Stairway to heaven?

Spiral and helical (centreless) stairs are attractive in several ways

• They can be extremely elegant and visually satisfying. This is partly the spiral shape itself and partly the visual connection which can be created between the two or more floors. They can also introduce an element of novelty.
• Sometimes they will allow stairs to fit into a space which would be difficult for conventional stairs. However it can work the other way because of the greater width of the treads which is usually required by the Building Regulations. Read on.

 Considerations 

There are several constraints to take into account and they involve the slightly complex geometry of spiral stairs:

• Is there enough space for them to fit in?
• Will the turn of the stairs allow for the upstairs landing to be in the right place?
• Will the upstairs landing work when headroom over the stairs is taken into consideration?
• Are half landings required?
• If there is a centre pole, how is it supported?
• If it is centreless then what supports the whole of the stair structure
• Is fire proofing between storeys an issue?
• Do you want a factory made kit system or a custom design?

Space requirements

Most of the factory made systems have good on-line information about the dimensions of their various models and you can establish pretty quickly whether there is enough space.

If you are wanting custom made spiral stairs then the Building Regulations are quite complicated and there are some calculations to do. Basically the regulations are there to make them as safe as normal straight stairs in terms of risers, going, headroom, guarding (handrails etc.), numbers of steps in a run, landings and average width of treads.

 How much turn?

There is a complex relationship between the going, the riser and the width of the stairs and this determines how much the stair turns. It is, for instance, possible to design a narrow spiral staircase to rise by 2.5 metres with only a bit more than half a turn. But the question arrises as to whether you are heading in the right direction when you reach the top. If not you may need a large and awkward landing to get facing the right way. If you have wider going (treads) then you will complete more of a circle.

Headroom

The headroom you need over the stairs may eat into the area of the landing above. There are minimum areas stipulated by the regulations.

Half landings

Half landings may be necessary in some cases such as when adjacent floor levels differs by something other than a storey hight. This will then involve a specially made half landing which may not work well with a kit stairs.

Support

Each tread needs supporting and fixing at both ends. This can be done a number of ways.

If there is a centre pole it can support the centre end of the treads but it also needs fixing top and bottom. Usually the bottom of the pole has a plate which is fixed directly to the floor. The top of the pole can go up to the floor above (or a structural element incorporated in the ceiling) or it can be fixed to the upper floor, in which case it needs a lateral support which also serves as the upper landing. This is the most usual configuration.

The outer ends of the treads are often fixed to each other using the ballustrading which supports the handrail. This gives added strength and rigidity to the whole structure.

If the stairs are centreless then there are basically three ways  to support the treads

• a support wall under the tread ends
• a structural curved string to both sides of the steps, rigidly fixed at the top and bottom
• a method of rigidly fixing succeeding treads to each other at both ends so that they effectively form a string similar to stairs with a centre pole.

It may be possible to support the outer ends of treads on surrounding walls either by fixing to them or cantilevering out from them. If they are cantilevered then thestairs can be centreless or there can be a pole, or the steps can be stacked on top of each other.

Stairs and the regulations

Below are extracts from the Building Regulations where stairs in houses are termed ‘Private stairs’

Because the relationship between the rise and the going is quite complicated there are 3 methods of achieving the correct result but they all rely on the fact that the pitch of the steps must not be greater than 42°.

This is how it is measured:

The three ways to calculate it are:

• The maximum rise for steps is 220mm and minimum going is 220mm (but of course with the added proviso that it will not be steeper than 42°)
• The second way of working it out is having: 
• Any rise between 155mm and 220mm used with any going between 245mm and 260mm;OR
• Any rise between 165mm and 200mm used with any going between 223mm and 300mm.
• The third way is to make sure that the relationship between the dimensions of the rise and going is that twice the rise plus the going (2R + G) should be between 550mm and 700mm.

Construction of steps

Steps should have level treads. Steps may have open risers, but treads should then overlap each other by at least 16mm. For steps in buildings providing the means of access for disabled people reference should be made to Approved Document M, Access and facilities for disabled people.

All stairs which have open risers and are likely to be used by children under 5 years should be constructed so that a 100mm diameter sphere cannot pass through the open risers.

Headroom (with exemption for loft conversion)

A headroom of 2m is adequate on the access between levels (see Diagram 2). For loft conversions where there is not enough space to achieve this height, the headroom will be satisfactory if the height measured at the centre of the stair width is 1.9m reducing to 1.8m at the side of the stair as shown in Diagram 3.

