In recent revisions of the Structural Design Codes in New Zealand, a number of changes have been made to seismic design provisions. One of the more significant revisions was the way in which the level of detailing is determined for potential plastic hinges. Previously the level of detailing was based principally on the structural ductility factor, which is broadly similar to the reduction factor, R, used in US practice. With the revision it is based on the predicted magnitude of curvature that the plastic hinge is required to sustain in the ultimate limit state. This paper explains why the structural ductility factor does not give a reliable guide to the deformation sustained in an individual plastic hinge. In addition, based on test results of 37 beams, 25 columns and 36 walls, design curvature limits are proposed for different categories of plastic hinge.