Walkable set pieces visible on camera — stairs, platforms, bridges where actors move. Built sturdy enough for crew and equipment.
You need a staircase in the shot that your actor actually walks up — not just pretends to. That's a practicable. Any walkable set element that is constructed sturdy enough for people and camera falls under this category: stairs, platforms, ramps, bridges, even balconies. The crucial difference from regular set dressing — a practicable must function. It must bear weight, allow for movement, let the camera track along without shaking or collapsing.
This is often underestimated in day-to-day production. The construction department builds you a nice staircase. Then the DP stands there and says, "We're going to track the camera as he walks up." Now the problem arises. The staircase shakes, the camera shakes too — the shot becomes unusable. A true practicable is constructed differently: reinforced load-bearing structure, wider steps, non-slip surfaces, handrails to hold onto. The construction costs more time and money than a simple decorative solution, but it saves you half the takes in the edit and your first assistant a nervous breakdown.
A stable practicable is particularly indispensable for Steadicam or tracking shots. If your operator is supposed to walk up the stairs with the Steadicam while the actor walks ahead — you need a construction that can bear 150 kilos of equipment plus operator plus actor and transmit no visible vibrations. In the horror or thriller genre, practicables are also important for sound design: real footsteps on real stairs sound different from sound effects that would have to be purchased later.
On set, you should clarify early with Production Design and the Steadicam team where actual practicables are necessary and where tricks will suffice — cuts, changes in perspective, or a locked-off camera. Building a walkable bridge for a single static shot is a waste of resources. But a staircase over which you shoot multiple scenes from different angles should be stable. This not only saves money in the edit but also gives your actors the confidence to act naturally — they know there is solid ground beneath them, not a wobbly makeshift solution.