Primavera P6 Relationship Types: Project Scheduling
- Michelle M
- Jun 20
- 5 min read
Primavera P6 is one of the most powerful and widely used scheduling tools in project management today. From construction to complex IT deployments and infrastructure projects, Primavera P6 gives planners, schedulers, and project managers the power to plan with precision, forecast effectively, and provide timely delivery
Primavera P6’s scheduling manages activity relationships with logical sequencing of tasks and activities in a project. These relationships dictate how tasks are linked, in what order they must be performed, and the nature of the dependency between them. Without correctly defining relationships in Primavera P6, even the most detailed Work Breakdown Structure (WBS) can fall apart, leading to unrealistic schedules, missed deadlines, and costly rework.
This blog explores the four key relationship types in Primavera P6, how they function, when to use them, and why understanding them is critical for creating a meaningful, dynamic project schedule.
What Are Activity Relationships in Primavera P6?
Activity relationships in Primavera P6 define the sequence and logical dependency between project tasks. They are used to create a network diagram, or Critical Path Method (CPM) schedule, where each activity is connected to others through predecessors and successors.
These relationships influence:
The start and finish dates of activities
The critical path of the project
The total float or slack of activities
How delays propagate through the schedule
There are four primary relationship types in Primavera P6:
Finish-to-Start (FS)
Start-to-Start (SS)
Finish-to-Finish (FF)
Start-to-Finish (SF)
Each of these relationships can be enhanced with lags or leads (negative lags), giving project managers the ability to model real-world dependencies with high fidelity.
Let’s look at each of these in detail.
1. Finish-to-Start (FS)
Definition:
The most commonly used relationship type. In a Finish-to-Start (FS) relationship, the successor activity cannot start until the predecessor has finished.
Example:
Task A: Pour concrete foundation
Task B: Build walls
Task B can’t start until Task A is complete. Therefore, Task A →FS→ Task B.
Use Case:
Finish-to-Start is used in scenarios where one activity's output is a direct prerequisite for the next. In construction, manufacturing, and software development, FS relationships help enforce sequential logic.
2. Start-to-Start (SS)
Definition:
In a Start-to-Start (SS) relationship, the successor activity can start only after the predecessor has started. Both activities can proceed simultaneously after the predecessor starts.
Example:
Task A: Start writing code
Task B: Begin testing modules (as coding starts)
Testing can begin as coding begins but does not wait until coding is finished.
Use Case:
SS relationships are used when parallel tasks can be initiated together but may end independently. It’s common in Agile development, overlapping construction trades, or events planning.
3. Finish-to-Finish (FF)
Definition:
In a Finish-to-Finish (FF) relationship, the successor activity cannot finish until the predecessor finishes. They may start at different times but must conclude together.
Example:
Task A: Finalize design
Task B: Complete documentation
Documentation may begin earlier but can’t finish until the design is finalized.
Use Case:
FF relationships help ensure that dependent activities wrap up at the same time. Common in quality assurance, editorial workflows, or technical writing processes tied to design.
4. Start-to-Finish (SF)
Definition:
In a Start-to-Finish (SF) relationship, the successor cannot finish until the predecessor starts. This is the rarest and least intuitive relationship.
Example:
Task A: Begin shift for security team B
Task B: End shift for security team A
Team B must start before Team A finishes their shift. This ensures continuous coverage.
Use Case:
SF is used in scenarios involving handoffs, shift changes, or tasks that depend on another starting before one can end. It's uncommon but useful in operations-heavy environments.
Enhancing Relationships: Lag and Lead Time
Primavera P6 allows users to modify activity relationships by adding:
Lag: A delay between the predecessor and successor.
Lead (Negative Lag): An overlap that allows the successor to start before the predecessor finishes.
Example of Lag:
Task A: Paint walls
Task B: Install carpet
Add a 2-day lag between the finish of painting and the start of carpet installation to allow drying time.
Example of Lead:
Task A: Write user guide
Task B: Review user guide
Add a -3 day lead, allowing reviewers to start while documentation is still being written.
Understanding how to use lag and lead correctly can optimize scheduling realism and prevent unnecessary idle time.
Applying Relationship Types in Primavera P6
How to Assign Relationships:
Open your project schedule.
Click on the activity you want to link.
Go to the “Relationships” tab.
Add Predecessors or Successors.
Choose the relationship type from the dropdown (FS, SS, FF, SF).
Add lag/lead if necessary.
You can also define relationships using network diagram view or activity table with drag-and-drop functionality.
Best Practices for Using Relationships in Primavera P6
1. Stick to FS as Default
FS is the safest and most understood relationship. Use it for clarity and when in doubt.
2. Minimize SS and FF Overuse
SS and FF are powerful but can create complex networks. Use them only when truly needed to model real-world overlaps.
3. Be Cautious with SF
Since it’s rarely used, SF relationships can confuse teams and should be clearly documented.
4. Document Lag and Lead Logic
Always explain why a lag or lead is used, especially in shared schedules. Misunderstood lags can create timing errors and critical path distortions.
5. Avoid Redundant or Circular Logic
Too many relationships between the same pair of activities (e.g., FS and FF) can create redundancy and increase the risk of errors.
6. Recalculate the Schedule After Updates
Use F9 or go to Tools > Schedule to recalculate the timeline after making changes.
The Role of Relationships in Critical Path Analysis
Activity relationships play a central role in determining the critical path the longest duration path through the project that determines the shortest possible completion time.
Incorrect or poorly assigned relationships can:
Mask delays
Create artificial float
Cause the schedule to be overly optimistic or pessimistic
For accurate risk analysis, baseline tracking, and project forecasting, relationships must be carefully reviewed and regularly updated.
Relationship Types and Resource Management
Primavera P6 doesn’t just schedule tasks it also allocates labor, materials, and costs. Relationships impact:
When resources are needed
How resource conflicts are resolved
Whether overtime or reallocation is required
By aligning logical relationships with resource availability, schedulers can optimize workforce planning and reduce bottlenecks.
Common Mistakes in Setting Relationships
Only using FS and ignoring opportunities to optimize timelines with SS or FF.
Using excessive lag/lead instead of breaking tasks into smaller subtasks.
Neglecting to update relationships after scope or sequence changes.
Creating “dangling” activities with no predecessors or successors, breaking logic.
Failing to run schedule diagnostics to validate relationship integrity.
Primavera P6 Tips for Better Relationship Management
Use layout filters to identify activities with no successors or predecessors.
Leverage schedule logs to identify circular logic or constraints.
Assign activity codes to group related tasks for better logic modeling.
Document relationships and lags in a relationship matrix or notes field.
Conduct what-if analysis to test changes in logic without impacting the live schedule.
Final Thoughts: Why Relationships Matter in Primavera P6
Activity relationships are not just lines on a Gantt chart they’re the logic engine driving your entire project schedule. Getting them right means:
Achieving better time estimates
Responding proactively to delays
Aligning teams and resources with reality
Delivering projects on time and on budget
In Primavera P6, mastering relationship types FS, SS, FF, SF and knowing when and how to apply them is a critical skill for every project scheduler or manager.
The power of P6 lies not just in its features, but in how intelligently you use them. Solid, well-defined activity relationships ensure that your project plan is not just a document but a dynamic, trustworthy roadmap to success.
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