Schedule Buffer is a block of time added to a project activity schedule to protect due dates of scheduled tasks and jobs from delays and overlays. Buffers signify safety margins that help manage the impact of uncertainty and variation to a deliverable placed on a schedule. The term is usually used in Critical Chain Project Management (CCPM) methodology.
Defining and setting schedule buffers (buffering) means placing necessary strategic points on a schedule of project activities to ensure success of critical chain tasks. Buffering allows a project team to reach sufficient safety levels and protect project tasks from out-of-schedule durations. Buffering provides a mechanism to push resource-dependent tasks to their successful completion in the shortest possible time period.
The CCPM methodology defines four types of schedule buffers, such as:
- Project Buffer. It is placed on a project schedule between the final scheduled task of the critical chain and the estimated project end-date.
- Feeding Buffer. It is a portion of time when non-critical tasks merge with critical chain tasks. The feeding buffer protects a project from missed completion dates of non-critical chain tasks.
- Resource Buffer. It signifies an amount of working hours required by human resources to complete their critical chain tasks.
- Capacity Buffer. It is used in multi-project environments and project portfolios to plan for on-call resources and cover costs required by the resources to complete two or more projects.