Stairs

Steps with two anti-slip rubber strips and small nosings

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 (thickness) 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".
• 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. Many building codes require stair nosings for commercial, industrial, or municipal stairs.[3] 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 which usually houses the volute and volute newel turning for a continuous handrail. The curtail tread will follow the flow of the volute.[4]

Neo-Baroque stairs with intricate wooden balustrade

Staircase with double bullnose and two volutes. An intermediate landing is part of this U-shaped stair.

Handrail and carved balusters

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 in 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.[5]
• 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.

Winder stairs with a simple handrail supported by three newel posts

• 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 (sometimes called over-the-post) or post-to-post (or more accurately newel-to-newel). 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 which 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.

Two flights of stairs joined by a landing

• Flight: Any uninterrupted series of steps between floors or levels.[6]
• 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 (on an intermediate landing).[7] 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.[8]
• 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 staircase

• 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.[9] 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.
• 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 US is called "stairway", but usually includes the casing – the walls, bannisters 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.

A quite unusual "variable rise" stairway, which also distorts visual perspective (at The Duomo in Urbino, Italy)

The dimensions of a stair, in particular the rise height and going of the steps, should remain the same along the stairs.[10]

The following stair dimensions are important:

• The rise 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 taken.
• 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 first step is part of a landing.
• 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.
• Headroom is 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.

Comparison of spiral (blue), helix (green), and a conical helix (red) derived from both curves

Perspective foreshortening flattens this upward view of an open-well helical stairway into the appearance of a spiral (Hamburg, Germany)

The term "helical stair" has many synonyms:[12]^: 53

The helical stair is also called the spiral stair, winding stair, circular stair, elliptical stair, oval stair, geometric stair, vis, vice, vis de Saint Gilles, St. Gilles screw, belfry stair, turret stair, caracole, turnpike, cochlea, cockle, corkscrew, and ascensorium. Helical is possibly the least poetic but also the most accurate generic title.

— John Templer, The Staircase: History and Theories (1992)

The term "spiral" has a more narrow definition in a mathematical context, as a curve which lies in a single plane and moves towards or away from a central point, with a continuously changing radius. The mathematical term for the 3-dimensional curve traced where the locus progresses at a fixed radius from a fixed line while moving in a circular motion around it is a "helix". Since the very purpose of a stairway is to change elevation, it is inherently a 3-dimensional path.

Loose everyday usage conflates the terms helical and spiral, but the vast majority of circular stairs are actually helical.[13][14] True spiral staircases would be nonfunctional flat structures, although functional hybrid helical spiral staircases can be constructed. This article attempts to preferentially use the terms "helix" and "helical" to describe circular stairways more clearly and precisely, while reserving the term "spiral" for a curve restricted to a flat plane.

Helical stairs, sometimes referred to in architectural descriptions as vice, wind around a newel (also called the "central pole"). The presence or absence of a central pole or newel does not affect the overall terminology applied to the design of the structure. In Scottish architecture, helical stairs are commonly known as a turnpike stair.

Helical stairs typically have a handrail along the outer periphery only, and on the inner side may have just a central pole. A "squared helical" stair fills a square stairwell and expands the steps and railing to a square, resulting in unequal steps (wider and longer where they extend into a corner of the square). A "pure helix" fills a circular stairwell, and has multiple steps and handrail elements which are identical and positioned screw-symmetrically.

Helical stairs have a handedness or chirality, analogous to the handedness of screw threads, either right-handed or left-handed helical shapes. Ascending a right-handed helix rises counter-clockwise, while ascending a left-handed helix rises clockwise (both as viewed from above).

