Since the development of CAD over half a century ago, design processes within the construction industry have changed dramatically, seeing traditional pencil and paper plans tossed out in favour of 2D digital drawings. As computing technology advanced so did CAD, expanding its capabilities to 3D and more recently CAD has fuelled the development of Building Information Modelling (BIM), a process that ties visual design with intrinsic product data together.
Although BIM has been making waves in the construction industry, it is often used as a buzzword without full understanding of how the process actually differs from the traditional CAD process – With some people even using the two terms interchangeably.
What is BIM?
The National Building Information Model Standard Project Committee defines BIM as ‘a digital representation of physical and functional characteristics of a facility.’
What is CAD?
CAD technology Is used to create precise designs and technical illustrations for products. Illustrations can be produced in either 2D or 3D format.
Given the above definitions, it is not difficult to see why some people struggle to differentiate the design tools. After all, BIM is essentially an enhanced form of CAD modelling. Whilst traditional CAD and BIM may not be mutually exclusive, it is important not to confuse the terms as the outputs produced and project efficiencies achieved differ significantly between the two.
Differentiating CAD and BIM
- Design Principle
While BIM tools such as Revit are essentially CAD programs, the term "CAD" is typically used to refer to drafting programs. In terms of building design, CAD involves using drafting software to create lines and arcs that represent a buildings design. The drawings are conceptual designs containing no physical product data to assess project feasibility. As a result, construction conflicts can be harder to identify during the initial design phase, increasing the likelihood of problems arising during installation.
Alternatively, A BIM model is much more than a visual design model and represents the physical and intrinsic properties of a building as an object-oriented model connected to a database. BIM allows you to use up to date digitalised data that represents the exact properties of a manufacturer’s products within a 7D environment in one centralised model for efficient project development and management.
By utilising manufacturer specific BIM models, approval of final as built design can be gained based on exact manufacturer product properties including weight, electrical ratings, etc. to ensure the project runs smoothly with a lessened risk of conflicts arising later in the project. The earlier that conflicts are identified and resolved, the less adverse the impact will be on project timeline and cost.
To summarise, Traditional CAD is limited to visualizing the design features of a project and how they fit together. BIM provides an enhanced view and helps stakeholders to plan the building life cycle, with processes such as cost management, construction management, project management and facility operation through one central BIM model.
In a traditional CAD workflow communication between stakeholders can be quite fragmented. Every construction project will involve multiple disciplines from electrical engineers and structural engineers to drainage experts, all of whom will produce CAD drawings for their individual discipline. This results in a plethora of project documents, all of which must be properly coordinated and updated to reflect project changes. When data is shared in batches and in an untimely fashion, it tends to go back and forth between stakeholders until all plans are up to date before approval can be given. This can be an extremely tedious process and is a major contributor to increased project costs.
As BIM is a shared knowledge resource for information about a facility, information is accumulated and shared transparently between stakeholders to facilitate better collaboration. Plans for each discipline are stored centrally requiring modifications to be made once and in one view which will automatically update in all other views. The impact of any changes can then be assessed in real time to identify conflicts between disciplines and avoid unnecessary rework during later stages of the project.
3. Lifecycle Value
CAD Drawings can be used throughout the lifecycle of a facility for management purposes. For instance, when carrying out additional building work facility managers can use CAD drawings to locate electrical hazards to avoid any costly power outages. However, as traditional CAD drawings do not hold any specific product data their usefulness is limited
When manufacturer specific BIM objects are used to create a BIM model, the model acts as a digital twin for the real-life structure. This means that the model can be continually updated to reflect the evolution of the building and data built into the digital product model can then be used to improve the efficiency of maintenance procedures. For instance, facility managers can use the live model to identify the best access route to a defective electrical component and retrieve the exact part number to order a replacement in a timely manner.
Whilst the basic principle of both CAD and BIM is to produce a visual representation of a building’s design, the differences lie in the advanced functionality and level of detail that can be achieved through BIM. However, the true value of BIM can only be realised where manufacturer specific models are used, and real-life product values are being reflected in the BIM environment.
BIM doesn’t replace the role of CAD In engineering entirely but does provide a more efficient method of creating as-built project models that are multidimensional and can benefit the client at each stage of the process i.e. design, costing, maintenance, project expansion.