Staircase
Also called: stairs, stair, stairbuilding, geometrical stairs, dog-leg stair, open string stair
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A staircase is a built structure of steps that carries people from one floor of a building to the next. Stairs are named two separate ways at once: by the shape they make in plan, such as dog-legged, and by how their strings, the sloping boards that carry the ends of the steps, are treated.
Naming a stair
Names describing a stair's plan shape are kept apart from names describing how its strings are built. A close, or housed, string has the step ends let into grooves cut in its face; an open, or cut, string is instead cut away to follow the profile of the steps, and is sometimes further supported by brackets, giving a bracketed string. An open-newel stair is one whose string is cut or notched rather than closed. Where a stair sits within square walls, its corners can be cut off with octagonal strings instead of a curved, circular wall string, and building it that way is sometimes cheaper. At the turn of a grand staircase, a large, elaborately carved newel, the upright post that the string, rail and steps join into, can carry the handrail framed directly into it. Away from formal usage, a free-standing circular stair is sometimes called a 'hollow newel', to tell it apart from a solid circular newel stair, though this is not a technical term.
The dog-leg stair
The dog-leg stair has no well-hole, the open gap in the middle of an ordinary stair that lets you see between the flights above and below. Without a well-hole, the handrail and balusters, the uprights that support the rail, of both flights fall in the same vertical plane, directly above one another. Its steps are fixed to the strings, the newels, and the carriages, the timbers set below the steps that support them; in common, plain-grade work the step ends simply meet the face of the string with no housing cut for them. This form suits a somewhat better-class house that has just enough width for its flights to double back on themselves, though it needs about twice the width of a straight flight to do so. The name 'dog-legged' is used almost only for wooden stairs: as Rivington (1887) put it, 'there is no distinct name for stone stairs of similar form.' A turn can also be worked into a dog-leg, or an open-newel, stair using tapered winder steps instead of a landing.
Other forms, and fitting the space
Stair forms vary a good deal in cost and the floor space they need. One kind is the costliest to build, and so is rarely made new outside bespoke, high-quality work. Another takes up less floor space than any type except a spiral stair, which is why it is chiefly used in cottages and small houses. A third is convenient but works only where there is a long run of floor available compared with the height to be climbed, and a further kind uses close strings on both sides. Winders, the tapering treads that turn a stair's corner, are sized against the straight-run treads either side of them, called fliers. On a narrow stair the winder's tread should be made as wide as a flier's, measured at the winder's mid-length; on a wide stair, the same match is instead taken about eighteen inches in from the handrail. A landing is made the same width as the stair it serves. Where there is room in the space available for the number of treads needed at a chosen width, plus the landings, that width is kept; where there is not, a steeper rise is used instead, with narrower, more numerous treads, to fit what space there is.
Framing and building
The angle a stair climbs at is called its pitch, its angle of inclination from the horizontal. In one American system of post-and-beam building, the stringer and handrail at each end of a flight join into a newel post by mortise joints, sockets cut to take a matching tenon, and that post is in turn joined by mortise into the header, the beam carrying the opening in the floor above. Building a stair belongs, strictly, to millwork rather than carpentry, but a carpenter is often the one who ends up building porches, basement stairs and attic stairs, and occasionally straightforward main flights too. To follow stair-building instructions correctly, a carpenter needs to know the standard names for a stair's parts.
Origins
Stairs are said to have evolved from portable ledged ramps that once followed cliff-side steps: early ramps were built of rammed earth, and later of stone slabs, letting people reach height before true steps existed.