In recent weeks, I’ve had several conversations with clients about using smaller batches and takt planning as part of their pull planning sessions on projects. I’m convinced that this thinking should be part of every project running on Last Planner System. Here’s why.
First, we know that smaller batches move faster. This is a direct lesson of Little’s law, which tells us that the throughput time for any stable process is equal to the number of units in flow multiplied by the cycle time. This part is simple math, and it’s the easiest part of the puzzle to understand:
Throughput Time = # of Units in Process X Cycle Time
Unfortunately, in construction, the world is not that simple. In construction, we rarely see a steady process. There are many factors that are constantly working to throw variability into our work flow; things like weather, equipment breakdowns, late deliveries, missing or incorrect design information, late decisions from owners, and a team of trade contractors with differing (and sometimes opposing) motivations and objectives for the work. This is where the Last Planner System comes in.
Last Planner is a process for planning and executing the work of construction with the purpose of creating reliable workflow. The short-cycle planning of the Weekly Work Plan helps the team respond quickly to changing circumstances while coordinating the interests of each team member. Daily Huddles and measuring PPC provide the daily check-ins and fine tuning that’s needed to keep daily production on track and continuously improve the process. Make-Ready Planning identifies problems in advance and provides a process for eliminating them – before the work is interrupted. And Pull Planning is how the team designs the production system for each phase of the project.
When we use batch and takt thinking during pull planning, something special happens. Instead of just considering the interests of each trade in the plan, the batch and takt system provides a framework for the common thinking of the team. This is something that is automatic in a manufacturing process, but very elusive in construction.
I explain it like this. If each party comes to a pull session with their own work in mind (without first considering batch size and takt time), the team struggles to connect a set of activities with different durations and different flow strategies. The plumber wants to move counter-clockwise around the floor while HVAC wants to run east to west and fire sprinkler just wants everyone to stay out of his way so he can knock out the floor out in one week. When we establish smaller batches and a takt time target for the team, it unifies their approach to the work and aligns them to a single flow strategy.
In a conversation last week, we settled on the analogy of the standardized Lego brick. We don’t need every work activity to be exactly the same size. As long as everyone is using Legos from the same set, we know various sizes and shapes will always fit neatly together. Without the framework of small batches and takt time, it could be like trying to build a single structure from Legos, Lincoln logs, and an Erector Set. The pieces are just not designed to fit together.
The picture above shows the outcome of a pull session using a batch size of one-fourth of a floor (still a pretty large batch) and a takt time of one week. The conversation during the session quickly had the team talking about how they could support each other in this approach, and how they would align themselves to move in unison through the project. Even though this was the first pull session for most of them, they aligned around the concept and developed a solid plan. The interesting comment I heard from many of the participants was that, while the plan seemed simple, smooth, and really rather slow, it would allow the work to finish weeks ahead of schedule. This is the magic of combining batches and takt with pull planning and the Last Planner System.
For a bit more insight on how smaller batches move faster in building, see this short video.
And for more ideas on conquering the variability in design and construction work, check out the book, Better Building: Lean Practices for the Project-Drive Organization.