The changing pace of design and technology within the construction industry has inevitably led to a certain amount of confusion along the way. As new methods, processes and software arrive, some will manifest as developments of older forms while others might develop in parallel — seeming superficially similar but in fact intended to be used for distinctly different applications. Others are complementary but with definite unique qualities that can be overlooked by the layperson.
The confusion regarding CAD, BIM and VDC is a case in point. The most frequently heard question regarding BIM from those unfamiliar with the process is: "isn't that just 3D CAD?" Similarly, VDC is often mistaken for BIM and vice versa. To some degree, it all depends on which technology or process a user has first become familiar with. To those that are up to speed with all three, however, the distinctions are quite clear.
CAD, or Computer Assisted Design, is the oldest methodology of the three. This is a design and documentation tool that uses computer technology to arrive at the most accurate, comprehensive and information-rich model within its parameters. It is typically used for designing and engineering complex projects, from mobile phones to aeroplanes to buildings, which include multiple precision parts and components.
CAD utilises both 2D drawings and 3D models. 3D CAD has been standard in manufacturing since the 1990s and has benefited the industry enormously in terms of allowing more complex design work to be executed quickly and more efficiently. Its widespread adoption was largely driven by the need for businesses to remain competitive, as 3D CAD enabled products to be delivered to market a lot faster than before, and so any company not using 3D CAD would inevitably lag behind. 3D CAD has been increasingly used for the design of buildings.
The Arrival of BIM
While CAD is a technological tool, BIM (Building Information Modelling) should be understood as a process of collaboration that is facilitated by the latest digital technology. By providing a holistic approach to construction that unifies design, building and documentation across a project's lifespan, BIM has caused considerable positive disruption to the construction industry in recent years. The key difference between BIM and 3D CAD is that a BIM file is much more information-rich, and includes details of performance characteristics, specifications, and other non-physical data embedded in a shared 3D digital model of the project.
BIM is a technologically enabled process of collaborative design and production that allows architects, engineers, clients, and contractors to collaboratively work together in a single model — both simultaneously and in sequence. Using a shared computer-generated model and database, decisions can be made and problems defined and solved prior to the project "breaking ground". Clash detection and coordination across trades can be resolved in coordination meetings prior to construction — avoiding delays and issues in the field. This saves time and money as well as reducing environmental impact. BIM also allows for more complex and ambitious 3D design to be realised successfully and safely.
A BIM representation will involve a digital model of the project that includes all functional systems and aesthetics, such as electrical wiring, air conditioning, doors, windows etc., as well as geometric features. It is a shared multi-disciplinary resource allowing all those working on a project to share information and working processes in order to achieve maximum efficiency and effectiveness. BIM encourages and facilitates communication and collaboration by using the latest digital technology. The design-to-construction workflow is significantly overhauled as a result, and the BIM model will remain in place once construction is completed, as a vital one-stop reference tool that can be continually updated as required.
However, it is important to emphasise once again that BIM is a process rather than an application or tool. For it to be fully functional, all parties need to provide as much information as possible, including the manufacturers of parts and materials. While 3D CAD allows features and components to be broken down into their constituent parts and analysed (with different models able to be combined for clash detection), BIM is much more information-rich. Component products can be identified according to a master specification system including qualities such as minimum standards, conductivity and so on. Acoustic, aesthetic, structural and/or thermal performance requirements can also be included. A BIM representation can be considered a smart object or parametric model that changes in all views if any one input is updated.
VDC, or Virtual Design and Construction, is the most difficult of the three terms to define — there is no single agreed upon understanding of this phrase. The use of the word 'virtual' is perhaps misleading here, as this implies that VDC is a form of digital software. But, although information technology will almost certainly be used, VDC like BIM is a process and a way of working that involves the management of integrated multidisciplinary performance models. It is a way of coming up with an ideal strategy for a given project that incorporates the right people and the right technology. VDC emphasises collaboration and integrated working, and BIM is frequently a valuable part of VDC. BIM and VDC should not be considered analogous, however. Virtual design and construction need not necessarily involve building information modelling, and building information modelling can be undertaken without it being considered part of virtual design and construction. BIM is a much more specific process than VDC, but both are essentially methods of planning and managing a project collaboratively.
3D CAD is now seen as the minimum requirement in most design sectors. But where CAD is generally used for industrial design of objects and vehicles, BIM is fast becoming the industry standard for design within commercial construction. For instance, the building of schools, office blocks and transport hubs like airports or railway stations. Going forward, it also seems clear that VDC will become the standard methodology for approaching complex major projects, incorporating 3D CAD or BIM as required. These are complementary technologies and processes for the most effective sharing of information on any project, allowing for clearer understanding, stronger communication and a collaborative approach that will benefit the construction, design and engineering sectors across the board.