Industrial helical staircase winding around a central newel

Upwards view of an Art Nouveau helical staircase with a pentagonal core

Gothic helical staircase rises clockwise in St. Elisabeth Cathedral in Košice, Slovakia

A fundamental advantage of helical stairs is that they can be very compact, fitting into very narrow spaces and occupying a small footprint.[12]^: 54 For this reason, they can often be found in ships and submarines, industrial installations, small loft apartments, and other locations where floorspace is scarce.[12]^: 81 However, this compactness can come at the expense of requiring great craftsmanship and care to produce a safe and effective structure.[12]^: 54 By contrast, grand helical stairs occupying wide sweeps of space can also be built, to showcase luxurious funding and elegant taste.[12]^: 56 Architects have used the twisting curvilinear shape as an embellishment, either within or outside of their buildings.[12]^: 58–59

Helical stairs have the disadvantage of being very steep if they are tight (small radius) or are otherwise not supported by a center column. The cylindrical spaces they occupy can have a narrow or wide diameter:

• The wider the helix, the more steps can be accommodated per revolution around the central axis. Therefore, if the helix is large in diameter, due to having a central support column that is strong (and large in diameter) with a special handrail that helps to distribute the load, each step may be longer and therefore the rise between each step may be smaller (equal to that of regular steps). Otherwise, the circumference of the circle at the walk line will be so small that it will be impossible to maintain a normal tread depth and a normal rise height without compromising headroom before reaching the upper floor.
• A small-diameter helix can still have wider treads near the central axis, by making the treads "dance". The narrow end of each tapering wedge-shaped tread is widened, and installed to overlap the adjacent treads above and below.[12]^: 64
• To maintain headroom, some helical stairs with a very short diameter must also have a very high rise for each step. These are typically cases where the stairwell must be a small diameter to fit a narrow space, or must not have any center support by design, or may not have any perimeter support. A tight helical stair with a central pole is very space efficient in the use of floor footprint. However, this type of stairway must be used carefully, to avoid an injurious fall.

"Open well" helical or circular stairs designed by architects often do not have a central pole, but then there usually is a handrail at both sides of the treads. These designs have the advantage of a more uniform tread depth when compared to a narrow helical staircase. Such stairs may also be built around an elliptical or oval footprint,[12]^: 68–72 or even a triangular or pentagonal core. Lacking a central pole, an open well staircase is supported at its outer periphery, or in some cases may be a completely self-supporting and free-standing structure.

An example of perimeter support is the Vatican stairwell or the Gothic stairwell. The latter stairwell is tight because of its location where the diameter must be small. Many helices, however, have sufficient width for normal size treads (8 inches (200 mm)) by being supported by any combination of a center pole, perimeter supports attaching to or beneath the treads, and a helical handrail. In this manner, the treads may be wide enough to accommodate low rises. In self-supporting stairs, the helix needs to be steep to allow the weight to distribute safely down the structure in the most vertical manner possible. Helical steps with center columns or perimeter support do not have this limitation. Building codes may limit the use of helical stairs to small areas or secondary usage, if their treads are not sufficiently wide or have risers taller than 9.5 inches (240 mm).[15]

Double helix staircases are possible, with two independent helical stairs in the same vertical space, allowing one person to ascend and another to descend without ever meeting, if they choose different helices.[12]^: 74 For examples, the Pozzo di San Patrizio allows one-way traffic so that laden and unladen mules can ascend and descend without obstruction, while Château de Chambord, Château de Blois, and the Crédit Lyonnais headquarters ensure separation for social purposes.

Emergency exit stairways, though built with landings and straight runs of stairs, are often functionally double helices, with two separate stairs intertwined and occupying the same floor footprint. This is often in compliance with legal safety requirements to have two independent fire escape paths.

Helical stairs can be characterized by the number of turns that are made. A "quarter-turn" stair deposits the person facing 90° from the starting orientation. Likewise, there are half-turn, three-quarters-turn and full-turn stairs. A continuous helix may make many turns depending on the height. Very tall multi-turn helical staircases are usually found in old stone towers within fortifications, churches, and in lighthouses. Winders may be used in combination with straight stairs to turn the direction of the stairs. This allows for a large number of permutations in designs.

