Staircases are assembled in 3 basic styles:
1/2 log treads with 1/2 log stringers on sides:
This version may the most economical, but may be difficult to install, notches in stringers that recieve treads require the staircase to be fully assembled, and then positioned with a heavy duty lifting device. This is easily done on new construction before a structure is closed in, but may be difficult in completed structures. Variations of the style to ease install are avalable.
1/2 log tread with full-round stringers:
This version showcases the full tread with the support stringer notched underneath to recieve treads, this option may be easier to install, once stringers have been set, treads fit in notchs and get fastened from underside.
Perhaps the most striking of log staircases, require onsite fabrication in most cases as railing is a structural part of the unit. Certain building codes must be considered with a spiral staircase.