During renovating my basement, I am trying to change my u-shape stair to L-shape. Since the current two flights are located between two structural beams on the basement ceiling, I have to use winder tread to shorten the second flight so that it can go underneath the beam with enough headroom(6'8").

After checking on the web about the stair code, it seems all winder tread can't be narrower than 6", even in the inner corner. For 3-winder L-shape, it makes the use of winder pointless. People uses winders to fit stair in smaller stair well. But if the inner side of tread maintains larger than 6" then the stair will use a larger well than not using winders. Am I correct? Can someone advise me on how to fit a stair in a smaller well? Thanks.

David