The number of steps to be introduced is ascertained in the same way as for a straight stair. Thus, in the Fig. 201, a height of 10 feet 10 inches has to be gained, there are 20 risers each 6½ inches high, and the steps have a proportional breadth of 10 inches. The stair is in two flights, each containing 10 steps, and separated by a half-space landing.
The length of staircase required for the width of treads is 9x10 inches = 7 feet 6 inches; and for the landing (equal to width of stairs) 3 feet 6 inches, or 11 feet altogether.
When, however, the area of the staircase is more limited in proportion to the height to be gained, the landing must be made smaller or done away with, and winders introduced ; the steps also may be made steeper, so that fewer of them are required, and they take up less room, as the proportionate tread for each is less.
Suppose, for example, that the staircase has a length of only 8 feet, and that the height to be gained between two floors is rather more than before, viz. 11 feet 1 inch (see Fig. 204).
In this case the landing shown in Fig. 200 has to be sacrificed and winders introduced, while the steps are made steeper, so that 19 only are required; the height of each of these is 133/19 inches 7 7 inches,1 the corresponding tread being 9 inches, the total length taken up by the steps being 6 X 9 inches = 4 feet 6 inches for the fliers - in addition to 3 feet 6 inches (the space containing winders) - altogether 8 feet.