Float or sink

An activity has a natural duration. When the total time available for the execution of the activity is reduced by the actual duration time, the residue time is termed Float. Activities without float are said to be on the critical path.

Under the NEC, managing float is a key activity for both the surveyor and manager. The contract states that terminal float – that is, float that, if expended, will cause the project to go into delay – belongs to the contractor. It is at the employer’s risk. Float that can be used while not threatening any completion dates belongs to the project.

In programming terms, there are four types of float: total float is the maximum free time available within which the activity could take place, allowing for the time required to do the activity itself.

Total float may be subdivided into the remaining three types.

Free float is the amount of spare time that can be used without affecting subsequent activities. However, the activity must start at its earliest time.

Interfering float is the amount of spare time available, if used, which will affect subsequent activities.

Independent float is defined as the spare time available that can be used without affecting subsequent activities and that cannot be affected by preceding activities.

Only the use of free float, provided the activity starts at the earliest possible juncture, will leave the planned durations of subsequent activities unaffected.

A calculation of this nature takes on increasing importance as the number of compensation events increase and as the project enters its final trimester of activity.

Time Risk allowances

We define Time Risk allowance as the period needed to accommodate events that are not expected to arise, are at the contractor’s risk, and that, should they arise, would have a significantly detrimental effect on the activity’s planned duration.

An example would be where imported goods are given a four to nine-day period to clear customs. The risk period is five days. The (sub)contractor owns the float and the risk.

Compensation Events

A sub-contractor would be well advised to approach the main contractor with a schedule of key activities before committing to the master programme

Programmes scheduled using a computerised, logic-linked critical path analysis can provide this detail. The nuances and subtleties can be allowed for and, more importantly, modelled, in the event that corrective action is required.

However, this needs to be an ongoing activity. Short-term programmes – that is, monthly, weekly or staged programmes – must be extracted from the master programme, and staff responsible for delivering these must be aware of how short-term targets fit into the whole.

If a Compensation Event occurs – an event at the employer’s risk that allows contractors more time and money – a quotation must be produced. A quotation must take full account of the effect of the change, including the costs of disruption and prolongation.

The Compensation Event’s consequences must be determined by analysing its effect on the short- and medium-term programme.

Where activities seem to exceed their critical duration, a reassessment of the master critical path network must be made before the full and total effect of the Compensation Event can be appreciated.

All this is to be provided to a strict timetable, and the resultant quotation, if accepted, is not open to review, even if found to be in error.

The essence of the NEC is that you identify events that are likely to cause change and cost and agree them up front, and then proceed with the works. This can be a difficult task when the main contractor may be grappling with several subcontractors’ claims, all of which are affected by the same Compensation Event.

The problem is compounded when several Compensation Events occur together.

A subcontractor would be well advised to approach the main contractor with a schedule of key activities before they commit to the master programme.

Each activity should be given planned labour resources. The parties should be looking to see how the labour histogram of site personnel fluctuates, and seek to smooth it.

It is important to appreciate what this smoothing will entail, as the labour mix and activity durations may change. It may mean that the subcontractor’s anticipated programme needs reviewing. For this reason, a tender must carry with it an expectation of key activities with their durations.

Alternatively, the pre-contract enquiry programme must be fully resourced before the final price is submitted.