CPM Scheduling Will Work For Your Project
Don L. Short, II, FCPE

Reprinted with permission of the
American Society of Professional Estimators

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The first attitude encountered on a project involving Critical Path Method (CPM) scheduling is often times, "Do we have to?" This is one attribute shared by owners and contractors on a large majority of projects. Unfortunately, this attitude can cause substantial problems for the project. There are numerous good reasons for preparing a CPM network diagram on most projects - ‘because it’s required by the contract documents’ is not one of them; ‘because we have to’ is also not a reason.

The most important reason for developing and maintaining a CPM is to manage the work. Side benefits to this are improved communications between the prime and subcontractors and between the owner and the contractors. A CPM can be useful for progress payment requests, determining potential delays to the work, determining alternative sequences, and many other uses. To make the CPM useful, the information must first be input (presuming it’s a computerized schedule in these days) and then updated on a regular basis.

While the prime contractor is responsible for the preparation of the schedule, the preparation of the schedule must involve the subcontractors and suppliers. The schedule must incorporate the owner’s requirements and the specifics of the project, not general assumptions.

INITIAL CPM SCHEDULING

The size and complexity of a CPM schedule is dependent upon the size and complexity of the project to be managed, for the schedule is analysis and management of the work to be performed. If a project is being performed with phased construction, the schedule should be prepared in accordance with the phasing requirements on the work scope. If a project is of a less complex nature, the CPM should be prepared to reflect the conditions and simplicity of the project.

The information for the initial CPM diagram comes from many sources. The most important of these is the estimate. This document provides the work scopes, manpower levels and duration’s, craft types and the value of the activity being performed. While a person preparing the schedule can glean a lot of the required information from the estimate, it is very helpful to have the project estimator involved in the preparation of the schedule. The estimator is the person most knowledgeable about the project conditions and the planned method of performing the work at the time schedules are usually prepared. In addition to this, the project manager and supervisory personnel for the project must participate in the development of the schedule. They are the ones who have to use it and live with the results.

Another source of information, critical to the successful application of a CPM diagram, is the contract specifications. This document identifies required submittals, approvals and other contract requirements that must be fulfilled prior to initiating work at the project site. Some of these include safety plans, QA/QC programs, welder qualifications and milestone dates.

The information developed from the estimate and the specifications are important to having a complete CPM network for the entire project. Activities developed from the specifications eventually lead to installation activities contained in the estimate.

In today’s rapidly evolving technological market, software for scheduling is available at very reasonable prices. The lowest priced software can handle one method of scheduling with up to several hundred activities. More expensive software can handle unlimited activities, both methods of scheduling, and a host of other features. Prices range from $500 or so to in excess of $4,000 for personal computer applications (80486 and higher processors). Many application packages are discounted from list price, so do not forget to ask about discounts.

While the software will speed the process, there is no substitute for an experienced scheduler in developing the schedule and performing the updates to the schedule. A "computer jock" who can perform data entry and make the software "sing" is of no help if the schedule is put together with incorrect relationships.

By using computers for scheduling, the scheduling effort can be performed with more thought and less of the tedious work. Examples of this include having the computer calculate early and late dates, using it to plot the actual diagram, having it printout the required reports and performing recalculations of the schedule in a very short period of time. It is highly probable the use of one of the common scheduling software packages will pay for itself in time savings on the very first project.

In addition to having the above information and scheduling software, it is helpful to have standard forms for preparing the diagram of the project. There are two primary methods for performing CPM diagrams. The first one is the Arrow Diagram Method (ADM) This consists of nodes and activity lines. The other method is the Precedence Diagram Method (PDM). This method uses boxes and lines. Each method will enable the user to more than adequately manage a project. The important consideration here is to use one of the methods, not to ignore either method and resort to a bar chart or no schedule at all on the project.

The forms, preprinted with the scheduling method to be used on the project, are invaluable tools for developing the schedule. Using a pencil and eraser (big one) in conjunction with the forms allows the planning, revisions and almost final sequencing to be performed on the logic, before it is entered into the computer. By using preprinted forms, supplier, subcontractor, prime contractor and owner activities can be developed and integrated into a comprehensive schedule. Two types of forms should be used for developing the schedule. The first one would be used for the submittal development. The second one would be used for the installation activities.

Determining the submittal requirements for a project involves reading the general, special, and technical specifications. These list which items are to be submitted for approval or for information only. Where a submittal is not addressed in the specifications, activities are usually not developed. When reviewing the specifications for submittals, the estimate and quotations for the project must be available. Submittals should be developed and referenced to the specifications section and party responsible for the submittal and/or approval, as a minimum.

Each submittal for approval will require a minimum of three activities in the submittal portion of the schedule. The first activity is the submittal by the prime or subcontractor. Next is the approval of the submittal by the owner. The final activity in this sequence is the fabrication and/or delivery of the materials. When the submittal involves shop drawings or coordination drawings, typically for a mechanical contracting firm, the activities for one submittal can involve relationships with additional activities for the submittal’s sequences.

