Stairs of the Afkrea' Form, consisting partly of steps with parallel edges and partly of winding- steps, although occupying relatively the least space, are inconvenient on account of their irregularity, which, together with their want of beauty, renders them inapplicable to the uses of a grand stair way; such stairs, therefore, are not to be recommended. It is not neces sary to treat of back stairs among stone constructions, as they are seldom made of stone, but mostly of wood or iron.
The Perron, or outside stairway, is used only where the ascent is to be made froni the street or courtyard to the story of a building lying at a higher level. In public buildings and handsome private residences more ornamental forms of entrance are required, and in other cases simpler forms are selected. The perron in Figure 2r (pi. r) was erected as a portion of the alterations and enlarg-enient of the Hotel de \'ille in Paris, in the Cour d'Honneur, under the direction of Haussmann, prefect of the Seine. It is in the form of a horseshoe of cut stone. In simpler structures and private rcsideuces short flights of outer stairs are usually styled " steps." When used for areas or back courts, they are often made of 2- or 2Y-itich stone for the tread, the riser being formed of 4Y2- or 5-inch stone, both tailed into a wall at one or both ends. This is much lig-liter in effect, and slate is frequentiv snbstituted for stone in the tread.
Playbrms or Landings of stone are frequently placed over an area before a door, at the head of a flight of stairs, or as the floor of a balcony; they are made from 4 to S inches in thickness, according- to their extent and bearing-. When not constructed of an entire slab of stone, they are made
of jointed pieces jog-gled and phig,g-ed together, and are worked on the face and edges as the situation may demand, and should also be very carefully pinned to the walls.
The Geometrical Stoirs in stone mentioned above were not represented upon the Plate because, first, they are less to be depended upon, and con sequently are infrequently used, and secondly because their general arrange ment is simple, although they are difficult of construction. They are most advantageously nsed in the form of winding stairs, principally because in this arrang-ement the steps have the greatest bearing upon one another.
Brick the proper kind of stone is not to be had, brick stairs may be built in three ways: (r) By imitating- the form of the stone steps. Wooden box moulds are used for this purpose, the bricks being set in strong bond with cement-mortar and allowed to stand until the whole has become solid and capable of bearing- transportation. (2) By construct ing them, in the place where they are to remain, upon a support (boarding) raised a little toward the middle, which is afterward to be taken away; this method of bonding is shown in Figure 22. Cement must here be -used as mortar. (3) By building them upon a rising- vault, as seen in Figure 23. As by this construction the steps are hollow, the weight is consider ably decreased. The steps mentioned in (I) and (2) must be saddled; otherwise, all brick stairs should receive a coating- of cement, a casing- of wood, or a covering of thin marble slabs.