A stairway, staircase, stairwell, flight of stairs, or simply stairs is a construction designed to bridge a large vertical distance by dividing it into smaller vertical distances, called steps. Stairs may be straight, round, or may consist of two or more straight pieces connected at angles.
Components and terminology
- Step – The step is composed of the tread and riser.
- Tread –
- The part of the stairway that is stepped on. It is constructed to the same specifications (thickness) as any other flooring. The tread “depth” is measured from the outer edge of the step to the vertical “riser” between steps. The “width” is measured from one side to the other.
- Riser – The vertical portion between each tread on the stair. This may be missing for an “open” stair effect.
- 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 actually overlap each other slightly.
- Starting step or Bullnose – Where stairs are open on one or both sides, the first step above the lower floor may be wider than the other steps and rounded. The balusters typically form a semicircle around the circumference of the rounded portion and the handrail has a horizontal spiral called a “volute” that supports the top 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 bullnosecan be used when both sides of the stairs are open.
- Stringer, Stringer board or sometimes just String – The structural member that supports the treads and risers. There are typically two stringers, one on either side of the stairs; though the treads may be supported many other ways. The stringers are sometimes notched so that the risers and treads fit into them. Stringers on open-sided stairs are often open themselves so that the treads are visible from the side. Such stringers are called “cut” stringers. Stringers on a closed side of the stairs are closed, with the support for the treads routed into the stringer.
- 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 spiral stairway. When three steps are used to turn a 90° corner, the middle step is called a kite winderas a kite-shaped quadrilateral.
- Trim – Trim (e.g. quarter-round or baseboard trim) is normally applied where walls meet floors and often underneath treads to hide the reveal where the tread and riser meet. Shoe mouldingmay be used between where the lower floor and the first riser meet. Trimming a starting step is a special challenge as the last riser above the lower floor is rounded. Flexible, plastic trim is available for this purpose, however wooden mouldings are still used and are either cut from a single piece of rounded wood, or bent with laminations Scotia is concave moulding that is underneath the nosing between the riser and the tread above it.
- Flight – A flight is an uninterrupted series of steps.
- 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. There may be only one stringer or the stringers otherwise minimized. Where building codes allow, there may not even be handrails.
- 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 the stair between main floor levels and is typically used to allow stairs to change directions, or to allow the user a rest. A half landing is where a 180° change in direction is made, and a quarter landing is where a 90° change in direction is made (on an intermediate landing). 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.
- 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 that holds the carpet in place where the tread meets the riser, known as a stair rod.
- 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.
- Staircase – This term is often reserved for the stairs themselves: the steps, railings and landings; though often it is used interchangeably with “stairs” and “stairway”. In the UK, however, the term “staircase” denotes what in the U.S. is called “stairway”, but usually includes the casing – the walls, banisters and underside of the stairs or roof above.
- Stairway – This primarily American term is often reserved for the entire stairwell and staircase in combination. though often it is used interchangeably with “stairs” and “staircase”.
- Stairwell – The spatial opening, usually a vertical shaft, containing an indoor stairway; by extension it is often used as including the stairs it contains.
- Staircase tower – A tower attached to, or incorporated into, a building that contains stairs linking the various floors.
Measurements
The measurements of a stair, in particular the rise height and going of the steps, should remain the same along the stairs. The following stair measurements are important
- Therise height or rise of each step is measured from the top of one tread to the next. It is not the physical height of the riser; the latter excludes the thickness of the tread. A person using the stairs would move this distance vertically for each step he takes.
- The tread depth of a step is measured from the edge of the nosing to the vertical riser; if the steps have no nosing, it is the same as the going; otherwise it is the going plus the extent of one nosing.
- The going of a step is measured from the edge of the nosing to the edge of nosing in plan view. A person using the stairs would move this distance forward with each step they take.
- To avoid confusion, the number of steps in a set of stairs is always the number of risers, not the number of treads.
- The total run or total going of the stairs is the horizontal distance from the first riser to the last riser. It is often not simply the sum of the individual tread lengths due to the nosing overlapping between treads. If there are N steps, the total run equals N-1 times the going: the tread of the last step is part of a landing and is not counted.
- The total rise of the stairs is the height between floors (or landings) that the flight of stairs is spanning. If there are N steps, the total rise equals N times the rise of each step.
- The slope or pitch of the stairs is the ratio between the rise and the going (not the tread depth, due to the nosing). It is sometimes called the rake of the stairs. The pitch line is the imaginary line along the tip of the nosing of the treads. In the UK, stair pitch is the angle the pitch line makes with the horizontal, measured in degrees. The value of the slope, as a ratio, is then the tangent of the pitch angle.
- Headroomis the height above the nosing of a tread to the ceiling above it.
- Walkline– for curved stairs, the inner radius of the curve may result in very narrow treads. The “walkline” is the imaginary line some distance away from the inner edge on which people are expected to walk. Building code will specify the distance. Building codes will then specify the minimum tread size at the walkline.