Start-to-Start (SS) Relationship in Primavera P6.

Introduction

The Start-to-Start (SS) relationship is one of the four types of activity relationships in Primavera P6, used to define how two activities are dependent on each other. In a Start-to-Start relationship, the successor activity cannot start until the predecessor activity has started. However, both activities can continue simultaneously once they have begun.

This relationship is used in scenarios where two tasks can overlap, allowing for parallel execution, which can help in shortening the overall project duration.

Key Characteristics of Start-to-Start (SS) Relationship

Simultaneous Execution:

Both the predecessor and successor activities can run concurrently, but the successor can only start after the predecessor has started.

Partial Dependency:

Unlike the Finish-to-Start (FS) relationship, the SS relationship doesn’t require the predecessor activity to be completed for the successor activity to begin.

Flexibility in Scheduling:

This relationship is useful when activities need to run in parallel, providing more scheduling flexibility.

Adjustable Overlap:

Lags or leads can be applied to control the overlap between the activities.

Real-Life Examples of SS Relationship

Example 1: Construction Project

Predecessor Activity: Start excavation of the site.
Successor Activity: Start pouring the foundation.

Once the excavation starts, you can begin pouring the foundation on the parts of the site where excavation has been completed. Both activities happen simultaneously, but the successor (pouring the foundation) cannot start until the predecessor (excavation) has started.

Example 2: Software Development Project

Predecessor Activity: Start writing the user interface (UI) code.
Successor Activity: Start writing the backend code.

In this example, once the UI team begins working on the front-end design, the backend team can also start coding as long as they have the necessary information to begin. Both coding tasks can be done concurrently.

Example 3: Manufacturing Process

Predecessor Activity: Start assembling the product components.
Successor Activity: Start inspecting the assembled parts.

As soon as the assembly process begins, quality inspectors can start inspecting the components already assembled. This allows for faster progression since both tasks are happening at the same time.

Using SS Relationship in Primavera P6

To create a Start-to-Start relationship in Primavera P6, follow these steps:

Define the Activities: Ensure that you have both the predecessor and successor activities defined in your project.
Assign SS Relationship: In the Activity Details window, go to the Relationships tab, and for the successor activity, set the relationship to Start-to-Start (SS), linking it to the predecessor.
Use Lag or Lead (Optional): You can introduce lag (delay) or lead (negative lag) to control how much overlap exists between the two activities.

Lag and Lead in SS Relationship

Lag: Lag introduces a delay between the start of the predecessor and the start of the successor. For example, if there’s a 3-day lag, the successor activity will only start 3 days after the predecessor activity starts. Example: If you start painting the walls (predecessor), there might be a 2-day lag before you start painting the ceilings (successor) to allow sufficient drying time for the walls.
Lead: A lead (or negative lag) allows the successor activity to start earlier than the predecessor. For example, the successor activity might start when the predecessor is partially complete. Example: In the case of road construction, paving (successor) can start when grading (predecessor) is 50% complete.

Advantages of SS Relationship

Shortens Project Duration: Since the SS relationship allows activities to be performed in parallel, it can significantly reduce the total project duration.
Improves Resource Utilization: Teams can work on different tasks simultaneously, improving resource efficiency and avoiding idle time.
Better for Complex Projects: In large, multi-phase projects, where many activities can overlap, SS relationships offer the flexibility needed to handle complex scheduling requirements.

Limitations of SS Relationship

Difficult to Manage: Coordinating parallel activities can be challenging, especially when both activities are critical to project success.
Risk of Rework: If one activity starts too soon and relies on incomplete information from the predecessor, there’s a risk that work might need to be redone later.
Potential Delays: If the predecessor activity experiences delays, it can also delay the start of the successor activity, leading to cascading project delays.

Real-Life Scenario of SS Relationship

Example: Road Construction

Let’s consider a highway construction project where the project involves several activities that can be performed simultaneously:

Predecessor Activity: Start grading the road surface.
Successor Activity: Start paving the road.

Once grading starts in one section of the road, paving can begin on the sections that have been graded. The grading and paving activities are running concurrently in different sections of the project site. This SS relationship allows for more efficient use of time and resources, preventing unnecessary delays.

When to Use SS Relationship

Parallel Activities: When two tasks can be done simultaneously but are still logically dependent on one another, such as in construction or manufacturing processes.
Overlapping Work: When one task can begin while another is partially complete, for example, in software development, where different teams work on front-end and back-end components simultaneously.
Complex, Multi-Phase Projects: SS relationships are ideal for projects with many interdependent tasks where overlapping work can help speed up the overall project schedule.

Conclusion

The Start-to-Start (SS) relationship in Primavera P6 provides flexibility in scheduling by allowing parallel execution of activities. By linking the start of one task to the start of another, project managers can optimize time and resources, leading to faster project completion. However, it requires careful management to avoid delays or rework. Proper use of lag or lead, along with a clear understanding of task dependencies, is key to successful implementation of SS relationships in complex projects.