2, The materials most commonly used in the construction of stairways are stone, iron, and wood; the selection of material should be based on the location and the use to be made of the stairway. If placed outside of a building, stone, owing to its natural capability of resisting atmospheric influences, should be used; while, if placed inside a building designed to be fireproof, iron is generally selected, as it possesses great resistance to heat. Both iron and stone are preferable to wood when used in public buildings, where the amount of travel requires extra strength; wood, however, is the material most commonly used, especially in private buildings, where no heavy travel is to be expected.