The Application of Start-to-Finish [SF] Relationship in Primavera P6

In Primavera P6, defining logical relationships between activities is an essential step for building an accurate and realistic project schedule. The Primavera P6 provides four types of activity relationships, which are Finish-to-Start (FS), Start-to-Start (SS), Finish-to-Finish (FF), and Start-to-Finish (SF). Each serves a specific purpose in sequencing project tasks.

Among these, the Start-to-Finish (SF) relationship is the least commonly used but can be used to play a vibrant role in certain scheduling scenarios, such as shift handovers, system transitions, temporary dependencies, or to decrease the float. Understanding when and how to use SF, along with the other three relationships, is essential for ensuring logical dependencies, optimizing project timelines, and maintaining an efficient workflow.

This article will explain how to use the SF relationship in decreasing the float of some activities in Primavera P6, as mentioned by the DCMA 14-Point Assessment that the total float should not be more than 5% in the schedule.

What is the Start-to-Finish [SF] Relationship

Definition

A relationship between activities in which a successor activity cannot be completed until its predecessor activity starts.

Finish-to-Start versus Start-to-Finish

In Primavera P6 and other scheduling tools, activity relationships define how tasks are logically connected. Two of these relationships are often compared due to their contrasting logic and application, which are the Finish-to-Start (FS) and Start-to-Finish (SF)—the differences between them are in the table below:

Why a Start-to-Finish relationship is not allowed

There is no official rule prohibiting the use of Start-to-Finish (SF) relationships in Primavera P6 schedules according to DCMA or any other major scheduling guideline. However, the DCMA 14-Point Assessment and best practices in project scheduling strongly discourage its use due to its counterintuitive logic and potential to complicate schedule interpretation.

The DCMA 14-Point Assessment recommends that at least 90% of activity relationships be Finish-to-Start (FS), making Start-to-Finish (SF) relationships rare but not explicitly forbidden. Other scheduling standards, such as AACE International Recommended Practices (RP 52R-06) and the PMI PMBOK Guide, also prefer FS, SS, and FF relationships over SF. You can check our article about how to review a baseline according to the DMCA and AACE standards from here, plus you can find a free checklist.

How to decrease the float by using the Start-to-Finish (SF)

In this article, I will explain how we can decrease the float to match the DCMA 14-Point Assessment with the SF relationship and then remove the relation to submit a schedule with as many logical relationships as possible.

The scenario in the screenshot below shows that the total float for activity A is critical. However, B is not critical but depends on A; it is not logical to submit the shop drawing this early when, in fact, the activity will be constructed later with a float of 21. In larger projects, this will assume that the contractor will submit all the shop drawings early in the project even if it is not necessary.

So, I will use the SF relationship to shift the shop drawings activities for the construction activity that is not critical.

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The start date of the project is 11-Feb-2025, as can be seen.

1. Here, we can change the Finish-to-Start FS relationship between Submittal B and Approval B and between Approval B and Construction B to Start-to-Finish SF.

Note: ensure that when you are on the submittal B activity, the SF relationship is in the predecessor. The same is to be applied for approval, Construction B is the predecessor of approval B with a SF relationship.

2. As can be seen in the above screenshot, the submittal and approval for activity B were shifted to the right (before the construction of the activity) with a 5-day float. So, we want the new date of the submittal for activity B to be the date after changing the type of relationship which is 12-Mar-2025

3. I will then export the relationships from Primavera P6.

4. Filter only on the activities with the Start-to-Finish SF relationships.

5. We will take a copy from the (SF Relationships only) and paste it into a different Excel sheet.

6. In our working sheet, we will delete all the SF relationships. By typing d in the “Delete This Row” column.

7. We will close and import the sheet to our schedule in Primavera P6. You will find that Submittal B and Approval B are no longer with relationships.

8. We then will open the sheet we imported and paste the deleted rows that we copied into another sheet. In this step, we deleted all the SF relationships in the schedule.

9. Now, we want to change the SF relationships we added to Excel to logical relationships.

9.1 We will place the submittal activity in the Predecessor column and the approval activity in the Successor column. We took the submittal activity from the successor and placed it in the predecessor column and the approval activity from the predecessor column to the successor column. And changed the relationship type to FS.

9.2 We will take the submittal activities place them in the successor column, place the start milestone in the Predecessor Column, and change the relationship to SS.

9.3 Then, from the old SF relationship we will take the predecessor start date and subtract it from the Project start date. The resulting number will be the lag we need to make the submittal start on this date.

9.4 Don’t forget to delete the SF relationships that we re-added to help us locate the activity on the exact date with less float. Also, remove unnecessary columns like dates and so on.

No SF relationships should be on the Excel sheet after finishing this step, and avoid leaving the dates columns after finishing to avoid importing issues.

9.5 Decrease the Lag some days to give yourself some buffer and avoid negative lag when importing. In this example, we decrease 10 days.

9.6 Add the relationship between the Approval drawing and the Construction activity that follows.

9.7 Your sheet should look like this.

9.8 Now we import the sheet.

1.5   And there you go.

Conclusion

Using the Start-to-Finish (SF) relationship to introduce lags between preconstruction activities and the start milestone can be an effective strategy for reducing total float and ensuring a more realistic project timeline. As per the DCMA 14-Point Assessment, managing total float is critical to maintaining the integrity of a project schedule. By strategically applying the SF relationship, planners can tighten activity dependencies and minimize excessive float, and by that, they can enhance the schedule and improve project control.

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