What Are The Differences Between BIM and CAD?
Posted on 11th February 2021
Categorised as bim, cad

CAD (Computer-aided design) has been used in the design industry for 30 years or more. It enables the fast production of drawings and the ability to revise designs or reproduce alternative proposals very quickly.

CAD has proved to be an essential tool in communicating designs to stakeholders, but the advent of new technology has raised client expectations and now drawings alone are often not sufficient.

Building Information Modelling (BIM) is one of these new technologies. Its primary focus is the development of buildings within collaborative working environments and has shown to be a game-changer in the industry. Measures such as the UK government BIM 2016 mandate and cloud computing have driven the BIM process forward.

There is a correlation between BIM and CAD but they are quite different. BIM is a process used for the entire life cycle of a building. 3D modelling is just a part of that and to add to the confusion CAD can be part of the BIM process too.

Here we look at the differences between CAD and BIM and how each is applied to the construction industry.


CAD diagram

CAD has been around for a long time and used in the Architecture, Engineering & Construction (AEC) sector for about 30 years. It was designed and is used as a direct replacement for the drawing board. It enables faster production of drawings (Plans, Elevations, Sections and Details) and amongst its core strengths, certainly over hand draughting, is the ability to revise designs or produce alternative proposals very quickly.

CAD has proved invaluable on large projects where the requirement to bring design drawings together from different disciplines for coordination purposes is easily achieved and many on-site issues averted.

CAD has evolved over the years and now incorporates 3D functionality allowing users to develop complex projects and enabling a better understanding of design constraints and allow clients to more fully visualise the design.

Nowadays designs can go from preliminary concept design to on-site construction far more quickly than in the past.

CAD Advantages and Disadvantages

CAD has been at the forefront of AEC design technology over recent decades but it has had its limitations, in many ways its success and the market dominance by a few companies has held the CAD process back. Some of the advantages and disadvantages of CAD breakdown as follows.

CAD Advantages

  • Compared to the drawing board that it replaced CAD software offers a range of tools to aid the production of drawings including high precision linework, easy replication of tasks and drawing objects, import of premade CAD objects directly from manufacturers and direct import of site survey data.
  • Drawing revision is a far simpler task. Design changes, corrections and amendments are more easily incorporated into new versions of a drawing whilst (if required) leaving the previous version on file.
  • Supporting access to multiple teams on a project. Teams can access and use a drawing on a project either for coordination purposes in their own files. Or contribute to a single federated model combining complex drawings from multiple disciplines.
  • Easy recreation of drawing files allows for a clear audit trail of the file with many CAD packages linking to external document management systems with version control.
  • Product design information can be stored within the drawing. For example, serial numbers and technical information can be attributed to objects within a drawing for access later.

CAD Disadvantages

  • Drawing plans, elevations and sections in most CAD systems creates elements that are not dynamically linked to each other, therefore when a change is made to one it has to be manually updated on the other. This disconnect can often lead to unseen errors being discovered on site.
  • Like many other software packages CAD has a vast array of functions. Without ongoing training, users will learn enough to get the basic drawing done without utilising the advantages of a well-structured CAD file and CAD process. Adherence to design and CAD standards enables greater efficiencies across a complex project.
  • CAD files are not great at handling very large data sets such as GIS data, in addition, coordinate systems are often ignored or misunderstood in the CAD environment.
  • Although not specifically the fault of CAD, ‘As built’ drawings are too easily fudged in CAD and that precision data is soon lost.


BIM Model of underground pipes

Building Information Modelling is a process or design methodology; it is not just another CAD tool. BIM was given a boost in the UK when the government mandated that from April 2016 every construction project funded by central government was to be delivered with ‘fully collaborative 3D BIM. Since the mandate came into force, there has been a rise in levels of BIM adoption.

In particular, the 3D modelling aspect of BIM makes good use of the cloud allowing all project members to collaborate with real-time ability to update the model, this allows for quick changes as required. When used at its best BIM aids the entire project team to visualise and analyse the project, spotting construction issues before reaching site.

Sustainable BIM methodology enables the design of every aspect of the building not just the building envelope itself. Mechanical, Electrical & Plumbing (MEP) features can be incorporated into the model and analysed for interference. Sun, shadow, heating and right of light can all be studied.

Used well, a 3D BIM model holds information about the building within the model for the lifecycle of the building.

BIM Advantages and Disadvantages

BIM offers a more complete solution than CAD and addresses many of its issues but there are still some drawbacks.

3D Revit Model of the exterior ofHouse of Fraser, Cardiff

BIM Advantages

  • BIM is usually a more detailed or complete view of a building in digital form. It includes the building structure but in addition the MEP components. The clear advantage being that any clashes are discovered early as well as the impact of the building on the local environment, all before reaching site. Designers have a clearer understanding of the 3D space and can make more efficient use of it.
  • With a cloud-based model many designers can work simultaneously on the building, eliminating the too frequent problem in CAD of working on outdated files. Documentation is stored in a single database and more easily accessible. An up to date dynamic model leads to more efficient project progress.
  • BIM Models are more easily understood by clients and can be very quickly developed into high-end visualisations.
    Technical information relating to every part of the building can be stored within the model accessible to the user at any time in the building lifecycle; Design, Construction, Maintenance and demolition.

BIM Disadvantages

  • The uptake of BIM is still patchy across the AEC sectors partly because it is new and a lack of widespread expertise.
  • It is regarded as overkill for many smaller projects where the investment would be too high and CAD drawings will be sufficient.
  • Due to the shortage of BIM specialists in the sector more needs to be invested in training and in new software and technology.

CAD and BIM are different but exist in the same sphere. CAD is primarily used for the development of plans and some 3D models. BIM a methodology used in the creation of integrated models for use throughout the life of a building.

If you would like to learn more on this and how Benchmarq can assist you with you CAD and BIM requirements, please get in touch at info@bmarq.co.uk.

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