I use cement board.

There are stairs right across from it.

And no, it's unlikely that you need a custom spec mixture, but a footing mixture is typically less expensive than a slab mixture (in part due to the amount of cement in the mix as well as additives such as fiber commonly used for slabs).  

It also depends on what your doing - if stairs and hallways are not code compliant you do not have to bring those to code unless you start taking walls down etc. you typically only need to bring up to code those things that you are updating / modifying

My down stairs drain's are slow and gurgle up stairs is fine anyone have an idea what is wrong?

@Nick Horob Adding a half bath under stairs is always a good idea.  

Under stairs and reduce storage room under stairs.

And the year that made 5 years in undergrad worthwhile was living 10months in Florence, Italy (cementing my addiction to travel.)

Hire a high school kid to do the dirty work if you're committed.Otherwise just go over top with self leveling cement and then tile or whatever fake flooring you had planned (all I know is hardwood and tile).

I went up the stairs that my upstairs tenant uses to get to her door because the open window was at the top but not in her apt.