiums given the collaborative nature of BIM and increased risk of collective design). However, designers will benefit from advanced design features, such as clash detention and value engineering tools. BIM also has a proven track record as a marketing tool, which provides a clear commercial advantage in any bid process.
  • Contractors – contractors will need to put funding in place to enable BIM software and support to be available on-site through tablet-PCs. However, only with such investment will they benefit fully from the increased level of information in the design, meaning that delay, extensions of time and variations will be less common.
  • Level of detail Contractors are likely to want more detail included within the model so that clashes, delays and extensions of time will be avoided during construction. However, with more detail added during the design phase, design costs will increase and the model will become more difficult to manage and operate. Determining the balance of detail, and how much reliance can be place upon it, will therefore be a crucial issue to be negotiated between all project participants.
  • Contractual implications Historically most contracts are bipartite agreements. BIM has the potential to substantially alter the relationships between parties and blend their roles and responsibility. Risks will need to be allocated rationally; based on the benefits a party will be receiving from BIM, the ability of the party to control the risks, and the ability to absorb risks through insurance or some other means. As party’s journey along the path to fully integrated BIM bilateral contracts, with BIM addendums or protocols, may become unsuitable and collaborative multiparty contracts could potentially become more appropriate. Payment mechanisms may also need to be changed to reflect the fact that BIM projects will become front loaded. Pain / gain mechanisms for collaborating participants may also be favoured. The contract will also have to define the status of the BIM model and deal with post handover matters such as lifecycle management and data capture.
  • Insurance / bond markets Few insurance companies currently offer BIM related products. The rarity of BIM projects to date means that uncertainties remain about its benefits and risks. Insurers are likely to increasingly offer BIM insurance policies but until it is clear what risks are involved premiums are likely to be high. Uncertainly is also likely to impact upon the bond market until BIM becomes more commonplace.
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