If you don’t use a critical path method (CPM) for your construction projects, you are missing out on the confidence it can instill in your workforce and partners. Most people hate to plan but will heartily appreciate the planning that works. That’s where CPM and other forms of advanced scheduling can help more than just in improving project duration. However, a CPM schedule that’s ill-conceived or poorly updated will not be a great construction scheduling example.
Here’s are four things to watch for as you use the critical path method:
1. Confront missing logic
On the critical path, every activity except the first one has a predecessor, and every activity except the last one has a successor. If that’s not the case in your schedule, you could have missing logic. An activity without a predecessor or a successor effectively breaks the critical path. Using a project start milestone as your first task and a project complete milestone as your last task will provide a way for tasks that don’t have successors or predecessors to link up to the project.
You should also look for constraints that are not contractually required. Adding a constraint to an activity affects the critical path calculation and can affect the schedule negatively. For instance, if a task depends on a piece of equipment, then make getting the equipment a predecessor to starting the task instead of setting a constraint.
You can also inadvertently create a constraint by manually assigning a start or finish date. Assigning a start date to an activity adds a start-no-earlier constraint while assigning a finish date creates a finish-no-earlier constraint. In both instances, you are undermining the software’s ability to calculate the correct critical path.
2. Be brutally realistic
Any CPM scheduler who wears rose-colored glasses is likely not seeing the reality of the build. People naively rely on the best-case scenario only to see the critical path devolve into a highway of heartache. Most construction projects are constantly changing. To be out in front of change, look for all the places in your schedule where change might happen.
Is it really possible the sub who is always a day late will suddenly get the job done early? How many people will it take to offset the productivity loss of one machine going down? What’s the likelihood you can get an inspection on Friday afternoon before a long holiday weekend? These are the kinds of questions you need to ask yourself as you look at each activity and the predecessors to it.
3. Don’t create unrealistic workloads
A critical path in project management gives you all the advantages of advanced resource management. Your scheduling software usually offers three different ways to calculate work, duration, and units when using a task information dialog box. It’s easy to confuse work and duration because they both deal with time.
Work, or effort, is the actual work time needed to complete the task. Assuming you have a workday of eight hours and a task that requires 20 hours of effort, its duration is 2.5 days.
Duration is like calendar time, so the total time allocated to finishing a scheduled task is based on the resources assigned. This ‘total time’ does not include weekends, holidays, and other times when resources would not work on the task.
In most instances, your estimate already has a set amount of effort for each task. So your first pass at creating the schedule is to fit that available effort into the desired project duration. As you assign resources with their corresponding work effort and durations to a new schedule, set the task type to ‘fixed duration.’
Once satisfied with the assignments, switch the task type to ‘fixed work.’ You will see the duration of the tasks change to reflect the realistic effects of changes in resources and work units. This makes the critical path effort-driven and helps prevent scheduling unrealistic workloads.
4. Do accurate and timely updating
Usually, the contract will specify when to update the schedule, sometimes, though, your critical path will be more accurate if you update more often, especially if you:
– are getting scope changes;
– have time and material contracts anywhere in the project;
– have growing risks;
– have activities competing for critical path status;
– have major specifications changes;
– have noted inaccurate completion percentages;
– have had changes in work sequencing.
While your primary goal in updating the schedule is to confirm the critical path still meets the project’s required duration, you can also confirm payments are tracking with the schedule of values. The other benefits of updating the schedule include keeping as-built data accurate, confirming the schedule is in line with the sequence of construction, and identifying new project risks.
So how do you make the updates accurate? You need trusted information. You likely have people reporting how long activities took and percent completed, so periodically check at data for accuracy. Beware of unverified information from new or unknown sources. Do the update when not distracted so you can focus on accurate inputs. Verify all estimated finish dates by comparing past performance and assessing potential risks.
Using a critical path method is easier than ever with today’s software. Let the software do the heavy lifting by using quality inputs and avoiding actions that undermine CPM calculations.