INTRODUCTION project management, resource leveling is defined


The concept of “float” is less than 50 years old. The existence of a “critical path” and noncritical activities (with their associated “float”) grew out of the science of “scheduling” as defined by the Critical Path Method (CPM).

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From the 1960s onwards, the use of “critical path” techniques began to dominate project controls.

The apparent precision of the single duration estimate required for the “critical path” techniques dominated.

This paper will focus on “float” -which is an intrinsic part of all project control methodologies- showing its definition and types and benefits then the repetitive argument of “who owns the float?”.

This collected paper is submitted as a class-work for the MASTER Planning Course in AL-MADINAH Al-MONAWARA.











In project management, “float” or “slack” is the amount of time that a task can be delayed without affecting the deadlines of other subsequent tasks, or the project’s final delivery date.


The simplest way to compute float is to subtract the time you’ve allotted to complete a task from the time the task actually takes. Tasks that have zero float can be considered as part of the “critical path”, because any delay on these tasks means a delay to the project deadline itself.


In order to maximize float, you need to identify your critical path and calculate the amount of float in each non-critical task path. It will help if you visualize the project using a Gantt chart or PERT diagram. With these tools, you can reshuffle tasks and consolidate all of your non-critical tasks into as few task chains as possible. You can then reassign resources and work schedules to focus on the critical chain, and to increase team productivity and efficiency. It may not change the amount of float, but it will get you the most out of those spare hours.

Make sure you revise your float estimates as the project goes on. If one task takes longer than expected, you have the option of using up estimated float from a task further down the calendar. Some project managers add a little bit more float than necessary as a safety measure against unexpected delays.

Of course, there will be circumstances where your project gets delayed no matter how well you manage your float time. Learn from these delays and account for them the next time you schedule a project.


Floatusageonpathsofnon-criticalactivitieshaveaneffectonresources, stackingoftrades,andotherproductivityissues.


Two of the common benefits of the floats are:


1-  Resource Leveling:

In project management, resource leveling is defined by the (PMBOK Guide) as “A technique in which start and finish dates are adjusted based on resource constraints with the goal of balancing demand for resources with the available supply.”

When performing project planning activities, the manager will attempt to schedule certain tasks simultaneously. When more resources such as machines or people are needed than are available, or perhaps a specific person is needed in both tasks, the tasks will have to be rescheduled concurrently or even sequentially to manage the constraint. Project planning resource leveling is the process of resolving these conflicts. It can also be used to balance the workload of primary resources over the course of the projects, usually at the expense of one of the traditional triple constraints (time, cost, scope).

Resource leveling is also useful in the world of maintenance management. Many organizations have maintenance backlogs. These backlogs consist of work orders. Without resource-leveling the organization (planner, scheduler, supervisor) is most likely performing subjective selection.

Resource Leveling on a project.


2-  Delay Analysis:

Construction projects continue to suffer delays. Things go wrong and the project’s completion dategets pushed back, with someone to be blamed for it. In practice, attempts are made to identify the causes of delays and schedules are modified to incorporate revised duration and new project time. The analysis itself is usually complex and can be aided by a computerized approach. Different delay analysis techniques are currently used by practitioners in the construction industry.





1-  Total Float (TF)

Total float is what many of us are aware of, and is commonly referred to as a float.

Total float is the amount of time that an activity can be delayed without delaying the project completion date. On a critical path, the total float is zero.

Total float is often known as the slack.

You can calculate the total float by subtracting the Early Start date of an activity from its Late Start date (Late Start date – Early Start date), or Early Finish date from its Late Finish date (Late Finish date – Early Finish date).

TF = LS – ES or TF = LF – EF


TF = LF – Dur – ES


2-  Free Float (FF)

Free float is the amount of time that an activity can be delayed without delaying the Early Start of its successor activity.

The free float can be calculated by subtracting the Early Finish date of the activity from the Early Start date of next activity (ES of next Activity – EF of current Activity).


If two activities are converging to a single activity, only one of these two activities may have free float.

FFi = min(ESi+1) – EFi

where min (ESi+1) is the least (i.e., earliest) of the early start dates of succeeding activities.

3-  Interfering Float (Int. F)

Interfering float is the time span in which the completion of an activity may occur and not delay the termination of the project but within which completion will delay the start of some other following activity.

Int. F = TF ? FF

4-  Independent Float (Ind. F)

The independent float is a very convenient measure of scheduling freedom. The independent float of activity is the maximum time can be delayed without delaying successor activities, if all prior activities are finished as late as possible. It gives a measure of time available if the worst possible conditions prevail in the predecessor activities.

It also gives an indication of the possible degree of decoupling the activity from the others in the project, hence the name independent.

In other words – it’s the free float of the late dates.

Ind. F=min(ES of the Succ.) – max(LF of the Pred.) – D


5-  Safety Float (SF)

Safety Float is the maximum time an activity can be delayed without affecting the final project completion if predecessor activities are completed as late as possible. This new measure appears to be one of the more useful float measures when scheduling a particular activity.


