A Time Impact Analysis is a method used to determine extent of impact from potential delay in construction process. This schedule analysis method involves the insertion or addition of activities indicating delays or changes into an updated schedule representing progress up to the point when a delay event occurred to determine the impact of those delay activities.
Types of Delays
Delays can be categorized in two main areas:
- Excusable Delays
Excusable Delays occurs due to events which are outside the control of contractor like heavy rains, storms, strikes, fire, client suggested changes, differing site conditions, change of government policy… etc.
When there are excusable delays, contractor is entitled to time extension in case date of completion is extended. Such delays can also affect non critical activities which must be considered with more detailed analysis.
Excusable delays can be further classified in compensable and noncompensable delays.
- Excusable Compensable Delays
As name suggests excusable compensable delays are those in which contractor is entitled for extra payment (compensation) i.e. monetary compensation and time extension as well. But decision that a delay is compensable or noncompensable is taken as per contract between client and contractor. Natural disasters or some reasons which are out of control are not considered. Example of such delay could be that client doesn’t allow access to site even after notice to proceed is given; other such delays which are due to client are compensable.
- Excusable Noncompensable Delays
Such delays are such where both contractor and client are not responsible for delay. Under such circumstances only time extensions are granted and no monetary compensation is provided. Such delays include act of God.
2. Non-Excusable Delays
As name suggests these delays are such that they don’t have any excuse or no excuse can be given for them. They arise due to carelessness or actions and inactions of contractors and subcontractors. For such delays no time extensions and monetary compensation is given to contractor if it has affected whole duration of project. In such cases client is liable to get liquidated damages. Example of such delay could be constructing something wrong which is not given in drawings, not completing work on time, improper resource allocation etc.
We have a simple project with the Planned schedule like this:
We have delay (21 days) on Excavation due to Unforseen site condition
We have no delay.
We have 2 delays:
- Owner change house design (14 days)
- Subcontractor left job (21 days)
And those are concurrent delay. So 14 days charge to owner, and 7 day charge to contractor
We have 1 delay from Contractor in “Garage Walls” but it was not on the critical path. As long as the delay is within available float there is no effect on the final completion date.
We have 1 delay (28 days) from Owner in Garage Doors but it only affect 7 days in the critical path. Other 21 days were absorbed by available float.
We don’t have any delay.
So we can have the Time Impact Analysis report like this:
- 28 days for time and cost
- 14 days for time
Differences between Window Analysis and Time Impact Analysis:
This technique involves interim assessment of delay on updated schedules at specific periods of the project. This is similar to the “snapshot technique” and “contemporaneous
period analysis”. First, the total project duration is divided into a number time periods (windows or snapshots) usually based on major changes in planning or major project milestones. The schedule within each window is updated to reflect the actual duration and sequence at the time of the delay while the remaining as-planned schedule beyond the window period is maintained. Analyses are performed to determine the critical path and new completion date. This new completion date is compared with the as-planned completion date prior to this analysis to give the amount of delay during that window period.
Time Impact Analysis:
This technique is a variant of the window technique described above, with the difference being that the time impact technique concentrates on a specific delay or delaying event but not on time periods containing delays or delaying events.
A stop-action picture of the project is developed each time it experiences a major delay situation. The schedule is then updated at this delay period and the effect of the delay is analysed to establish a new completion date. The difference between the new completion date and the date prior to the exercise gives the delay caused by that particular impact.
However its limitations include: it may not be practical or realistic to use if there are an overwhelming number of delay causing events.