Stairs that are solid underneath

[Anonymous]

I am trying to figure a way to model a stair that is completely solid underneath. All of the options seem to be with space underneath the stair. In the attached picture, I've shown the area that I would like filled in. Thanks!

[Barry Kelly]

You won't get the stair objects to do that.
I think your best option will be to add a slab underneath and then use the stair as a Solid Element Operator and 'subtract with upward extrusion' to remove the top of the slab.
Barry.