Critical Path Method (CPM) scheduling is the development and use of a comprehensive work plan representing the logic behind a construction project through network diagrams. These network diagrams show how the work will be done and are used as a guide to coordinating and managing work remaining in a project.
To have an accurate gauge of what is going on at a job site, CPM schedules must be managed well and built with integrity. Otherwise, unforeseen budgeting and timeline issues will arise.
Industry Challenges with CPM Scheduling
While there are plenty of benefits to CPM scheduling, there are a few common hurdles in the CPM Scheduling process. Some of the common issues we have seen are problems with logic and schedule detail, which are summarized below.
One of the most common problems in creating a CPM schedule is having feasible logic ties. Logic ties show the relationship between activities' start and finish dates. The challenge here is that too many CPM schedules have logic that is not formally thought out, which ultimately affects the legitimacy of the critical path. If a project is managed without an accurate critical path, then it is impossible to determine what is actually driving the project, thus making it also impossible to effectively manage delay.
To overcome this challenge, you need to contemplate both hard and crew logic in great detail to produce a high-quality schedule. It is important to note that just because a project has a high-quality schedule does not mean that the project will not be delayed. As we know, delays are a widespread phenomenon in the construction industry and often arise from things that are way out of our control. This brings us to the next problem with logic: crashing logic.
When someone decides to crash the logic within a CPM schedule, it is usually an attempt to overcome a delay. Crashing logic entails shortening the duration of activities by adding additional resources.
While crashing may offer an avenue to make stakeholders not worry about a delay, it may embed more risk into the project in the long run. Regardless, there are three common ways to deal with delays in CPM scheduling.
- Accept the delay and update the schedule without any changes.
- Understand the delay issues and make modifications based on well-thought-out mitigation strategies.
- Change logic as quickly as possible to “overcome” the delay.
Unfortunately, changing logic by crashing is the most common and widespread across the industry. Crashing logic not only adds cost to the project but also may change the critical path or make the entire plan unfeasible. A feasible schedule is highly important for effectively managing a project, which leads us to the next issue in CPM scheduling: too much or too little detail.
Too Much or Too Little Detail
CPM schedules require that the schedule is created according to activity cost, resources, or durations. However, many schedules have too many activities, which requires more time and embeds risk within the accuracy of the schedule data. On the other hand, some schedules lack critical activities, adding risk with coordination issues and other inefficiencies. Anyway, the sweet spot for me is 500-2000 activities for a project of $20M+, with somewhat of a correlation between the number of activities and project size.
I’ll admit, creating a CPM schedule can be challenging due to the amount of detail and accuracy involved in creating a high-quality schedule. To help overcome this challenge, I have listed some tips for CPM scheduling below.
Tips for CPM Scheduling
- Make scheduling a team effort and utilize an organization breakdown structure (WBS).
- Get buy-in from trade contractors and site teams when creating and updating the schedule.
- Update the schedule on a monthly basis at the least by using the most accurate and current details available.
- Study historical delay issues and resultant mitigation plans at every update.
- Utilize the schedule to help with daily planning, troubleshooting, claims, cash flow, historical record, and resource planning.
- Make sure that higher management is committed to the schedule of the project.
These breakdowns should not deter from the primary advantage of the CPM schedule: its ability to identify the relationships and dependencies between all of the activities within the total project network. The CPM also creates a sort of blueprint that showcases the relationships between both construction and non-construction activities that affect performance.
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