(overview of Approved document K – Stairs Ramps and Guards)[13]Approved document K categorises stairs as ‘Private’, ‘Institutional or assembly’ and ‘other’When considering stairs for private dwellingsBuilding regulations are required for stairs used where the difference of level is greater than 600 mm (23.6 in)Steepness of stairs – Rise and Going – Any rise between 155 and 220 mm (6.1 and 8.7 in) used with any going (tread) between 245 and 260 mm (9.6 and 10.2 in) or any rise between 165 and 200 mm (6.5 and 7.9 in) used with any going between 223 and 300 mm (8.8 and 11.8 in)Maximum Rise 220 mm (8.7 in) and Minimum Going 220 mm (8.7 in) 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 mm (21.7 and 27.6 in)Construction of steps – Steps should have level treads, they may have open risers but if so treads should overlap at least 16 mm (0.6 in). 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 100 mm (3.9 in) diameter sphere cannot pass though the opening in the risers in order to prevent children from sticking their heads through them and potentially getting stuck.Headroom – A headroom of 2 m (78.7 in) 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 stairs in shops or assembly building. There is no requirement for private stairs. In practice there will be fewer than 16 steps as 16 x 220 mm (8.7 in) gives over 3.5 m (137.8 in) total rise 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 mm (15.7 in) across the whole landingTapered steps – There are special rules for stairs with tapered steps as shown in the image Example of Winder Stairs aboveAlternate tread stairs can be provide in space saving situationsGuarding – Flights and landings must be guarded at the sides where the drop is more than 600 mm (23.6 in). As domestic private stairs are likely to be used by children under 5 the guarding must be constructed so that a 100 mm (3.9 in) 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 (2.1 lbf/in).Industry guidance on designing a staircase to UK Regulation and Standards.US requirementsAmerican building codes, while varying from State to State and County to County, generally specify the following parameters:[14][15][16]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).[17]Riser-Tread formula: Sometimes the stair parameters will be something like riser plus tread equals 17–18 inches (432–457 mm);[18] another formula is 2 times riser + tread equals 24.6 inches (625 mm), the length of a stride.[5] 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;[5] 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).[19] 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).[5]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 handrailsNot 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 TAS) do not allow open risers on accessible or egress stairs.[20]