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The CPM System is Broken. It’s Takt Time.

by Adam Hoots on

Construction projects are inherently complex, requiring careful planning and execution to ensure success. The most common scheduling method in construction is known as the Critical Path Method (CPM) and it’s broken. This scheduling method has proved itself unsuccessful on vertical construction projects time and time again. CPM was originally created for Dupont Chemical while attempting to find ways to reduce the costs associated with plant shutdowns and restarts that were being caused by inefficient scheduling. This practice was adopted by construction in 1966 and has not been improved upon since it was developed in the 1950s! With the complexities of today’s world, it’s absurd to think that the construction industry’s scheduling systems have not improved much over the past 70 years! In addition to nearly 70% of all construction projects being past schedule, there are several other reasons why CPM is not the best approach for scheduling all construction projects.

There have been some wonderful tools such as The Last Planner® System and Scrum that have been developed to help project teams better communicate the CPM Schedule; however I believe it is past the time for a full scale renovation to the way construction projects are scheduled. This article is intended to challenge the status quo on how the construction industry is currently scheduling projects in hopes that someone will be brave enough to help lead the change with Takt Planning and Takt Construction.

Takt planning is a Lean production planning and control method that breaks down work into smaller units and sets a constant pace for completing them that aligns with customer demand. Takt planning emphasizes collaboration, continuous improvement, and the reduction of waiting time for workers, making it a more effective and efficient scheduling approach than traditional Critical Path Method (CPM) scheduling. Takt Planning allows the project team to see the entire schedule on one page with simple logic, helping to visualize the three (3) types of flow: trade flow, workflow, and logistical flow!

Production Laws

To understand construction production, you must first understand the difference between resource and flow efficiency. Resource efficiency is the ability to keep resources busy and/or active. Flow efficiency is the ability to keep value or the ‘flow unit’ flowing through your process. Once this concept has been established, one would be wise to study the production laws from the book titled:  This is Lean by Niklas Modig and Pär Åhlström. Little’s Law, Kingman’s Formula, the Law of Bottlenecks, and the Law of Variation are all important concepts in the context of Lean production, and they should be first understood prior to attempting to understand why Takt planning is superior to Critical Path Method (CPM) scheduling for vertical construction projects.

  • Little’s Law  states that the average number of items in a system is equal to the average arrival rate multiplied by the average time in the system. In the context of construction, this means three things: 1) Work in small batches, 2) Limit Work in Progress (WIP), and 3) Finish as you go!
  • Kingman’s Formula, which is used to calculate the average waiting time in a queue, can also be applied to the construction context. In the context of construction, workers may need to wait for other tasks to be completed before they can begin their work. Kingman’s formula takes into account resource utilization rates, and variation in order to accurately predict cycle times.
  • The Law of Bottlenecks  states that the capacity of a system is determined by the capacity of its bottleneck, or the part of the process that takes the longest. In the context of construction, bottlenecks can occur when certain tasks take longer to complete than others or when certain resources are in short supply. Note: There will always be a bottleneck, even after you solve the first bottleneck. The trick is to solve the bottleneck and then march the remaining process to the beat of the bottleneck.
  • Finally, the Law of Variation  states that every process contains variation, which will likely lead to unpredictable outcomes. In the context of construction, variation can occur due to factors such as weather delays, equipment malfunctions, or changes in customer demand. The longer you allow variation in your process, the more variation that will occur.

The current CPM scheduling practices do not align with these production laws and oftentimes will steer people away from following these productions’ physics, which leads to further delays and inefficiencies. Takt planning and construction, on the other hand, forces teams to visualize the production laws and have tough conversations before roadblocks arise in order to focus the team on flow efficiency. All of this is done on a one page and easy to understand document. When construction management teams are managing schedules utilizing the CPM method, there are a few additional common issues that are responsible for the noted schedule overruns:

  • CPM scheduling can be complex and difficult to understand for the workers doing the work which leads to errors, confusion, and rework.
  • Work will typically start because the schedule says to start, regardless of the status of predecessor activities, this increases WIP and slows down throughput.
  • CPM scheduling focuses on individual tasks rather than the overall production process, leading to siloed thinking and inefficient use of resources.
  • CPM scheduling creates a false sense of certainty and control, leading to overconfidence and complacency among project team members.
  • CPM scheduling can create a false sense of progress based on the completion of individual tasks, rather than the overall success of the project.
  • CPM is inflexible and unable to adapt to change in project scope or unexpected challenges.
  • Typical practice at the end of a project is to break or hide logic and stack trades, this increases our WIP and slows down our throughput
  • Flow and bottlenecks are hard to recognize in a CPM schedule
  • CPM relies heavily on software and technology
  • CPM schedules by definition have zero float. The most critical chain of activities with no buffer. If projects are scheduled with no room for variation, they will never be successful.

Overall, Little’s Law, Kingman’s Formula, the Law of Bottlenecks, and the Law of Variation are all relevant concepts in the context of construction scheduling, and they should be used to understand why Takt planning and construction is a more superior method than CPM scheduling. By breaking down work into smaller, more manageable units, reducing waiting time for workers, optimizing the flow of work, and allowing for greater flexibility in response to variation through the use of buffers, Takt planning and construction can help to improve efficiency, reduce waste, and increase productivity on your construction project.

Takt planning is the first part of the equation. Once the Takt plan has been established, it’s important to note that the entire project must operate in takt, on takt! Our team refers to this as Takt Construction and should be considered when executing a Takt plan.  As famously noted before, plans are useless but planning is everything! Command and control in the field while using takt construction is where projects will ultimately succeed after the schedule has been communicated in a Takt format. Takt Construction will be issued in a future article.

How many times have you been on a project and it’s been in really great shape, until the last two months?! This has got to change and it begins with recognizing Takt planning as a superior method to managing construction project schedules in concert with The Last Planner® System and Scrum. Takt Planning and Construction aligns well with the production laws that govern productivity, helps to reduce waste and increase productivity, and promotes a sense of teamwork, transparency, and collaboration among workers. As a long-time practitioner of Lean construction, I believe that Takt planning is the essential scheduling improvement that should be made by the construction industry. By adopting this approach, you will be helping to create a more efficient, productive, and enjoyable workplace for trade workers and improve the quality and speed of construction delivery for your clients!

About the author:

Adam Hoots, Construction Scheduling Professor at Clemson University and Lean Shepherd at Construction ACHE Solutions, has 21+ years of experienced leadership developing large scale construction projects. He has primarily built high-tech, life science, clean rooms and laboratories with Whiting-Turner, DPR and Langston Construction. Adam’s passions include building, learning, and sharing knowledge obtained throughout his career. With a ton of energy, Adam will help you and your team develop capabilities to see as a group, know as a group and act as a group!

Image credits to This is Lean, LeanTakt, and Elevate Construction IST.