Spiral Staircase Diameter For Domestic Spiral Staircases
These spirals are designed to be used by individuals ‘generally familiar with the stair’ and are classed as ‘secondary’ or ‘primary’.
A secondary spiral stair assessing a loft, basement, or mezzanine will require a 600mm clear tread width.
A primary spiral staircase within a dwelling will need an 800mm clear tread width.
As the diagram below illustrates, the clear tread width does not refer to the radius – the centre column and handrails must be factored in to establish the actual diameter.
This diameter will alter slightly depending on the diameter of the centre column and the handrail but is generally 1400mm for a secondary and 1800mm for a primary spiral.