Achieving an understanding that BIM and CAD are as different as chalk and cheese is the first step to delivering better buildings, efficiently and at a lower cost.

We need to understand what CAD is before exploring BIM. Many might remember drawing boards, indeed some feel there is something intrinsically satisfying in the art of draughting.  

CAD (Computer Aided Design) is hardware (computer) plus software (for example AutoCAD) used to create designs of anything from buildings, products, to parts etc. A more eloquent definition from the world’s leading software developer Autodesk, (maker of AutoCAD, Revit, 3DS Max, etc.)

CAD is “the use of computer technology for design and design documentation. CAD software replaces manual drafting with an automated process”.

The power of computing and the breadth of the functionality and capability the software delivers means designs can be produced in a fraction of the time of manual draughting. Amendments can be made very quickly and the designs distributed to anyone in seconds leveraging the power of the internet.

Notwithstanding the improvements in productivity, meaning more time for quality and related tasks, the overall approach, methodologies and concepts are not dissimilar to manual draughting. You might describe the transition as replacing the horse and cart with a car. Same journey, different level of comfort, speed and amenity.

Many design organisations use CAD in 2D and/or 3D guise. Differing levels of adoption and investment, resources and expertise will produce varying degrees of success, return on investment, breadth and depth of capability.  However, step changes in overall quality, joined up integrated design and construction, performance of the building, are unlikely to be attainable. Turbo charged car perhaps, but it’s still a car?

On first look, BIM software looks similar to CAD software, more advanced features but hardly chalk n’ cheese? Extending the car analogy, maybe it’s a hybrid?

You know BIM is very different to CAD when you try and digest published definitions:

Building Information Modelling (BIM) is an intelligent 3D model-based process that equips architecture, engineering and construction professionals with the insight and tools to more efficiently plan, design, construct and manage buildings and infrastructure.


Building Information Modelling (BIM) is a digital representation of physical and functional characteristics of a facility. A BIM is a shared knowledge resource for information about a facility forming a reliable basis for decisions during its lifecycle; defined as existing from earliest conception to demolition.

The US National BIM Standard Project Committee.

BIM is a process and methodology which enables and supports all participant’s work collaboratively using the same computer 3D model and database. You could describe CAD as about lines, arcs and circles to define a design. BIM is a database of data and information that allows a digital representation of the building and its systems.

As a consequence assessments, analyses and testing can occur, possibly with the benefit of further add on software modules to understand how the building might perform over time. If nothing else, environmental considerations mean an assessment of a proposed buildings carbon footprint across its lifecycle.  Try such assessments with mere CAD files!

BIM is not dressed up CAD. It may, for new users be a steep learning curve, without expert guidance, training and support. Once the concept and processes are embraced, it offers a real step change in how buildings are conceived, designed, constructed and managed for a brave new world where resources become scarcer and expensive.

Tony Reece MSc CEng MICE is director of Cadassist Limited (part of Symetri Group) – delivering CAD, BIM and Data management solutions to Architecture, Engineering and Construction sectors for over 25 years. Cadassist are the No1 Autodesk Authorised Training Centre in the UK.

Contact the author: / 0845 872 5555 (Manchester).


BIM Scotland 2019

Strathclyde University, Technology Innovation Centre. See us at STAND 9.