A Gantt chart is a bar chart used to illustrate a project schedule, that includes some milestones and it is not as detailed as a full critical path method (CPM). It normally includes start and end dates of activities and a summary of activities of a project but not as complex and without the ability to include resources or materials.
The activities are pulled from what is usually called the work breakdown structure (WBS) of a specific construction project. Gantt charts serve as an excellent tool to show updated schedule status using actual complete shadings and vertical lines representing the actual date.
Gantt charts sometimes are prepared to show precedence activities and following activities and their relationships and it is the simplest form of a project schedule. A Gantt chart is the right tool if you are looking to provide an overall summary of the project schedule without major details.
Gantt Chart Advantages
Although simple in its composition, a Gantt chart offers the following advantages:
- Gantt charts can be used to represent the phases and activities of a project in a very simplistic visualization.
- It can be useful to indicate the critical points on the chart with bold or colored outlines of the bars.
- An updated Gantt chart helps manage the project and head off schedule problems.
- Computer software can simplify the process of updating a Gantt chart.
- You don't really need specialized software to build a Gantt chart as it can be easily prepared using Excel or similar software.
What Are the Drawbacks of Gantt Charts
Gantt charts can also have some limitations and might not be useful in some circumstances. There a few other issues as well:
- A Gantt chart is not recommended to define the work breakdown structure and the scheduled activities at the same time.
- Normally, when the project has more than 30 activities, it might not be the best tool, instead, focus on putting together a CPM.
- Gantt charts are not useful if they are intended to display information.
- Gantt charts do not represent the complexity of a project.
- Horizontal bars of Gantt charts misrepresent the actual resource requirements of a project.
- Gantt chart with percent-complete shading may actually miscommunicate the true schedule performance status.
When to Use Gantt Charts
Gantt charts have a variety of uses among construction professionals. Gantt charts must be used under the following circumstances:
- To communicate the plan or status of a construction project
- To monitor tasks within a project
- When putting together a simple proposal for a small project
- To instruct at a high level the sequence and duration of specific tasks or process from a construction project
- To demonstrate which tasks depend on the completion of previous tasks
How to Build a Gantt Chart
The basic procedure must be followed to build a Gantt chart.
- Identify the steps or activities needed to complete the project.
- Identify milestones within the project.
- Identify the expected time required to complete each task.
- Identify the sequence of tasks and the order of precedence of tasks.
- Draw a horizontal time axis on the bottom of a page.
- Select a proper time scale to represent the length of tasks.
- Prepare a column on the left side of the paper; write down each activity and milestone of the project in their corresponding order of occurrence.
- For activities or milestones that occur at a specific point in time, represent them using a diamond under the time the activity must happen.
- Activities that occur over a determined period of time draw horizontal bars, or an empty rectangle starting from the first day the activity will take place and finishing the day the activity ends. Do not fill inside the rectangle.
- Each activity or task must be listed in the Gantt chart.
- Fill up the diamond or the rectangle as each activity is being performed.
- Use a weight or plumb as a vertical marker to illustrate the actual time and progress of the project.
Gantt Chart Considerations
Gantt charts are also modified with additional columns showing details such as the amount of time estimated to perform each task, how many resources are needed to complete each activity and/or the person who is responsible for executing the activity.
Specific meetings or reviewing processes are not recommended to be listed on a Gantt chart because they might occur over a long period of time. Gantt chart will transmit a clear idea to construction professionals about what must be done to complete a specific task and can promote a healthy scheduling process.