The Bar Chart, or Gantt Chart, is a visual presentation of the sequence of construction events for your new home. As you can see from the example below, the Bar Chart is basically a grid sheet with the construction activities listed vertically in the first column and a time line across the top in the first row. The time a particular event (construction activity) is to occur is simply shaded in.
Piece of cake, huh?
By building a Bar Chart like this, you, the owner builder, know in advance when every facet of the job is to begin and when it should be completed. This is a planning function, and is carried out before the job is begun.
With your Bar Chart in hand, you are able to schedule subcontractors and materials deliveries so that the proper sub and the necessary materials arrive when they are needed, which in turn will allow you to save time, money, and hassle.
compared to the critical path method (cpm) diagram
The Bar Chart is a different way of presenting or viewing some of the same information shown in a Critical Path Method diagram (CPM). Take a few minutes to look at our discussion of the CPM diagram here so that you can follow the discussion below.
Click here to see an example of a real Bar Chart for the construction of a home over a twelve week period. Below is a portion of that Bar Chart.
Look at Line Number 8 (Framing) on the Bar Chart above. It shows this activity as being scheduled for nine days (days 14-22).
Below is a Critical Path Diagram showing the same activities as above. You can see that the "Framing" activity is indicated by the arrow with the "20" and "25" circles at each end, and that the arrow indicates that the framing activity lasts from day 14 through day 22.
DIFFERENCES
For some people, the Bar Chart is a little easier to grasp. Notice a couple of differences though.
1. The Bar Chart does not show any dependencies. In the Critical Path Method diagram, an activity (arrow) cannot happen until all of the previous activities (arrows) have been completed. These relationships are not depicted in the Bar Chart. For example, line 13 shows the Cornice, Veneer, & Exterior Trim being completed on day 31. Line 25 shows Drywall starting on day 32. You may think there is some relationship.
But a look at the Critical Path Diagram shows that the two are unrelated. The only things that can be said of their relationship (again looking at the Critical Path Diagram) is that the framing must be completed before either exterior trim or drywall can begin, and that both activities must be completed before the final inspection - for those are the two points in the diagram where their lines diverge and then come back together again.
2. Another shortcoming of the Bar Chart is its inability to show float times very well. On the Critical Path Diagram you will see that setting the prefabricated fireplace and installing the hearth and profile takes four days, and can take place any time between days 23 and 42. The Bar Chart shows activities taking place at their earliest possible time. So the hearth and profile are shown on days 24-26, immediately following setting the fireplace on day 23. Obviously, knowing where your float occurs can give you some flexibility in scheduling the work.
3. Finally, the Bar Chart does not indicate which activities are critical. By looking at the chart, there is no way to tell that a delay in the Interior paint and wallpapering will delay completion of the home - where a delay in the exterior painting will not (as long as the 16 float days between event 25 and event 135 on the Critical Path Diagram have not all been used up).
