Figure 19(c) Extension at Bottom of Run. Illustrates a horizontal extension at the bottom of a stair. A 12 inch (305 mm) horizontal extension is shown plus the width of one tread. In the drawing this distance is indicated by the dimension Y. The tread width is measured from the front of the nosing to the front of the next nosing of the tread above, measured horizontally. The end of the handrail extension is returned down towards the floor and then to the support post in the same detail as in 19(d) below.