The four types
- Finish-to-start: B starts when A finishes. The most common: you do not paint until the plaster is dry.
- Start-to-start: B starts when A starts. Site layout and safety signage begin together.
- Finish-to-finish: B finishes when A finishes. The installation documents are closed out with the final tests.
- Start-to-finish: B cannot finish until A starts. The rarest: the old equipment keeps running until the new one starts up.
Each one can have a lag, such as waiting two days after pouring concrete, or a lead, such as starting to paint when the plaster is half done.
The critical path
Chaining dependencies together reveals the critical path: the sequence of tasks where every day of delay is a day of delay on the handover. Tasks outside it have slack. Knowing which is which tells you where to put people when something goes wrong.
The usual mistake
Keeping dependencies in the project manager’s head. If they are not written into the plan, moving one date does not move the ones that depend on it. And the Gantt chart shows a schedule that is no longer possible.