Stairs & Railings
Thu, 03/26/2009 - 15:15 — JohnSopher
Lets talk about Stairs, Steps, and Rails
Components and terminology
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 "width" is measured from the outer edge of the step to the vertical "riser" between steps.
- 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 horizontally, the total "run" length of the stairs is not simply the sum of the tread lengths, 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 semi-circle 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 bullnose can be used when both sides of the stairs are open.
- 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 winder as a kite-shaped quadrilateral.
- 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.
- 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 moulding may 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.
Staircase between levels at Cabot Circus shopping centre, Bristol, England. A sitting area is provided on the right of the staircase proper.
The railing system
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; there is often a railing on both sides, sometimes only on one side or not at all, on wide staircases there is sometimes also one in the middle, or even more. The term "banister" is sometimes used to mean just the handrail, or sometimes the handrail and the balusters or sometimes just the balusters.
- Volute - a handrail for the bullnose step that is shaped like a spiral. Volutes may be right or left-handed depending on which side of the stairs they occur when facing up the stairs.
- Turnout - instead of a complete spiral volute, a turnout is a quarter-turn rounded end 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 a "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. However, this means the first and second balusters are manufactured separately and cannot be interchanged. Balusters without decorative elements can be interchanged.
- 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.
- 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.
Historical photo a of staircase in the Ford plant in Los Angeles with a double bullnose and two volutes. The photo also shows an intermediate landing as part of this U-shaped stair.
- 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. In modern homes, it is common to have hardwood floors on the first floor and carpet on the second. The homeowner should consider using hardwood nosing in place of carpet. Should the carpet be subsequently replaced with hardwood, the balcony balustrade may have to be removed to add the nosing.
- 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. 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.
- 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 specialized bar 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 U.S. is called "stairway", but usually includes the casing - the walls, bannisters and underside of the stairs or roof above.
- Stairway - this term is often reserved for the entire stairwell and staircase in combination; though often it is used interchangeably with "stairs" and "staircase".Measurements
- The rise height 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.
- The tread depth or length is measured from the edge of the nosing to the vertical riser. It is sometimes called the going.
- The total run 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.
- The total rise of the stairs is the height between floors (or landings) that the flight of stairs is spanning.
- The slope of the stairs is the total rise divided by the total run (not the individual riser and treads due to the nosing). It is sometimes called the rake or pitch of the stairs. The pitch line is the imaginary line along the tip of the nosing of the treads.
- 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.
- To avoid confusion, the number of steps in a set of stairs is always the number of risers, not the number of treads.
The easiest way to calculate the rise and run is to use a stair stringer calculator.
Ergonomics and building code requirements
Ergonomically and for safety reasons, stairs have to have certain measurements in order for people to comfortably use them. Building codes will typically specify certain measurements so that the stairs are not too steep or narrow. Building codes will specify :
- minimum tread length, typically 9 inches (229 mm) including the nosing for private residences. However, most human feet are longer than 9 inches (229 mm), thus people's feet don't actually fit on the tread of the step.
- maximum riser height, typically 8.25 inches (210 mm). Note that by specifying the maximum riser height and minimum tread length, a maximum slope is established. Residential building codes will typically allow for steeper stairs than public building codes.
- minimum riser height: Some building codes also specify a minimum riser height, often 5 inches (125 mm).
- Riser-Tread formula: Sometimes the stair parameters will be something like riser + tread equals 17-18 inches(431 mm - 457 mm)- or another formula is 2 times riser + tread equals 24 inches (610 mm). Thus a 7 inch (178 mm) rise and a ten inch (254 mm) tread exactly meets this code. If only a 2 inch (51 mm) rise is used then a 20 inch (508 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. This makes low rise stairs 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.
- variance on riser height and tread depth between steps on the same flight should be very low. Building codes may specify variances as small as 0.25 inches (6.4 mm). 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 (37 and 68 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).
- minimum headroom
- 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.
Jacques-François Blondel in his 1771 Cours d'architecture was the first known person to establish the ergonomic relationship of tread and riser dimensions. He specified that 2 x riser + tread = step length.
It is estimated that a noticeable mis-step once in 7,398 uses and a minor accident on a flight of stairs occurs once in 63,000 uses. Some people choose to live in residences without stairs so that they are protected from injury.
Stairs are not suitable for wheelchairs and other vehicles. A stairlift is a mechanical device for lifting wheelchairs up and down stairs. For sufficiently wide stairs, a rail is mounted to the treads of the stairs. A chair or lifting platform is attached to the rail. A person on the chair or platform is lifted as the chair or platform moves along the rail.
Stairs can take a large number of forms, combining winders and landings.
The simplest form is the straight flight of stairs, without any winders nor landings. It is not often
used in modern homes because:
- the upstairs is directly visible from the bottom of a straight flight of stairs.
