How do I model and configure a stairwell zone that is open to the corridors in OpenStudio?

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I don’t know how to represent a free-standing staircase that connects 5 floors in the SketchUp plugin, nor how to configure such stairs in OpenStudio. Currently, I am representing the staircase as an isolated tower, and the space type I’ve assigned to it results in thick walls—but that’s not what I want. It would be much better if there were a way to use "air walls" instead.