David Ross Associates LLC - 900 Industrial Rd. Ste. E, San Carlos, CA 94070
  • 900 Industrial Rd. Suite E
  • San Carlos, California 94070
  • P:(650) 593-2001



Making Short Work of Diagramming the Critical Path

By David Ross


The following is a reprint of an article that appeared in the San Jose Mercury News on Sunday, May 26, 1985 - when David Ross was a vice president with Jack & Cohen Builders Inc. in Palo Alto. At that time, his company was at the cutting edge of using technology in construction projects by running "project management" software on an Apple Lisa computer.

David Ross - 1985

Building is expensive, with costs of all kinds climbing to uncharted territory. Contractors must be efficient in controlling expenses and construction schedules in order to compete and survive. For the construction industry, then, the micro-computer revolution came just in time. One of the most useful computer applications for getting projects done on time and on budget is "project management" software. Building contractors are required to perform quickly, but the rules, agencies and fates that oversee every project can frustrate the best-laid plans.

Some method must be employed to plan a construction job from one end to the other - from design to occupancy. Every important part of the work has to be identified, analyzed and scheduled in advance. It is also crucial to know how various parts of the work effect each other. Also, products incorporated in the construction may have long lead times, and sometimes cannot be installed on time. What other parts of the job will that affect and how much? Fortunately, sophisticated scheduling tools have been developed to help solve these riddles. The main idea behind most methods is to discover the "critical path" for a project.

That path is the sequence of events allowing the least waste of time, money or other resources. It shows which parts of the project need the most attention. The idea of critical path scheduling sounds simple. Taking a closer look at it, though, this approach requires a lot of work. The project must first be divided into a number of "tasks" that are easily tracked. The smaller the tasks, the more useful the schedule. Stating a task such as "build three-story office building" doesn't help much. It's better to be more explicit by defining specific tasks such as "paint door frames in offices 101-131."

Every task depends on the completion of at least one other task or a "milestone." Milestones are events instead of jobs, as in "first floor complete" or drywall nailing inspection O.K." In order to make critical path scheduling work we must discover the immediate predecessors for each task. When that has been done, the list of tasks can be turned into a picture of the work to be done.

Putting all the information down on paper in the form of boxes, circles, and interconnecting arrows - called a network diagram - is a good way to keep it handy. A good draftsperson would take a few days to draw one of these up for a medium-sized construction project. With a little more work, the diagram becomes a schedule. However, with a computer system, this work only takes a few hours. Another major advantage to computerized project scheduling is that changes can be recalculated instantly. With the manual method, changes could take hours or days of work.

network diagram

One of the first things that catches most people's attention about these diagrams is that several paths or branches go on a t the same time, independent of each other. That is actually one of the reasons for doing this exercise. If the plumbing crew and the electricians can work simultaneously, for example, some time might be saved.

The final step in making the diagram ito a schedule is determining which of the paths is "critical." With a given starting date for the project, the time required for each task is added in. The path through the network that takes the most time is the critical path. The reason that the critical path uses the most time is that all the tasks on that path must be tackled in order. A delay in performing any of those tasks causes a delay in the finish date of the project.

Most successful contractors use critical path scheduling for their projects. Clients and architects frequently require such a schedule before the construction begins. It isn't hard to see how this tool can help control both costs and completion dates in a very complicated, costly industry. The main drawback, though, is that every time a change is required the old diagram becomes obsolete and has to be recalculated. As computing power has gone down in price, programmers have become more clever in reducing critical path programs to fit microcomputers. Now, almost any contractor can afford the hardware and software required to schedule small and medium sized projects.

In our company, critical path scheduling was done manually and was mainly viewed as a contractual requirement. It was too expensive to recalculate during the job when changes came up in order to best plan the remainder of the work. Instead, it was done once and pretty much ignored. However, now that we've computerized this process, we consult the critical path schedule and modify it as necessary. It's made a big difference in our ability to complete projects on time and within budget. After examining several scheduling programs available in 1984 we chose LisaProject (older sister of MacProject) for our Apple Lisa system. The program is sophisticated enough to handle projects with more than two thousand tasks. Training time has been minimal - each of our project managers and superintendents was able to produce a simple critical path schedule at their first session. Most had no previous computer experience. LisaProject's real strength is the graphic presentation of all the information needed to manage the project at the job site. The network diagram may be formatted by the user to make the schedule as easy to read as possible. Several displays are available, including charts and cash flow tables.

Recently we used LisaProject to demonstrate to a client that their construction project could be shortened by two weeks with only a small cost increase, but that taking out three weeks would have added nearly 10 percent to the overall budget. This is only one example of how we've saved our clients time and money with this system.




David Ross Associates LLC
900 Industrial Rd. Suite E
San Carlos, CA 94070
Phone: (650) 593-2001