A shared venue needs someone to open it every morning. If responsibility belongs to “everyone,” it can fall repeatedly to the same conscientious person. A duty roster assigns particular periods to particular people, making both coverage and gaps visible.
A rota needs more than names: shift length, backup, and workload, together with the handover between people, affect whether coverage is sustainable.
The venue could publish a monthly opening rota with a backup contact and a clear way to swap shifts. Volunteers would know when they are responsible and when they are free to stop watching for problems.
Equal numbers of shifts are not always equal burdens. Weekend mornings, interrupted nights, and quiet afternoons can impose very different costs, and people have different constraints. Training matters too: rotating an unprepared person into a role does not create competent coverage. A useful roster makes responsibility bounded and transferable, while the group continues to examine whether the work itself has become too demanding for the available people.