The Effects of Adjusting Schedules is an informational guide detailing schedule adjustments you can make, and how they affect your job schedules in BuildPro. This guide addresses durations, offsets, and date changes. This section deals with Predecessor based scheduling. Click here for an explanation of Stage/Rank based scheduling.
Predecessor based scheduling is different than stage/rank based scheduling in that instead of using ranks to determine what task is next in the schedule, predecessors are used. Each task in a schedule should have a predecessor (except for the first task) and each predecessor is associated with a system assigned ID. These IDs are used to tell the schedule which task follows the next. Predecessor based schedules do have a critical path, and critical path tasks are flagged accordingly.
Figure 19
When the duration is changed on a task the rest of the schedule is pushed out to take into account the new duration days. Since predecessor scheduling does not deal with critical path tasks, it does not matter which task you change the duration on, the schedule will move to reflect the change. However, keep in mind that if a task has no dependencies (no other tasks that precede or are linked to it) this task’s dates will not change because it is not dependent on another task ending before it can start. Also, if a task has already been started, its dates will not be affected as explained in stage/rank based scheduling. Basically, in predecessor based scheduling, dates will only adjust for scheduled tasks and for tasks that are dependent on other tasks.
In predecessor based scheduling the start date on a task must follow the end date of its preceding task. For example, in Figure 19 the duration for the Interior Paint task is 3 days. Notice that the end date for its preceding task (Interior Trim Labor) is 7/28/2004, so the start date of Interior Paint has to be 7/29/2004. In Figure 20 the duration days are changed from 3 days to 6 days for Interior Paint. The result is the tasks below were all pushed out by 3 days. Also, the end date for Interior Paint changed to 8/5/2004, so the start date changed for the task that follows (Interior Trim Labor) to 8/6/2004. The same happens to all other scheduled tasks throughout the schedule.
Figure 20
If there is one task that depends on two predecessors these tasks do not have the same end date, the task that follows will start following the task that has the latest end date.
Figure 21
In Figure 21 both the Interior Trim Labor I task has two predecessors; Interior Trim Material and Measure Countertops. However, these two tasks do not have the same end date. So, BuildPro takes the later start date of these two tasks to determine when the Interior Trim Labor I task starts. Notice Interior Trim Labor I starts on 5/3/2005 following the later end date of the Measure Countertops task.
Modifying the Offset field also affects schedules in BuildPro when using Predecessor based scheduling. Usually a task will directly follow its predecessor, but offsets can change this. Basically, if affects when the next task will start based on the task’s predecessor and number of offset days. Also, as with any schedule, weekends are taken into account. In Figure 22 the Offset for all tasks is 0. Changing the offset on any of these tasks will affect the start date of the tasks that follow based on its preceding task. For example, in Figure 22, the Gutters task has an offset of 0 so it directly follows its preceding task (Landscape). The start date for Gutters (7/1/2005) comes directly after Landscape’s end date (6/30/2005) with no days in between.
Figure 22
If the Offset is changed on the Gutters task, this will change its start date. Notice in Figure 23 that the Offset of the Gutters task has been changed to 2. The start date of Gutters is now 7/5/2005 which takes into account the offset of 2 days plus a weekend. Also, the start date for the Final Grade task gets pushed out 2 days because its predecessor is Gutters. Offsets can also be negative numbers. See Figure 24 for an example of how a negative offset affects a schedule.
Figure 23
Notice in Figure 24 that the Offset for Landscape is now set to negative 2. The start date is now 2 days earlier (moved from 6/30/2005 to 6/28/2005). Now, Landscape’s start date is one day before its preceding task (Flatwork). According to Flatwork, Landscape should start on 6/30/2005 b/c Flatwork doesn’t end until 6/29/2005, but since the offset for Landscape is a negative 2, it needs to start 2 days before making the start date 6/28/2005.
Figure 24
Go to Stage/Rank Scheduling