Starttostart

Start-to-Start (SS) is a type of logical relationship in project scheduling in which the start of one task (the successor) depends on the start of another task (the predecessor). In an SS link, the earliest possible start of the successor cannot occur before the predecessor has started. The relation may include a lag or, less commonly, a lead time, which shifts the timing relative to the predecessor’s start. SS is one of the traditional dependency types used in CPM and PERT, alongside Finish-to-Start, Finish-to-Finish, and Start-to-Finish.

In practice, SS is used to coordinate tasks that should begin together or when the start of one task signals the readiness to begin another. It contrasts with Finish-to-Start, where the predecessor must finish before the successor starts, and with Finish-to-Finish and Start-to-Finish, which model other sequencing constraints. A lag specifies a delay after the predecessor starts before the successor may start; an allowable negative lag (lead) can permit an earlier start than the predecessor’s start in tightly coupled activities.

Example: Task A represents site preparation and Task B represents foundation work that should begin around the time A starts. An SS link with a small lag can be used so that B starts shortly after A starts. Negative lag might be employed if B must begin before A starts due to resource or workflow considerations.

Usage and implications: SS helps model parallel or coordinated starts but can complicate schedule calculations and critical-path analysis if overused. In project management software, SS is represented as a dependency from A’s start to B’s start with an optional lag.