A submittal for information only will typically require two activities on the network diagram. These activities consist of the submittal and the fabrication and/or delivery of the materials.

It is not necessary nor desirable to identify each component of the project for submittal. This is generally too much detail and unwieldy for managing the project. Items for submittal should be grouped by specification section and vendor when possible. For instance, if there are ten air handling units with eight from one vendor, they should be grouped as one submittal. The other two air handling units, if coming from one source, can be grouped as a separate submittal.

While grouping by the above method, there are instances when materials need to be separately identified on the schedule. An example of this is for long lead delivery items or items not required in the same time frame. There may even be a case where a submittal is not required for a long lead delivery item. If this should occur, an activity showing the procurement of the item should be included in the schedule so that the procurement can be monitored.

Each of the submittal sequences should show the number of days duration and responsible part, as a minimum. In cases where materials are paid for upon delivery to the site or a secure warehouse facility, the cost of the materials should be included with the fabrication and delivery activity. When shop drawings and coordination drawings are a part of the submittal process, costs should be included in these activities, whenever possible. Many owners will object to the inclusion of funds for this work. However, since costs are being incurred, they should be recovered for the activity being performed.

Each of the submittal, approval, delivery sequences will lead to one or more installation activities. These activities are developed from the estimate and must be coordinated with the submittals. When and estimate is prepared, it is in conformance with the project requirements. This not only applies to the specifications, but to the physical conditions under which the work is to be performed. This may include different floors, work areas or phasing of the construction. It can involve intermediate milestones or special sequencing procedures for the work.

Installation activities require more information than is included with the submittal activities. This information includes the responsible party, craft types and durations, area (i.e. floor number, zone, etc.), phasing, dollar value and other information pertinent to the management of the project. There may be special sort codes used for printing and plotting of selected activities. The determination of what to include with each of the activities should be made prior to starting the schedule and all parties informed as to these requirements.

It is very helpful to establish standard coding to use from project to project for commonly encountered schedule requirements. Examples of this would include designating the prime contractor as "PRIM," the owner as "OWNR," the plumbing contractor as "PLBR" and the electrical contractor as "ELEC." In this manner, a print or plot request could be made for any activities attributed to the specific contractors. Further coding of the schedule on a floor by floor basis could further refine a report to select work activities by all contractors needed on the 2nd floor or by one of the contractors on the 2nd floor. While the possibilities are numerous, the project needs will dictate the practical application of much of the schedule information.

Sequencing of the work will follow the project needs. While there are readily identifiable steps to every work activity on the project, the number of activities and their relationships should be in conformance with the complexity and size of the project. An example of this could be the placing of concrete for a sidewalk. If the sidewalk area is small, say four feet by one hundred feet, it is more practical to have a few activities relating to this work. If there are large amounts of sidewalk area, say 20,000 square feet, more activities should be used to manage the work.

When determining work activities, logical breakpoints in the work should be determined. This is not only applicable for the contractor performing the work, but also when interfacing with a different contractor. A prime example of this would be with drywall, painting, plumbing and electrical contractors. The interface points require coordination so that work can proceed at its best pace, with minimal interferences between the different contractors. A few of the normally encountered interface points for the work activities with these contractors include:

1. Wall layouts need to be completed prior to roughing in the plumbing.
2. Metal studs must be in prior to running electrical conduit.
3. Gypsum board cannot be placed on both sides of the wall prior to running the conduit, however one side can be installed.
4. Painting and/or other finishes should be performed prior to installing the plumbing.

When preparing the relationships between activities, caution should be used in establishing the relationships between the work. Several relationships can be established for many activities on the CPM diagram. While including redundant relationships will not necessarily hinder the management of the project, as few as possible redundant relationships should be included. This makes for easier updating and less time in the original data entry.

The development of the work activities should continue for the balance of the project by using the preprinted forms. Once the schedule is substantially completed, it is time to begin the data entry process. With the schedule at this point, the activities need to have numerical designations. With the ADM method, this involves two numbers. The first is the I node number and the second is the J node number. The PDM method uses one number. These numbers can be numeric or alphanumeric for most software found in the market. When numbering the activities there is a protocol or methodology to follow. Activities are numbered from left to right and top to bottom of the page. The numbers of succeeding activities are higher than the preceding activity (preferred but not mandatory). Do not use consecutive numbers, leave room for additions during the updating of the schedule (i.e. skip numbers).

Having numbered, entered and proofed the data, a series of plots and reports can be printed for distribution to the parties for final adjustments and/or corrections. It has been found to be particularly helpful if reports and plots are furnished for this task. Once the comments have been returned, agreed upon and corrections made, the schedule is ready for submittal to the owner for approval. With approval by the owner, the schedule must be distributed to all members of the project for their use.

 

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