Stairs

Stairs are a structure designed to bridge a large vertical distance between lower and higher levels by dividing it into smaller vertical distances. This is achieved as a diagonal series of horizontal platforms called steps which enable passage to the other level by stepping from one to another step in turn. Steps are very typically rectangular, but may instead be straight, curved, or may consist of two or more straight pieces connected at angles.
Types of stairs include staircases and escalators. Some alternatives to stairs are elevators, stairlifts, inclined moving walkways, ladders, and ramps. A stairwell is a vertical shaft or opening that contains a staircase. A flight is an inclined part of a staircase consisting of steps.

History

This is an excerpt from Staircase.
The concept of stairs is believed to be 8000 years old, and is one of the oldest structures in architectural history. The oldest example of spiral stairs dates back to the 400s BC. Medieval architecture saw experimentation with many different shapes, and the Renaissance even more so with varied designs.

Components and terms

A stair, or a stairstep, is one step in a flight of stairs. A staircase or stairway is one or more flights of stairs leading from one floor to another, and includes landings, newel posts, handrails, balustrades, and additional parts.
In buildings, stairs is a term applied to a complete flight of steps between two floors. A stair flight is a run of stairs or steps between landings. A stairwell is a compartment extending vertically through a building in which stairs are placed. A stair hall is the stairs, landings, hallways, or other portions of the public hall through which it is necessary to pass when going from the entrance floor to the other floors of a building. Box stairs are stairs built between walls, usually with no support except the wall strings.
Stairs may be in a "straight run", leading from one floor to another without a turn or change in direction. Stairs may change direction, commonly by two straight flights connected at a 90° angle landing. Stairs may also return onto themselves with 180° angle landings at each end of straight flights forming a vertical stairway commonly used in multistory and highrise buildings. Many variations of geometrical stairs may be formed of circular, elliptical and irregular constructions.
Ascending a set of stairs to a higher floor is often referred to as going "upstairs", the opposite being "downstairs". The same words can also be used to mean the upper or lower floors of a building, respectively.

Steps

Each step is composed of a tread and a riser. Some treads may include a nosing.

Tread: The part of the stairway that is stepped on. It is constructed to the same specifications as any other flooring. The tread "depth" is measured from the back of one tread to the back of the next. The "width" is measured from one side to the other.
Riser: The near-vertical element in a set of stairs, forming the space between one step and the next. It is sometimes slightly inclined from the vertical so that its top is closer than its base to the person climbing the stairs. If a physical riser is not present, the design is described as "open riser". This is often the case in unfinished basements.
Nosing: An edge part of the tread that protrudes over the riser beneath. If it is present, this means that, measured horizontally, the total "run" length of the stairs is not simply the sum of the tread lengths, as the treads overlap each other. Some building codes require stair nosings in specific cases where the tread depth is below a minimum value. They provide additional length to the tread without changing the pitch of the stairs.
Starting or feature tread: Where stairs are open on one or both sides, the first step above the lower floor or landing may be wider than the other steps and rounded. When the starting step is rounded, the balusters typically are arranged in a true spiral around the circumference of the rounded portion, and the handrail has a flat spiral called a "volute" that connects the tops of the balusters. Besides the cosmetic appeal, starting steps allow the balusters to form a wider, more stable base for the end of the handrail. Handrails that simply end at a post at the foot of the stairs can be less sturdy, even with a thick post. A double-ended feature tread can be used when both sides of the stairs are open. There are a number of different styles and uses of feature tread.
Stringer board, stringer, or sometimes just string: The structural member that supports the treads and risers in standard staircases. There are typically three stringers, one on either side and one in the center, with more added as necessary for wider spans. Side stringers are sometimes dadoed to receive risers and treads for increased support. Stringers on open-sided stairs are called "cut stringers".
Tread rise: The distance from the top of one tread to the top of the next tread.
Total rise: The distance the flight of stairs raises vertically between two finished floor levels.
Winders: Winders are steps that are narrower on one side than the other. They are used to change the direction of the stairs without landings. A series of winders form a circular or helical stairway. When three steps are used to turn a 90° corner, the middle step is called a kite winder as a kite-shaped quadrilateral.
Trim: Various moldings are used to decorate and in some instances support stairway elements. Scotia or quarter-round are typically placed beneath the nosing to support its overhang.
Curtail step: A decorative step at the bottom of a staircase that usually houses the volute and volute newel turning for a continuous handrail. The curtail tread will follow the flow of the volute.
Handrails

The balustrade is the system of railings and balusters that prevents people from falling over the edge.