The earliest known helical staircases appear in Temple A in the Greek colony Selinunte, Sicily, to both sides of the cella. The temple was constructed around 480–470 BCE.[16]

When used in Roman architecture, helical stairs were generally restricted to elite luxury structures. They were then adopted into Christian ecclesiastic architecture.[17] During the Renaissance and Baroque periods, increasingly spectacular helical stairways were devised, first deleting walled enclosures, and then deleting a central post to leave an open well.[12]^: 60–74 Modern designs have trended towards minimalism, culminating in helical stairs made largely of transparent glass, or consisting only of stair treads with minimal visible support.[12]^: 67

There is a common misconception that helical staircases in castles rose in a clockwise direction, to hinder right-handed attackers.[18][19] While clockwise helical staircases are more common in castles than anti-clockwise, they were even more common in medieval structures without a military role, such as religious buildings.[20] Studies of helical stairs in castles have concluded that "the role and position of spirals in castles ... had a much stronger domestic and status role than a military function"[20] and that "there are sufficient examples of anticlockwise stairs in Britain and France in [the 11th and 12th centuries] to indicate that the choice must have depended both on physical convenience and architectural practicalities and there was no military ideology that demanded clockwise staircases in the cause of fighting efficiency or advantage".[18]

Developments in manufacturing and design have also led to the introduction of kit form helical stairs. Modular, standardized steps and handrails can be bolted together to form a complete unit. These stairs can be made out of steel, timber, concrete, or a combination of materials.

Staircase between levels at Cabot Circus shopping center, Bristol, England. A sitting area is provided on the right of the staircase proper.

(overview of Approved document K – Stairs, Ladders and Ramps)[30]

The 2013 edition "approved document K" categorises stairs as private, utility and general access

When considering stairs for private dwellings, all the specified measurements are in millimetres.

Building regulations are required for stairs used where the difference of level is greater than 600

Steepness of stairs – rise and going

Any rise between 150 and 220 used with any going between 220 and 300

Maximum rise 220 and minimum going 220 remembering that the maximum pitch of private stairs is 42°. The normal relationship between dimensions of the rise and going is that twice the rise plus the going (2R + G) should be between 550 and 700

Construction of steps

Steps should have level treads, they may have open risers but if so treads should overlap at least 16mm. Domestic private stairs are likely to be used by children under 5 years old so the handrail ballister spacing should be constructed so that a 100mm diameter sphere cannot pass through the opening in the risers in order to prevent children from sticking their heads through them and potentially getting stuck.

Headroom

A headroom of 2000mm is adequate. Special considerations can be made for loft conversions.

Width of flights

No recommendations are given for stair widths.

Length of flights

The approved document refers to 16 risers (steps) for utility stairs and 12 for general access. There is no requirement for private stairs. In practice there will be fewer than 16 steps as 16 x 220 gives over 3500 total rise (storey height) which is way above that in a domestic situation.

Landings

Level, unobstructed landings should be provided at the top and bottom of every flight. The width and length being at least that of the width of the stairs and can include part of the floor. A door may swing across the landing at the bottom of the flight but must leave a clear space of at least 400 across the whole landing

Tapered steps

There are special rules for stairs with tapered steps as shown in the image Example of Winder Stairs above

Alternate tread stairs can be provide in space saving situations

Guarding

Flights and landings must be guarded at the sides where the drop is more than 600mm. As domestic private stairs are likely to be used by children under 5 the guarding must be constructed so that a 100mm diameter sphere cannot pass through any opening or constructed so that children will not be able to climb the guarding. The height for internal private stairs should be at least 900 mm (35.4 in) and be able to withstand a horizontal force of 0.36|kN/m|.

