Not to be too much of a pain in the neck, but in my opinion the spiral staircase that alex provided us with will not work. I faced it a number of times in my own projects. Got to solve it real quick. Point is that there is no height for anyone to climb all the way up going under the loft/mezzanine floor. My suggestion for the case is to rotate the staircase by 90 degrees, and make the highest tread a square or a platform-like tread that can allow a 7 feet minimum height under the loft.