Width of flights

No recommendations for minimum stair widths are given. Designers should bear in mind the requirements for stairs which:

• form part of means of escape. Reference should be made to Approved Document B: Fire safety;
• provide access for disabled people. Reference should be made to Approved Document M: Access and facilities for disabled people.

Length of flights 

Stairs having more than 36 risers in consecutive flights should make at least one change of direction between flights of at least 30° (see Diagram 5).

Landings

Landings should be provided at the top and bottom of every flight. The width and length of every landing should be at least as great as the smallest width of the flight. The landing may include part of the floor of the building.

To afford safe passage landings should be clear of permanent obstruction. A door may swing across a landing at the bottom of a flight but only if it will leave a clear space of at least 400mm across the full width of the flight (see Diagram 6). Doors to cupboards and ducts may open in a similar manner over a landing at the top of a flight (see Diagram 7). For means of escape requirements reference should be made to Approved Document B: Fire safety.

Landings should be level unless they are formed by the ground at the top or bottom of a flight. The maximum slope of this type of landing may be 1 in 20 provided that the ground is paved or otherwise made firm.

Special stairs - Tapered treads

For steps with tapered treads the going should be measured as follows:

• if the width of flight is narrower than 1 m measure in the middle
• if the width of flight is 1 m or wider measure 270mm from each side

The going of tapered treads should measure at least 50mm at the narrow end.

Where consecutive tapered treads are used a uniform going should be maintained.

Where a stair consists of straight and tapered treads the going of the tapered treads should not be less than the going of the straight flight – these treads should satisfy paragraphs 1.1 to 1.5.

Stairs designed to BS 585-1:1989 Wood stairs.

Specification for stairs with closed risers for domestic use, including straight and winder flights and quarter or half landings, will offer reasonable safety.

Also:

Stairs designed in accordance with BS 5395-2:1984 Stairs, ladders and walkways.

Code of practice for the design of helical and spiral stairs will be adequate.

Stairs with goings less than shown in this standard may be considered in conversion work when space is limited and the stair does not serve more than one habitable room.

Handrails for stairs

Stairs should have a handrail on at least one side if they are less than 1m wide. They should have a handrail on both sides if they are wider. Handrails should be provided beside the two bottom steps in public buildings and where stairs are intended to be used by people with disabilities. See Approved Document M: Access and facilities for disabled people. Elsewhere handrails need not be provided beside the two bottom steps.

In all buildings handrail height should be between 900mm and 1000mm measured to the top of the handrail from the pitch line or floor.

Handrails can form the top of a guarding if the heights can be matched.

Guarding of stairs

Flights and landings should be guarded at the sides (see Diagram 11) in dwellings – when there is a drop of more than 600mm;

Except on stairs in a building which is not likely to be used by children under 5 years the guarding to a flight should prevent children being held fast by the guarding. The construction should be such that:

• a 100mm sphere cannot pass through any openings in the guarding; and
• children will not readily be able to climb the guarding.

The height of the guarding itself should be as shown in the diagram 11 below

Pedestrian guarding

There may be other situations around stairs where guarding is required:

Siting

Guarding should be provided where it is reasonably necessary for safety to guard the edges of any part of a floor (including the edge below an opening window), gallery, balcony, roof (including rooflights and other openings), any other place to which people have access and any light well, basement area or similar sunken area next to a building. Guarding should also be provided in vehicle parks, but not on any ramps used only for vehicle access. Guarding need not be provided to such places as loading bays where it would obstruct normal use.

Design

Any wall, parapet, balustrade or similar obstruction may serve as guarding. Guarding should be at least the height shown in Diagram 11. Guarding should be capable of resisting at least the horizontal force given in BS 6399-1:1996. Where glazing is used in the guarding, reference should be made to Approved Document N: Glazing – safety in relation to impact, opening and cleaning.

For further guidance on design of barriers and infill panels, reference should be made to BS 6180:1995Code of practice for protective barriers in and about buildings.

Where buildings are likely to be used by children under 5 years the guarding should prevent children being held fast by the guarding. The construction should be such that a 100mm sphere cannot pass through any opening in the guarding and so that children will not readily be able to climb it. Horizontal rails for such guarding should be avoided.