Defining terms
The benefit and ability to manage float should always follow the responsibility of managing and meeting the schedule. It is important to know the associated terms—total float, free float, activity float, and project float—because they all carry different meanings.
The Project Management Institute’s (PMI’s) Lexicon of Project Management Terms defines free float as:
The amount of time that a schedule activity can be delayed without delaying the early start of any immediately following schedule activity. [It] is calculated by deducting the early finish time of the activity from the earliest of the early start times of its successors.
The same resource defines ‘total float’ as the:
total amount of time that a schedule activity may be delayed from its early start date without delaying the project finish date, or violating a schedule constraint. [It] is calculated by deducting an activity’s early finish date from its late finish date.
In the past, various other types of float have been described, including ‘start slack,’ ‘end slack,’ ‘free float early,’ ‘free float late,’ and ‘independent float.’ Current use tends toward ‘slack’ and ‘float’ being interchangeable terms, and only ‘free float’ and ‘total float’ being calculated.
One of the primary uses of float in scheduling is to smooth or level resource demands. All resource leveling options cause float to change. Generally, float is consumed to allow some work to be delayed to remove peaks in the resource demand curve—occasionally, additional float is created in some parts of a schedule by the resource leveling process, shifting the overall completion date to a more realistic and achievable time. Effective resource leveling is a highly skilled process that requires far more than simply selecting an option in one’s scheduling software.
The astute project manager must have a detail plan to control float. When dealing with internal projects where there are no formal contracts, it should be treated as a valuable resource to be actively managed by the project team. It is not ‘free’ to squander early in the project, but rather is available to balance resource demands and overcome problems. The approach should be similar to the management of buffers in the CPM methodology.
In contractual situations, the management of float is controlled by the contract. This documentation’s drafters, and the lawyers, should give active consideration to the best way to manage float for the desired outcome. Most case law suggests float is a project resource available to be used by both parties, but this is not always the best option.
Regardless, when it comes to the float, each project manager must check specifications as to the use of any of the CPM Schedule’s 3Ms—manage, massage, or manipulate.
Norman F. Jacobs Jr., CSI Emeritus, CPE, AACE, ASPE, IIE, PMI, SAR, is a principal at Jacobs Consultant Services, which offers cost management, schedule control assistance, project management, and claims preparation/negotiation. He has also served as an arbitrator, owner’s representative, and expert witness in arbitration and court involving multi-million dollar projects. Before creating his current organization, Jacobs provided design-build, construction management, and general contracting for developers, government agencies, and private clients for more than 30 years. He has served as the president of the Construction Specifications Institute (CSI) Richmond Chapter, chaired the Virginia Associated General Contractors (AGC) Documents Committee, and been a long-time member of organizations including the Project Management Institute (PMI) and the American Society of Professional Estimators (ASPE). He can be contacted via e-mail at jcscpm@aol.com.
