As a foreword to the post, I think there are many ways one can execute Takt time planning (TTP). The fact that there isn’t much research on the topic in construction means that it is definitely an open question. Through some iteration and research, the five step method below is the best practice to Takt time planning so far. The first iteration came from a case study where Takt time planning was used in the exterior phase of construction1.The five steps approach is a logical approach to planning. In fact when I talk with high level folks at construction companies they ‘always do this’. However, when you go on-site and see how people work, their methods are usually quite different than what is prescribed below. Usually their method is founded upon 1) a reliance upon an excellent superintendent to figure out the flow of the job and try to drive everyone to execute according to their plan, 2) inheriting a set of areas from a previous phase of work that may or may not have been created with intent, or 3) some combination of the two.
Step 1 - Data Collection
Developing a Takt time plan requires production data from each trade individually and the team as a whole, well in advance of construction. A Master Schedule may have already been established at this point. Data gathering begins with a production team meeting, consisting of trades involved in the work and the general contractor (GC).
The data to gather in conversation with the trades is specific to them, their work, and the project context. Here are some questions to ask at this step. How do they want to move through this project’s space? What alternatives are available? What are the material and manpower constraints, or work method alternatives? What work needs to be performed before they start work? What is the sequence of work internally (e.g., electricians want to set trapezes, run conduit, and then pull wire)? Can the sequence be split, or can the work be performed in a later phase (e.g., does the electrician have to pull wire immediately after the conduit is run)?
Trades may color up plans in order to show their desired workflow, what can be completed, how long it takes, and under which assumptions. It is also important to understand the set of potential options for a trade, even though some may not seem optimal from their perspective. This allows for a set-based approach to developing the phase schedule. Each trade’s set of options can then be tested against the sets of options available to other trades, so as to develop a combined plan that is better for the project as a whole than could have been obtained had each trade individually offered only their most-preferred option, or had the GC pushed a schedule on the trades to comply with.
The trade representative in the conversation must be able to provide this level of detail, e.g., the foreman able to commit to doing the work. The benefit to planning early with these details is that people develop deep understanding of both their production capabilities and the resulting production plan from the collected information.
Step 2 - Zone and Takt time Definition
Zone and Takt time definition relate to one another because the duration required to complete an activity is dependent upon where and what needs to be built. Zones are defined in three ways: (1) Improving upon zones already established in a previous work phase, (2) Using the data gathered in a holistic manner (i.e., all the trades are considered when creating the zones), or (3) designing the zones to best satisfy (and then improve upon) the work of one trade because it is evident from data that their work will be the “bottleneck.” This initial set of zones is the starting point for iteration.
Step 3 - Trade Sequence Identification
Given a set of zones, the trade sequences may be obtained through pull planning and working through the construction documents as a team. When identifying the trade sequence it is important to identify and document the specific requirements each trade has in order to correctly hand off zones from one trade to the next.
Step 4 - Balancing the Plan
Balancing the plan occurs in a rough-to-fine fashion. From the proposed zones it is now possible to refine the activity durations for each trade. It would be rare if all trade activity durations were perfectly balanced through every zone from the beginning. Typically durations will vary through the zones. Once the variation is known, the production team can begin to balance the production.
The production team has several methods to balance the workflow and design the production system. The team can iterate upon the zones. If the zones are consistently uneven across the trades, the team can redesign them. Ideally, the project team can change the actual design if it is early enough to improve production. Zones may be unbalanced due to the nature of what is being built (e.g., an operating room will contain more work than a standard patient room). As such, some trades may have to leave out certain work and perform it “off Takt”. The team can also revisit the work methods, trade scope (providing the contract structure enables money to flow across boundaries), and restructure the trade sequence in order to balance the work. Perhaps a trade can (individually or jointly with other trades) prefabricate more work, and reduce their field installation times to meet a lower Takt time. The trade sequence could also change by splitting a trade activity into multiple tasks (e.g., split electrical conduit installation from pulling wire) and enable a faster Takt time. The overall schedule then shortens because a reduction in Takt time scales across the number of zones the trades move through.
Step 5 - Production schedule finalization
Finalizing the production schedule requires validation, i.e., every trade needs to ascertain that their sequences are feasible and that they can perform the work in each zone to which they are assigned in the given Takt time.
These are the five steps to Takt time planning. Gather the data, identify a potential takt time and set of zones that can satisfy the project demands, understand the necessary sequence, balance the plan, and finalize the schedule. The steps are quite iterative and it would be rare to get it all right from the beginning. By working through the steps as a team the result is a schedule that everyone should understand, everyone believes in, and will meet the demands of the project.
1. Frandson, A., Berghede, K., and Tommelein, I. (2013). “Takt time planning for construction of exterior cladding.” Proc. 21st Annual Conference of the Int’l. Group for Lean Construction. (IGLC 21), Fortaleza, Brazil.