- it is potentially more dangerous in that a fall is not interrupted until the bottom of the stairs.
- a straight flight requires enough space for the entire run of the stairs.
However, a straight flight of stairs is easier to design and construct than one with landings. Additionally, the rhythm of stepping is not interrupted in a straight run, which may offset the increased fall risk by helping to prevent a misstep in the first place.
Most modern stairs incorporate at least one landing. "L" shaped stairways have one landing and usually change in direction by 90 degrees. "U" shaped stairs may employ a single wider landing for a change in direction of 180 degrees, or 2 landings for two changes in direction of 90 degrees each. Use of landings and a possible change of direction have the following effects:
- The upstairs is not directly visible from the bottom of the stairs, which can provide more privacy for the upper floor.
- A fall can be arrested at the landing.
- Though the landings consume total floor space, there is no requirement for a large single dimension, allowing more flexible floorplan designs.
- For larger stairs, particularly in exterior applications, a landing can provide a place to rest the legs.
Spiral and helical stairs
A spiral staircase inside Cremona's Torrazzo
The Tulip Stairs & lantern at the Queen's House, Greenwich.
Spiral stairway seen from below; Melk Abbey, Austria
Spiral stairs wind around a central pole. They typically have a handrail on the outer side only, and on the inner side just the central pole. A squared spiral stair assumes a square stairwell and expands the steps and railing to a square, resulting in unequal steps (larger where they extend into a corner of the square). A pure spiral assumes a circular stairwell and the steps and handrail are equal and positioned screw-symmetrically. A tight spiral stair with a central pole is very space efficient in the use of floor area. A user of these stairs must take care to not step too close to the central pole as it becomes more likely that one or more steps may be missed, especially when going down. Using the handrail will also direct the user to the safer outer portion of the treads.
Spiral stairs in medieval times were generally made of stone and typically wound in a clockwise direction (from the ascendor's point of view), in order to place at a disadvantage attacking swordsmen who were most often right-handed). This asymmetry forces the right-handed swordsman to engage the central pike and degrade his mobility compared with the defender who is facing down the stairs. Extant 14th to 17th century examples of these stairways can be seen at Muchalls Castle, Crathes Castle and Myres Castle in Scotland. Exceptions to the rule exist, however, as may be seen in the above image of the Scala of the Palazzo Contarini del Bovolo, which winds up anti-clockwise.
Developments in manufacturing and design have led to the introduction of kit form spiral stair. 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.
Helical or circular stairs do not have a central pole and there is a handrail on both sides. These have the advantage of a more uniform tread width when compared to the spiral staircase. Such stairs may also be built around an elliptical or oval planform. A double helix is 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 helixes (there is one at Château de Chambord). Fire escapes, though built with landings and straight runs of stairs, are often functionally double helixes, with two separate stairs intertwinned and occupying the same floor space. This is often in support of legal requirements to have two separate fire escapes.
Both spiral and helical stairs can be characterized by the number of turns that are made. A "quarter-turn" stair deposits the person facing 90 degrees from the starting orientation. Likewise there are half-turn, three-quarters-turn and full-turn stairs. A continuous spiral may make many turns depending on the height. Very tall multi turn spiral 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.
Alternating tread stairs
An alternating tread stair (center) between a half-width stair (left) and full-width stair (right).
An alternating tread stair climbing the steep slope of a pinnacle in Pinnacles National Monument, California, USA
Where there is insufficient space for the full run length of normal stairs, alternating tread stairs may be used. Alternating tread stairs allow for safe forward-facing descent of very steep stairs. The treads are designed such that they alternate between treads for each foot: one step is wide on the left side; the next step is wide on the right side. There is insufficient space on the narrow portion of the step for the other foot to stand, hence the person must always use the correct foot on the correct step. The slope of alternating tread stairs can be as high as 65 degrees as opposed to standard stairs which are almost always less than 45 degrees. The advantage of alternating tread stairs is that people can descend face forward. The only other alternative in such short spaces would be a ladder which requires backward-facing descent. Alternating tread stairs may not be safe for small children, the elderly or the physically challenged. Building codes typically classify them as ladders and will only allow them where ladders are allowed, usually basement or attic utility or storage areas not frequently accessed.
The image on the right illustrates the space efficiency gained by an alternating tread stair. The alternating tread stair appearing on the image's center, with green-colored treads. The alternating stair requires one unit of space per step: the same as the half-width step on its left, and half as much as the full-width stair on its right. Thus, the horizontal distance between steps is in this case reduced by a factor of two reducing the size of each step.
The horizontal distance between steps is reduced by a factor less than two if for constructional reasons there are narrow "unused" steps.
There is often (here also) glide plane symmetry: the mirror image with respect to the vertical center plane corresponds to a shift by one step.
Alternating tread stairs have been in use since at least 1888.
Informatin provided by Wikipedia, the free encyclopedia.