It’s tempting to make budgets the most important aspect of construction projects, but that means you overlook the importance of proper scheduling. A poorly crafted construction schedule will always wreak havoc on the budget. Ever since construction entered the modern age, people have tried many methods and tools to create construction schedules that work. In this article, we’ll discuss several of the most common practices and their pros and cons, starting with the CPM schedule method.
The CPM Schedule Method
A critical path construction schedule is a logic network. It shows the relationships each activity has with others. It works well for many projects and truly excels at well-scoped and carefully planned projects. A CPM schedule uses mathematical calculations to predict when people will complete their work. Ultimately, it predicts the project’s completion based on a critical path.
How the Critical Path Construction Scheduling Method Works
Critical path scheduling views the project as a network of tasks, activities and resources. This method shows all activity relationships relative to the longest path in the network going from start to finish. If you know what ‘float’ is (the time you can delay a task without it affecting another task), then the critical path is the path with the least amount of float.
Look at your schedule, and highlight all the activities that have no float and must finish before the next activity starts. Then draw a line connecting them. You’ve just found the critical path. You probably can’t do this easily when you have a project with 20 or more activities, so CPM scheduling software could prove useful.
When CPM in Construction is Helpful
The critical path method shows you the longest path in the project’s activities. It also makes it easy to visualize dependencies among activities to get the best mix of resources. You’ll find it easier to monitor project tasks and control costs. Thanks to knowing the project requirements well before completion, you can operate more efficiently. You can see chokepoints better, and you can respond to small changes more quickly. The CPM makes it easier to see if the project is on track.
Disadvantages of the Critical Path Method in Construction
The critical path method also has disadvantages that arise mainly from its complexity. You have four steps in creating a CPM schedule, and each step has variables that can affect accuracy.
For example, the first step requires you to break down the work activities. If you don’t accurately consider all aspects, variables will skew assigned times. So, a CPM schedule doesn’t arise just from the estimator’s work breakdown structure. Another step is to set the duration for each activity. Get it wrong, and you might end up getting a wrong critical path.
The more paths with similar lengths, the more difficult it is to confirm the critical path.
One way to mitigate this risk? Ensure you communicate your schedule properly. Click here for some tips.
You also must figure out the logical relationships among the activities. In this step, it is easy to mix in constraints, possibly reducing accuracy in the calculations. Finally, you draw the network and do the calculations.
The critical path method can get too complex when you apply it to big, complicated projects that aren’t defined well. CPM also doesn’t respond well to major changes in scope once the project is underway. The more paths with similar lengths, the more difficult it is to confirm the critical path.
Popular Standalone Construction Scheduling Software
You’ll find many project scheduling cloud options, but the two desktop applications most prevalent in construction are Microsoft Project and Primavera P6 Professional Project Management. Both solutions use a CPM approach to scheduling.
Microsoft Project — Pros & Cons
The biggest benefit of MS Project is that it is mature and has multiple tools and options for both setting up and managing a schedule. MS Project interfaces with both Office 365 and Sharepoint. The Sharepoint version is MS Project Server. The software is reliable and well supported, making it easy to get help whenever needed. The desktop version doesn’t require an internet connection, and it comes with templates to reduce the time you spend setting up a project. MS Project works well for portfolio management as well. You can use your MS Project schedules with Procore.
The application is Windows only and requires a desktop installation, even when opting for the cloud version. It is not an application that people will just pick up and run with—it takes a lot of learning. It’s also expensive, so you need to consider your usage level and whether your people can get the most from it.
Primavera P6 — Pros & Cons
This is a top choice for scheduling in the construction industry. It is robust enough to handle up to 100,000 activities. Along with its resource and cost management options, its Gantt charts and reporting, there is not much to want.
P6 allows four relationships between any two activities, and you can divide activities to improve reporting. The newer 64-bit version can use more RAM to improve processing and speed. You can use your Primavera P6 schedules with Procore. You can also get an Enterprise Project Portfolio Management—a “solution for globally prioritizing, planning, managing, and executing projects, programs, and portfolios.”
On the downside, it’s Windows only and has a steep learning curve. In fact, many people make a living offering P6 training. Some say the interface looks dated, and the reporting output isn’t very appealing.
Resource-Oriented Construction Scheduling
You might turn to a resource-oriented construction schedule when an aspect of your project calls for a limited resource in high demand. You might have just one excavator, or maybe you have specialized work requiring a specialized crew. Using this technique, you reduce the time the resource is idle while also minimizing the waiting time for the resource.
Resource Scheduling Pros
This construction scheduling technique can help with bottlenecks and can assist schedulers to see other options they might have missed.
Resource Scheduling Cons
It’s complicated to use due to the math required.
Gantt Charts for Construction Scheduling
Based on bar charts developed by Henry L Gantt in 1917, the Gantt chart represents a construction schedule by showing the project’s activities in a line of bars scaled to time. You list the work breakdown structure on the left side of the chart, dates along the top, and activity durations as horizontal bars rising from a time scale at the bottom. In their original form, there was no linkage between activities.
The charts created by today’s scheduling software, however, usually show linkages like start-to-finish, finish-to-start, finish-to-finish, and start-to-start. You can include resources, and the bars will have different colors to represent lag and float.
Gantt charts excel at simplifying schedules. Once people understand what they’re looking at, they can quickly grasp what’s going on. They can easily see when their portion of the project begins and ends, and can tell how much time they have for completion at a glance. People don’t need technical backgrounds to get value from these charts, which convey the building plan clearly. Gantt charts offer both a very detailed look at the schedule and a wider view, depending on the detail you want to see.
People don’t need technical backgrounds to get value from these charts, which convey the building plan clearly.
Computer-generated charts also might include crew sizes, work package descriptions, and safety requirements. They can even show percentages completed and budget information.
Because Gantt charts are so easy to construct and understand, people will often load them up with too much information and detract from their core strength—simplicity. Saleh Mubarak points out in “Construction Project Scheduling and Control” that Gantt charts also don’t show the logic behind what’s happening. For example, you can’t tell why an activity started when it did. Was it a management decision, a resource constraint or something else? Gantt charts only work well for large complex projects if you break them down to show smaller subsets of the entire project and include summary versions.
The U.S. Navy, Lockheed Corporation and Booze Hamilton developed the Program Evaluation and Review Technique to overcome huge delays in submarine building during the 1950s. While CPM is deterministic (you set completion dates for activities), PERT is probabilistic (you assign a likelihood to anything that has a date). This recognizes the uncertainties inherent in projects. Durations vary, so PERT assigns a time range to activity completions. Construction planners often mistakenly refer to precedence networks having deterministic CPM calculations as PERT. But, those are precedence network diagrams.
PERT can work well in construction if used on projects where new or experimental methods and materials prevail. For instance, for a building project using 3D printing or one designed to overcome unknowns through trial and error.
PERT follows a single path, so schedulers must analyze all paths for the highest uncertainties. This is complicated and time-consuming. Coming up with the required three durations for activities is sometimes difficult. When updating the schedule, you can easily skew the logic which some schedulers might do to hide a poorly planned schedule.
All in All
More than anything else, the tool you use to schedule your construction project must depend on the project’s needs. When your choice is based on the scheduling tool’s fit, you’ll have a better chance of making a schedule that responds to the project budget and helps you avoid delays