Spiral Staircase Measurements and Dimensions - What You Need To Know

In this article we talk about the measurements and dimensions necessary for a spiral staircase in the UK.

What is the Ideal Spiral Staircase Opening Size?

This is an extremely popular question, and the general rule of thumb is that the opening for spiral staircase should be at least 100mm larger than the diameter. This can be a square opening in the floor or a circular cut out.

This 100mm all around the diameter allows for a 50mm ‘knuckle’ gap between the handrail and the floor as you pass though the opening and between the handrail and any surrounding walls.

When viewed from above the entire spiral is situated within the opening. For example - if you need a 1500mm diameter spiral staircase the opening should be at least 1600 x 1600mm finished or a 1600mm finished diameter.

Spiral Staircase Myths

A common misconception is that the centre column adjoins the floor edge. Whilst this is possible to manufacture, it would produce either an extremely steep spiral rotating 180 degree (which would not conform with the building regulations), or a spiral that would have headroom issues with several treads under the ceiling below.

Spiral Staircase Options

If the length of the opening is large enough and the spiral has a big enough diameter it is sometimes possible to off centre the centre column and produce a stunted small platform level with the floor. This only works in certain circumstances and would be dependent on the floor to floor height/ number of steps needed.

Spirals are a great solution when accessing an upper level but do require a certain size of opening to work. When it comes to a spiral staircase opening size, always go for an opening 100mm larger than the diameter.

What Size Diameter Do You Need For a Spiral Stair?

When it comes to spiral staircase dimensions, what size the diameter should be is an extremely common question in which there is no straight forward answer as it depends on the usage of the staircase. The requirements for spiral staircases in the UK are described in British Standard 5395. This groups spiral stair applications into categories A – E, with A being a lowly used secondary domestic spiral and E being a widely used fully public spiral.

This document specifies the maximum height of each step, the minimum going (depth) of each step and crucially, to answer this question, the clear walking width. Logically, the more people who are going to be using the spiral, the larger the diameter and the more comfortable it will be to ascend.

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. 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.

Make The Most of Your Space

If there is space available, it is always worth opting for as large a diameter as possible. Use common sense and think about how often you might use the stair, how young or old the users might be and the type and size of furniture you might need to carry up or down.

The decision on spiral staircase diameter rests with the building inspector involved with the project and they will specify which category is required. The BS5395 is there as a guide and can be sometimes be over-ruled by the local authority.

Darin is a marketing manager for Complete Stair Systems, who are a supplier of spiral staircases and modern stairs.