Section C Superstructure
A stairway can either consist of steps rising from floor to floor without a break or with steps rising to a landing between floors and further steps to the next floor. A straight flight of parallel steps is the most common type of stairs.
Flight – Step(s) that run consecutively between landings.
Going – The distance between the nose of the thread of the first step and the landing above.
Pitch – The angle between the line of the stairs and the horizontal.
Rise – The height of an individual step from thread to thread.
Tread – Upper surface of a step.
String – Sloping board at each end of the threads, which carry the threads and risers of a stairs. There can be wall strings and outer strings, and these can be closed strings or cut strings.
Rise and going consistency
There must be consistency between the rise and going in any flight of stairs. One flight should never be more than 16 steps.
Diagram C155 - Typical flight of stairs and measurement details
Measuring Head Room
Diagram C156 - Minimum headroom required along a flight
The method of measuring the head room for a flight of stairs can be seen in the diagram above. Stairs should achieve a minimum head height of 2m.
Rise and Going Relationship and Stairs Width
The measurement of 2 R+G is used to ensure the proportion of steps is appropriate. This value ideally should be 600 mm, and always be between 550 mm and 700 mm.
Min going – 220 mm (250 mm optimum)
Max rise – 220 mm (175 mm optimum)
Max angle of pitch – 42° (35° optimum)
The minimum clear width of a stairs is 800 mm as outlined in Technical Guidance Document K of the Building Regulations. Handrails and other obstructions must be outside the 800 mm minimum. Guidance should also be sought from Technical Guidance Document M of the Building Regulations with respect to the minimum required width of stairs.
There must be a landing at the bottom and top of every flight. In a flight that goes to a door, a landing is not required if the flight is less than 600 mm and the door slides open.
The going and width of a landing must be at least greater than the smallest width of the stairs. Where a door opens onto a landing the door must be positioned so that the nose of the first step is a full width of the flight from the swing of the door.
For domestic construction, this distance can be reduced to greater than 400 mm.
Diagram C157 - Compliant landing detail in domestic situations
Handrails must be included on at least on one side of a stairs if it is 1000 mm or less; a handrail may not be necessary on the bottom 2 steps in a domestic construction. The handrail may form the top of a guarding if the height is suitable.
Correct design ensures:
Firmly supported loads
Ease of grip
Virtually no risk of injury to the hand due to trapping
For the entire length, hand freedom is ensured
Diagram C158 - Positioning of handrails along a flight
Construction of Timber Staircases
String: Inclined member provides support to the risers and threads.
Closed string: Houses threads and risers in the parallel edges in the outer string.
Diagram C159 - Typical closed string stair detail
Diagram C160 - Typical underside of risers detail
Stairs must be guarded on both sides in all cases where the rise is greater than 600 mm.
A wall, a screen, a railing, or a balustrade is considered a suitable guard.
Guarding should be designed to eliminate the risk of accidents when constructed.
BS 6262-4: 2005 Glazing for buildings Code of Practice for safety related human impact outlines the recommendations pertaining to guarding containing glazing.
Guarding should be designed so that it cannot be easily climbed by children.
Diagram C161 - Guarding that is not appropriate for use
- The design of guarding should be such that a 100 mm diameter sphere cannot pass through any of the openings as detailed below.
Diagram C162 - Minimum guarding requirements
It is important to ensure that when a cut string stair is provided within a dwelling the space formed by the balustrade, tread and riser is limited. It is important to ensure that the space between the bottom edge of the balustrade and the noising line of the stair is no more than 50mm.
Diagram C163 - Minimum requirements for cut string balustrade
Guarding is required at the sides of:
A raised floor, where the level difference is 600mm or more.
Any place where people may have access excluding access for maintenance or repair only.
The minimum height the guarding is required to achieve will differ depending on its location, details of which have been provided in the table below.
Table C21 - Minimum height requirements for guarding
Diagram C164 - Measuring the height of guarding - balustrade/railing
Diagram C165 - Measuring the height of guarding - solid guarding
It is also important to ensure that guarding has been designed to cope with the relevant imposed loads as detailed in the following table.
Table C22 - Minimum imposed loading which guarding must be able to withstand
NOTE: Assume the uniformly distributed line load acts at 1.1 m above finished floor level (datum) during design even if the actual height for the guarding is different.
Guarding to Glazing
Guarding is required in any window in which the cill level is less than 800 mm above floor level. Guarding should be effective if the window is open or closed. Safety glass may be used as an alternative to the barrier type guarding as long as the safety glass is in accordance with BS 6262 - Part 4: 2018.
Diagram C166 - Minimum guarding requirements at windows
Critical Glazing Locations
Glass that must break safely, resist impact, or be protected by permanent guarding is known as robust glazing. This type of glass must be in accordance with the requirements in BS 6262: Part 4 and be marked in accordance with I.S. EN 12600: 2002 and should be used in the locations illustrated. If the width of the pane is less than 250 mm or the area of the pane is less than 0.5 m2, small panes of 6 mm annealed glass can be used in critical areas.
Diagram C167 - Typical areas where robust glazing is required
Diagram C168 - Maximum permitted area for the use of 6mm annealed glass