84. A hard stone, such as granite or bluestone, should be used for steps; but for private residences, where the wear is not great, limestone or a fairly hard sandstone may be used. Outside steps should be firmly supported at each end, and if more than 6 feet long, should also have a center bearing. Each step should overlap the one below at least 1 1/2 inches, and should have an outward pitch of about 1/8 inch. Steps having a nosing, as shown at a, Fig. 46, make a good appearance, but are much more expensive than the ordinary ones.

Stone Steps 173

Fig. 46.

85. Stone stairs are sometimes made with but one end supported. This end is built solidly into the wall, and each step is carried on the next lower one. This construction is shown in Fig. 47, in which a represents the landing rabbeted into the tread of the top step; while b shows the manner in which each step is cut and supported by the lower. To be safe, the bearing dimensions should not be less than here shown. The bottom step should be firmly held in place by dowels set into the floor (as shown at c), as this step must sustain the thrust of the whole flight of stairs. The stone blocks forming the steps are usually cut in the triangular cross-section shown, which method of cutting gives a good appearance to the soffit, or ramp, of the stairs.

Stone Steps 174

Fig. 47.

86. Iron staircases are very extensively used in fireproof construction; the treads, and sometimes the risers, are usually marble slabs. Slate, being cheaper, is also considerably used. Staircase railings, for stairways having stone or iron steps, are often elaborately finished, and are generally made of iron, doweled into the ends of the steps.