Start with components, not one hidden number.
Separate slab self-weight, finishes and services, partitions, and imposed load. This keeps changes visible when the architectural build-up or occupancy changes.
Tributary width is a load-path decision.
Multiplying the service area load by a one-way tributary width gives a line load in kN/m. It is a useful framing step for a beam check, not proof that the slab distributes load one-way in every location.
What still needs judgement
- Code combinations, partial factors, ψ factors, and accidental actions.
- Two-way slab behaviour, openings, walls, concentrated actions, edges, and cantilevers.
- The project basis for live load, partitions, finishes, and structural density.