 It, permits only successor activities to be delayed, not the entire Project.

In other words – it’s the total float of the late dates.

SF=LF – (LF of the Pred.) – D


6-  Remaining Float (RF)

Remaining Float is calculated as the difference between the Late Finish and the Remaining Early Finish.

It’s different than total float when the resource leveling feature is used.


The ‘float’ is the amount of time that non-critical activities can absorb, in excess of their original intended duration, without impacting on the critical path of the works as a whole.

A Contractor may argue that it ‘owns’ the float because, in planning how it proposes to carry out the works, it has allowed additional or ‘float’ time to give itself some flexibility in the event that it isn’t able to carry out the works as quickly as it planned. If there is a delay to the Contractor’s progress for which the Contractor is not responsible, it may contend that it is entitled to an EOT, even if the delay to progress will not result in the contract completion date being missed but merely in an erosion of its float. In addition, the Contractor may want to accelerate the works in order to keep the float in full and claim its costs of doing so.

On the other hand, an Employer may say that the Contractor has no contractual remedy for being prevented from completing the works at any time prior to the contract completion date, and is therefore not entitled to an EOT unless the delay to progress will result in the contract completion date being missed. So, the Employer would say that it ‘owns’ the float.

What does the Contract say?

The issue of who ‘owns’ the float is often the cause of disputes between parties to a construction contract over entitlement to EOTs. The first port of call in the event of a dispute arising on this issue will be to review the terms of the contract. In the UK, the express issue of ‘float’ rarely appears in standard form contract conditions. However, the answer may appear in the EOT provisions. Where the EOT clause states that an EOT is only to be granted if the Employer delays completion beyond the contract completion date, then the likely effect of that wording is that the total float has to be used up before an EOT will be due (i.e. the Employer would ‘own’ the float). If, on the other hand, the EOT clause states that an EOT will be due whenever the Employer’s delay makes the Contractor’s planned completion date later than it would have been if it were not for that delay, then the total float will probably be available for the benefit of the Contractor.

However, most contracts give no indication as to whether an Employer delay has to affect the contract completion date or merely the Contractor’s planned completion date before an EOT is due. That is why parties should ensure that this issue is properly addressed at contract negotiation stage.

If the Contract is silent, does the Contractor own the float?

Prior to the 1999 case of Ascon Contracting Limited v Alfred McAlpine Construction Isle of Man ltd., if the contract was silent on the issue of float, the general approach adopted in the UK was that the Contractor would own the float because it was the Contractor who had built the float into the program to provide a cushion for unforeseen problems. However, the current approach as established in the McAlpine case and supported by the Society of Construction Law Delay and Disruption Protocol, is that an Employer delay has to be critical before an EOT will be due. This has the effect that float is not time for the exclusive use or benefit of either the Employer or the Contractor but, rather, exists for the benefit of all parties to the contract. So, even if an Employer delay causes a delay to a Contractor’s planned completion date, an EOT will not be due unless that delay resulted in a delay to the overall contract completion date.

In terms of what that means for acceleration costs, in the event that a Contractor sought to accelerate the works in order to keep the float, the current position is that, unless the contract states otherwise, such costs would not be recoverable as the float would belong to the project rather than to one of the parties.

This position can lead to unfairness and ambiguity. For instance, under contracts where Employer delay has to affect the critical path before the Contractor is entitled to an EOT; if an Employer delay occurs first and uses up all the float, then the Contractor can find itself in delay and paying LADs as a result of a subsequent Contractor delay which would not have been critical if the Employer Delay had not occurred first. However, on the other hand, under contracts where the Employer delay only has to affect the Contractor’s planned completion date, the Contractor is potentially entitled to an EOT every time the Employer delays any of the Contractor’s planned activities, irrespective of their criticality to meeting the contract completion date.

The position established in the English courts is that neither party owns the float if the contract is silent on the issue and the Contractor will only be entitled to an EOT for an Employer delay which impacts on the critical path i.e. the courts have elected not to confer a benefit on either party in the event of the parties’ failure to deal with the issue in their contracts.

Given the position taken by the Courts, it’s important to deal with the issue of float during the contract negotiation stage.


–       FLOAT is the amount of time that a task can be delayed without affecting the project’s final delivery date.

–       FLOAT is simply the subtraction of the time allotted to complete a task from the time the task actually takes.

–       FLOAT may be maximized by reassigning resources and work schedules and increasing team productivity and efficiency.

–       FLOATS have benefits such as Resource Leveling and Delay Analysis.

–       FLOAT types are:

o  Total Float

o  Free Float

o  Interfering Float

o  Independent Float

o  Safety Float

o  Remaining Float

–       FLOAT’s ownership is a cause of disputes between parties to a construction contract.

o  Contractor or Employer may argue that it ‘owns’ the float

o  What the Contract says may resolve such an argument

o  SCL Delay and Disruption Protocol supportsthat Float is not time for the exclusive use or benefit of either the Employer or the Contractor but, rather, exists for the benefit of all parties to the contract.