Generic or specific…? That is the question.

This week has seen a lot of Twitter debate regarding whether BIM content should be generic or specific. For me this is very clear-cut but the reasons for my view are wider and relate to a drive to improve value in the construction industry.


To achieve this we have to rethink everything from the ground up. Many of the arguments to use generic content are based on existing procurement methods or decisions made at a profession level rather than what is right for the project. By now you may have picked up that I am a supporter of specific manufacturer content being specified as soon as possible.


This position is generated from a pragmatic position and one that eliminates waste. If we review other industries it is unlikely that Ford or Boeing use generic equipment when designing their systems.


The argument for generic content is based on the reluctance to remove a component later in the design stage when the specification changes, which is driven by a design and build procurement route. I would agree that we should not carry out needless work but the only reason for this is one of the selected procurement approaches.


Design and build was developed as a procurement method to move risk away from the client and place a greater percentage with the constructor. I believe much of this risk can now be managed through the structured BIG BIM approach.


If we define and validate the design with accurate data in the first place and then design the building and rigorously prototype proposals the risk will be under a higher level of control. The designer should be allowed to make the right design decision based on a wide range of value metrics. Cost is only one metric but size, weight and performance along with many others may also be relevant. The constructor will often make a decision in cost alone, which may impact on other metrics.


I recently attended a design team meeting and all of these issues were apparent and the shortcomings with generic content became apparent.


We can look at an Air Handling Unit as one simple example to demonstrate the problem.


The Mechanical and Electrical engineer is generally reluctant to commit to a specific AHU manufacturer because he knows the subcontractor is going to go to the market to get the lowest price.


The M&E consultant uses generic design parameters and sizes up to stage E. The architect and structural engineer use this information to design and coordinate the AHU into the design.


The subcontractor now procures the AHU to get the cheapest price. The selection of the AHU is likely to be based on other value issues such as energy use, life cycle, weight and size but these are not considered when deciding on which supplier. The selected AHU was the lowest price by £1,000.


By stage F the team now deletes the generic component and inserts the exact AHU. This starts a cycle of change and redesign. Firstly the selected plant is bigger than the generic component. The architect has to redesign the roof plant room. It is also noisier so the external fabric requires additional acoustic treatment. The selected AHU is also heavier than the original. All of the steelwork has to be upgraded and changed.


The selected AHU also has a higher running cost year-in-year than had been anticipated. The extract air is in a different location, which means all of the ductwork has to be redesigned.


Standing back from the generic content and the late specification, which saved £1,000, accrued cost £5,000 in re-design, £5,000 in delays because the steel had to be changed and £30,000 in the building life cycle due to increased running costs.


This is one example of generic constant. If this is across all components just imaging the wasted time and cost to the project. Whilst it may have save the subcontractor it has cost everyone else. If we are trying to eradicate waste and rework, this workflow and procurement is clearly wrong.


Why can’t the designer select the right AHU based on the decisions made at the ‘define and validate’ stage? At this point value will have been clearly defined and allowing objective decisions to be made.


The accurate AHU can then be located and coordinated. The designer can use his expertise and should stand by the reasons for his specification. Any specification decision is not only based on cost and BIM will provide a method of demonstrating these decisions objectively and with accurate data.


I see little place in the design and procurement process for generic content if we are looking to deliver the leanest design and construction process.


If organisations continue to focus on their own positions rather than the bigger project picture, they will continue to promote the use of generic content.


As someone who is passionate about maximising value in delivery and operation I think we should make informed decisions using the best innovative products.