hello, I am remodeling a dangerous 1937 staircase to second story. The stair opening in ceiling is probably just too small but my question is at what point is the measure for 80" (6'8") taken in regards to the stringer side? in relation to the next tread? One place I was looking used a straight edge laid down on the stair and they measured from the diagonal line it created but this quickly reduces headroom clearance unless the very edge of the tread were below the ceiling corner you measure from!! I am not looking to have to increase the stair opening if possible while increasing the tread to 10.25 and the rise to 7.75 currently it was 9.5 run and 8.5 rise with carpet and people occassionally slip off the corner and fall down stairway becase run is not deep enough.