An Introduction to Set-Based Design

Set-based Design (SBD) is a design methodology that has many applications in the architecture, engineering, and construction (AEC) industry. It was discovered when researchers studied the engineering and design process at Toyota [1]. Known as the “second Toyota paradox”, the researchers were surprised to find that Toyota considered a broader range of possible decisions, produced more physical models, delayed key decisions longer, and yet they had the fastest and most efficient vehicle development cycle in the industry.

In order to better understand SBD, we need to first consider the traditional design process. Most design professionals (and most people in general) who have not been exposed to SBD follow a linear process. Known as point-based design, this linear process starts with an initial concept and then progresses towards greater and greater detail of the concept. At first, this process seems very efficient since you are only working on one concept from start to finish. In an ideal world, this would be the perfect design process.

Unfortunately, the world isn’t linear and is often more complex. With point-based design, if at any point in the design process a new constraint comes up or new customer requirement is added; you have to start all over again. Sometimes you move all the way back to square 1.

Rather than selecting one promising option and working on it further, set-based design looks at a wide range of possible options. The sets of possible solutions are gradually narrowed down until it converges on a final solution. Along the design process, some options are eliminated due to hard constraints, infeasibility, or lack of fitness. Ideation can also be used to generate more options. At the Last Responsible Moment (LRM), the decision needs to be made and one of the option is selected.

By starting with a wide set and gradually eliminating weaker solutions, more options can be evaluated and better solutions can be found. In the event of an unexpected or a new constraint, there is a less likelihood of having to start from scratch since one or more of the options will already meet the new requirements. If necessary, you move back one or two paces. This is much better than starting again from the beginning.

For those that want to apply Set-based design, here are few principles of the process [1]:

  1. Define feasible regions.
  2. Explore trade-offs by designing multiple alternatives.
  3. Communicate sets of possibilities.
  4. Look for intersections of feasible sets.
  5. Impose minimum constraint.
  6. Narrow sets gradually while increasing detail.
  7. Stay within sets once committed.
  8. Make decision / selection at the Last Responsible Moment

Choosing By Advantages

The application of SBD ultimately relies on an effective method for decision-making. The most robust method that we know of is called Choosing By Advantages (CBA). CBA and set-based design has been used on a variety of Lean Construction projects to make the design process more efficient.

Choosing By Advantages with alternatives from Set-Based Design

Many advanced Lean Construction teams use SBD and CBA with the Last Planner System in design. The Last Planner system allows the team to map out the series of important decisions and milestones. SBD allows the team to explore the viable options while considering the needs and constraints of the end users. CBA helps complete the process by providing a reliable, transparent, and robust methodology for making and communicating decisions. Together, SBD, CBA, the Last Planner System help support Target Value Delivery. These Lean practices help project teams enhance the efficiency of the design phase and deliver greater value for the money to their clients.



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