STAIRCASE

Staircase The steps of stair may be constructed as a series of horizontal open treads with a space between the treads(enclosed steps) with a vertical face between the treads, called a riser. The horizontal surface is described as the tread and the vertical or near vertical face as the riser. Horizontal treads with a space between them is often described as an open riser stair.

With enclosed steps, the treads usually project beyond the face of the riser, while nosing make surface of tread more practicable. Rise describes the distance measured vertically from the surface of one tread to the surface of the next. Going describes the distance measured horizontally, from the face of the nosing of one riser to the face of the nosing of the next riser. The dimensions of the rise and going of steps determine whether a stair is steep or shallow.

Classification of staircase Type of stair Characteristics Standard location Straight flight stair Stairs run straight in plan view Storey shop houses Quarter turn stair Two steps that run at right angles to look at plan view Residential and public buildings Half turn stair Two steps that run parallel but opposite at a plan view Geometrical stair Trail tread looks acute on plan view Public buildings

Straight flight stair Rises from floor to floor in one direction with or without an intermediate landing. Most economical use of straight flight, avoid using landings.

Quarter turn stair Rises to a landing between two floors, turns through 90, then rises to the floor above. This type of staircase was much used in the two floor semi-detached houses.

Half turn stair Rises to a landing between floors, turns through 180 degree, then rises parallel to the lower flight to the floor above. The landing is described as a half space or half turn landing. A half turn stair is often described as a ‘dog leg’ stair because it looks somewhat like the hind leg of a dog in section. This is the most common arrangement of stairs, using half turn stair a person can access and escape from similar floors.

Geometrical Stairs Geometrical stairs are constructed with treads that are tapered on plan. Two types of geometrical stairs : Spiral (helical) & circular (ellipse). Spiral (helical) stair, with the tapered treads around a centre supports. Ellipse, an open well circular stair as part of an ellipse.

Spiral (helical) stair with the treads tapering to a central, vertical support is the most economical way of planning a stair as it takes up little floor area. This type of stair is difficult to use and may be dangerous to the very young or elderly because the treads taper sharply to the central post. These stairs are used where space is limited for access to an intermediate floor of one room.

Circular or elliptical stairs are constructed around a generous open well with the treads having a shallow taper towards the well. The stairs are extravagant in the use of space. Used as a feature for grand means of access in large buildings.

FUNCTIONAL REQUIREMENTS STRENGTH AND STABILITY SAFETY IN USE FIRE SAFETY

Strength & Stability A stair and its associated landings serves much the same function as a floor in the support of the occupants of a building, with the stepped inclined plane of flights serving as support for movement between floor. The requirements for strength and stability in supporting dead and imposed loads for floors apply equally to stairs.

Safety in use The practical guidance in Approved Document K to the Building Regulations is concerned with the safety of users in determining the rise, going and headroom of stairs and the dimensions of handrails and guarding.

Fire Safety A stair should be constructed of materials that are capable of maintaining strength and stability for a period of time sufficient for those in a building to escape to the outside. The size of the steps and the width of the stair should be adequate for the safe escape of those in the building.

Recommended rise and going for stairs Private stair for one dwelling. -Any rise between 155 mm and 220 mm maximum used with any going between 245 mm and 260 mm or -Any rise between 165 mm and 200 mm used with any going between 223 mm and 300 mm. Institutional and assembly stair serving a building where a substantial number of people are gathered. -Any rise between 135 mm and 180 mm maximum used with any going between 280 mm minimum and 340 mm.

Other stairs in all other buildings -Any rise between 150 mm and 190 mm maximum used with any going between 250 mm minimum and 320 mm. The steeper stair is accepted for houses because the occupants are familiar with the stair and a shallow stair would occupy more area on plan and thus reduce the available living area.

Material Stairs may be constructed of timber, stone, reinforced concrete or metal, with timber and stone being the traditional materials used. Steel and reinforced concrete following the industrial revolution.

Timber Staircase A staircase, which is a stair with treads and risers constructed from timber is the traditional stair for houses of two or more floors where the need for resistance to fire does not dictate the use of concrete. Landings are constructed on site and the flights are fixed in position between landings and floors. The members of the staircase flight are string (or stringers), treads and risers. The members of the flight are usually cut from timbers of the following sizes: treads 32 or 38 mm. risers 19 or 25 mm and strings 38 or 44 mm.

Reinforced concrete Staircase A reinforced concrete stair, which has better resistance to damage by fire than the conventional timber staircase, is used for access and means of escape stairs in most buildings of more than three or four storey. The width, rise, going and headroom for these stairs and the arrangement of the flights of steps is the same as for timber stairs.

Stone Staircase The traditional stone stairs were constructed of steps of natural stone of rectangular or triangular section built into an enclosing wall so that each stone was bedded on the stone below in the form of a stair. The steps were either of uniform rectangular section, rectangular section or triangular section. Landings were constructed with one or more large slabs of natural stone built into enclosing walls and bearing on the step below. Because of the scarcity and cost of natural stone, this type of step is now made of cast stone or cast concrete which is usually reinforced and cast in the same sections.

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