American building codes, while varying from State to State and County to County, generally specify the following parameters:[31]

• Minimum tread length, typically 9 inches (229 mm) excluding the nosing for private residences. Some building codes also specify a minimum riser height, often 5 inches (127 mm).[32]
• Riser-Tread formula: Sometimes the stair parameters will be something like riser plus tread equals 17–18 inches (432–457 mm);[33] another formula is 2 times riser + tread equals 24.6 inches (625 mm), the length of a stride.[10] Thus a 7 inches (178 mm) rise and a 10.6 inches (269 mm) tread exactly meets this code. If only a 2 inches (51 mm) rise is used then a 20.6 inches (523 mm) tread is required. This is based on the principle that a low rise is more like walking up a gentle incline and so the natural swing of the leg will be longer.
• Low rise stairs are very expensive in terms of the space consumed. Such low rise stairs were built into the Winchester Mystery House to accommodate the infirmities of the owner, Sarah Winchester, before the invention of the elevator. These stairways, called "Easy Risers" consist of five flights wrapped into a multi-turn arrangement with a total width equal to more than four times the individual flight width and a depth roughly equal to one flight's run plus this width. The flights have varying numbers of steps.
• Slope: A value for the rise-to-tread ratio of 17/29 ˜ 0.59 is considered optimal;[10] this corresponds to a pitch angle of about 30°.
• Variance on riser height and tread depth between steps on the same flight should be very low. Building codes require variances no larger than 0.1875 inches (4.76 mm) between depth of adjacent treads or the height of adjacent risers; within a flight, the tolerance between the largest and smallest riser or between the largest and smallest tread can not exceed 0.375 inches (9.5 mm).[34] The reason is that on a continuous flight of stairs, people get used to a regular step and may trip if there is a step that is different, especially at night. The general rule is that all steps on the same flight must be identical. Hence, stairs are typically custom made to fit the particular floor to floor height and horizontal space available. Special care must be taken on the first and last risers. Stairs must be supported directly by the subfloor. If thick flooring (e.g. thick hardwood planks) are added on top of the subfloor, it will cover part of the first riser, reducing the effective height of the first step. Likewise at the top step, if the top riser simply reaches the subfloor and thick flooring is added, the last rise at the top may be higher than the last riser. The first and last riser heights of the rough stairs are modified to adjust for the addition of the finished floor.
• Maximum nosing protrusion, typically 1.25 inches (32 mm) to prevent people from tripping on the nosing.
• Height of the handrail. This is typically between 34 and 38 inches (864 and 965 mm), measured to the nose of the tread. The minimum height of the handrail for landings may be different and is typically 36 inches (914 mm).
• Handrail diameter. The size has to be comfortable for grasping and is typically between 1.25 and 2.675 inches (31.8 and 67.9 mm).
• Maximum space between the balusters of the handrail. This is typically 4 inches (102 mm).
• Openings (if they exist) between the bottom rail and treads are typically no bigger than 6 inches (152 mm).
• Headroom: At least 83 inches (211 cm).[10]
• Maximum vertical height between floors or landings. This allows people to rest and limits the height of a fall.
• Mandate handrails if there is more than a certain number of steps (typically 2 risers).
• Minimum width of the stairway, with and without handrails.
• Not allow doors to swing over steps; the arc of doors must be completely on the landing/floor.
• A stairwell may be designated as an area of refuge as well as a fire escape route, due to its fire-resistance rated design and fresh air supply.
• The American Disabilities Act and other accessibility standards by state, such as Architectural Barriers Texas Accessibility Standards (TAS),[35] do not allow open risers on accessible or egress stairs.[36]

• 
  There is no newel at Loretto Chapel's helical staircase (the "Miracle stair") in Santa Fe, New Mexico, United States.
• 
  A helical staircase inside Cremona's Torrazzo, Italy
• 
  Upward view of the Tulip Stairs & lantern at the Queen's House, Greenwich, England
• 
  Helical stairway seen from below; Melk Abbey, Austria
• 
  The wooden helical stairs of the Tour de Sauvabelin in Lausanne
• 
  Tudor staircase, Madingley Hall, Cambridgeshire, England, from below
• 
  The Bramante Staircase, Vatican Museums, showing the two access points at the bottom of the stairs
• 
  Helical stairs at Hotel Astoria, Copenhagen