The document files opened with a Rhino template have a stair “standard” style that already has a slab by default. The VisualARQ templates include a few stair styles with slabs.
To add a slab to a specific stair style (if it doesn’t have any), open the Stair Styles dialog box _vaStairStyles. Right-click on the stair style name and the context menu will be diplayed: select New > Stair Slab.
The slab thickness can be edited from the geometry tab, when selecting the slab component.