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Spiral Staircase Dimensions for Cast Spiral Staircases

17 November 2014

Cast Building Regs

BS 5395 PART II can be a little intimidating for anyone who does not have to use them on a regular basis.   There is so much scope for different interpretation that it can be misleading and cause unnecessary confusion and distress for clients to make the right decision.

With that in mind British Spirals & Castings have put together this guide.


Is My Staircase Subject to Building Regulations?

We help clients establish is whether the staircase is subject to the Building Regulations as this will determine the choice of sizes available to you. Normally this is simply established by understanding what it is that you are trying to achieve.  For example, if you are making structural changes to the property or wishing to extend or add to the property external then normally planning consent will be required.  Therefore it is implied that Building Regulation requirements will also need to be meet.

However, if you are wishing to put in a staircase to access an established room within your property it may not be necessary to seek planning consent. Your local planning authority will be able to give more guidance on this.

What to Do If Your Staircase Needs Building Regulations?

Assuming that you spiral staircase is subject to Building Regulations, there are four main requirements that need to be meet.

  1. Firstly, is the clear width of the spiral stair tread, this is the measurements between the inside of the centre pole and the inside of the handrail. A common mistake made by clients and architects alike is that they understand this measurement to be half the diameter of the spiral staircase and do not allow for the handrail and centre pole.
  2. The second requirement is the centre going of the tread, which is the measurement from the centre point of the tread from the nosing of one tread to the nosing on the other.
  3. The third is that there is no gap on the staircase more than 100mm.
  4. Finally, at any point on the spiral you will need a minimum of 2000mm of headroom. On a spiral staircase, each rise will be between 200 and 220mm to ensure that this last requirement is achieved as you walk up and under the staircase. This is often overlooked when a staircase is being used to access a room with an apex roof.

So What Are The Measurements Required for Different Situations?

A spiral staircase will tend to be used in one of three situations:

  • Access to one habitable room
  • Access to more than one habitable room
  • Secondary access to an area or room.

This final category is usually when a client wants to provide access to the garden from an upper level, or is providing access to one area of the house. This can also be access for the main staircase. Let’s take each of these in turn.

Using a Spiral Staircase to Access One Habitable Room

A habitable room is defined as a space used for living, sleeping, eating, or cooking, or combinations thereof.  This does not include bathrooms, closets, halls, storage rooms, utility and similar spaces. If your staircase is accessing a lounge and/or kitchen then larger stairs are normally required under the Building Regulations.

This is normally known as a Category A staircase.

The minimum requirements

  • 600mm clear width
  • A centre going of 145mm.
  • This would be a minimum of a 1370mm diameter spiral in any of the cast aluminium ranges.
  • You would require 3 balusters per tread or a baluster and infill baluster depending on the look that you wish to achieve to reduce the gaps between the balusters to less than 100mm.

Using a Spiral Staircase to Access More Than One Habitable Room.

This is normally known as a Category B staircase.

The minimum requirements

  • 800mm clear width (900mm in Scotland) and a centre going of 190mm.
  • minimum of an 1830mm diameter (2083mm in Scotland) spiral in any of the cast aluminium ranges.
  • 3 balusters per tread or a baluster and infill baluster depending on the look that you wish to achieve to reduce the gaps between the balusters to less than 100mm.

Using a Spiral Staircase to Provide Secondary Access

If a staircase is providing secondary access to an area, or is accessing an area not classed as a habitable room, then there is no clear width and centre going requirements. This allows clients to use the smaller diameters. However, there is still a need to ensure that there is:

  • No gap more than 100mm on the spiral and therefore extra balusters or infill balusters are required on these staircases.

There may also be a need to have:

  • A riser bar on the tread to reduce the gap between treads to less than 100mm.

(On any spiral from 1220mm upwards this will not be needed as the design of our treads have a front fascia which ensures that the minimum gap condition is met).

If your spiral staircase does not need to comply with Building Regulations then you have a free run on the width of the staircase that you can put in.   It is your choice whether or not you wish it to comply with the 100mm sphere rule.   Many clients see this as an important safety aspect, therefore they choose to add extra balusters to the basic staircase to reduce potential gaps between the balusters.

You may ask why SOME of our spiral staircases do not comply with the British Building Regulations.  This is because we supply to clients all over the world, many countries have less stringent requirements and therefore we cater for all client’s needs.

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