Banister, railing, or handrail: The angled member for handholding, as distinguished from the vertical balusters which hold it up for stairs that are open on one side. Railings are often present on both sides of stairs, but can sometimes be only on one side or absent altogether. On wide staircases, there can be one or more railings between the two sides. The term "banister" is sometimes used to mean just the handrail, sometimes the handrail and the balusters, or sometimes just the balusters.
Volute: A handrail end element for the bullnose step that curves inward like a spiral. A volute is said to be right or left-handed depending on which side of the stairs the handrail is as one faces up the stairs.
Turnout: Instead of a complete spiral volute, a turnout deviates from the normal handrail center line away from the flight to give a wider opening as one enters the staircase, The turnout is usually set over a newel post to give added stability to the handrail.
Gooseneck: The vertical handrail that joins a sloped handrail to a higher handrail on the balcony or landing is a gooseneck.
Rosette: Where the handrail ends in the wall and a half-newel is not used, it may be trimmed by a rosette.
Easings: Wall handrails are mounted directly onto the wall with wall brackets. At the bottom of the stairs, such railings flare to a horizontal railing and this horizontal portion is called a "starting easing". At the top of the stairs, the horizontal portion of the railing is called an "over easing".
Core rail: Wood handrails often have a metal core to provide extra strength and stiffness, especially when the rail has to curve against the grain of the wood. The archaic term for the metal core is "core rail".
Baluster: A term for the vertical posts that hold up the handrail. Sometimes simply called guards or spindles. Treads often require two balusters. The second baluster is closer to the riser and is taller than the first. The extra height in the second baluster is typically in the middle between decorative elements on the baluster. That way the bottom decorative elements are aligned with the tread and the top elements are aligned with the railing angle.
Newel: A large baluster or post used to anchor the handrail. Since it is a structural element, it extends below the floor and subfloor to the bottom of the floor joists and is bolted right to the floor joist. A half-newel may be used where a railing ends in the wall. Visually, it looks like half the newel is embedded in the wall. For open landings, a newel may extend below the landing for a decorative newel drop.
Finial: A decorative cap to the top of a newel post, particularly at the end of the balustrade.
Baserail, or shoerail: For systems where the baluster does not start at the treads, they go to a baserail. This allows for identical balusters, avoiding the second baluster problem.
Fillet: A decorative filler piece on the floor between balusters on a balcony railing.

Handrails may be continuous or post-to-post. For continuous handrails on long balconies, there may be multiple newels and tandem caps to cover the newels. At corners, there are quarter-turn caps. For post-to-post systems, the newels project above the handrails.
Another, more classical, form of handrailing that is still in use is the tangent method. A variant of the cylindric method of layout, it allows for continuous climbing and twisting rails and easings. It was defined from principles set down by architect Peter Nicholson in the 18th century.

Other terms

Flight: Any uninterrupted series of steps between floors or levels.
Landing, or platform: A landing is the area of a floor near the top or bottom step of a stair. An intermediate landing is a small platform that is built as part of stairs between main floor levels and is typically used to allow the stairs to change directions, or to allow the user a rest. A half landing, or half-pace, is where a 180° change in direction is made, and a quarter landing is where a 90° change in direction is made. As intermediate landings consume floor space, they can be expensive to build. However, changing the direction of the stairs allows stairs to fit where they would not otherwise, or provides privacy to the upper level as visitors downstairs cannot simply look up the stairs to the upper level due to the change in direction. The word 'landing' is also commonly used for a general corridor in any of the floors above the ground floor of a building, even if that corridor is located well away from a staircase.
Apron: This is a wooden fascia board used to cover up trimmers and joists exposed by stairwell openings. The apron may be moulded or plain, and is intended to give the staircase a cleaner look by cloaking the side view.
Balcony: For stairs with an open concept upper floor or landing, the upper floor is functionally a balcony. For a straight flight of stairs, the balcony may be long enough to require multiple newels to support the length of railing.
Floating stairs: A flight of stairs is said to be "floating" if there is nothing underneath. The risers are typically missing as well to emphasize the open effect, and create a functional feature suspended in midair. There may be only one stringer or the stringers otherwise minimized. Where building codes allow, there may not even be handrails.
Mobile safety steps: Can be used as temporary, safe replacements for many types of stairs
Runner: Carpeting that runs down the middle of the stairs. Runners may be directly stapled or nailed to the stairs, or may be secured by a specialized bar, known as a stair rod, that holds the carpet in place where the tread meets the riser.
Spandrel: If there is not another flight of stairs immediately underneath, the triangular space underneath the stairs is called a "spandrel". It is frequently used as a closet.
Stairwell: The spatial opening, usually a vertical shaft, containing an indoor stairway; by extension, it is often used to include the stairs it contains.
Staircase tower: A tower attached to, or incorporated into, a building that contains stairs linking the various floors.