Spiral Staircase Dimensions – Wooden Spiral Staircases
BS 5395 PART II of Building Regulations is the part of the building regulations that governs the requirements that need to be met for spiral staircases. They can be a little intimidating to someone who does not have to use them on a regular basis and there is so much scope for different interpretation that it can sometimes be misleading.
Assuming that your spiral staircase is subject to Building Regulations, there are four main requirements that need to be meet.
- Clear Width – this is the measurements between the inside of the centre pole and the inside of the handrail.
- Centre going – the measurement from the centre point of the tread from the nosing of one tread to the nosing on the other.
- No gap on the staircase large enough for a 100mm sphere ball to fit through
- Sufficient headroom clearance on the staircase. At any point on the spiral you will need a minimum of 2000mm of headroom.
A solid timber spiral staircase will tend to be used for an internal application and due to the cost of the staircase tend to be used in one of two situations; to provide access to one habitable room such as a bedroom or up to mezzanine area or to provide access to more than one habitable room usually as the main staircase in the house.
1.Access to one habitable room.
A habitable room is defined as a space used for living, sleeping, eating, or cooking, or combinations thereof, but not including bathrooms, closets, halls, storage rooms, utility and similar spaces. If your staircase is accessing a lounge and/or kitchen then the larger stairs are normally required under building regulations.
This is normally known as a Category A staircase. The minimum requirement is a 600mm clear width and a centre going of 145mm. This would be a minimum of a 1500mm diameter spiral in any of the solid timber ranges. All staircases come with 3 balusters per tread whether wooden or cast to ensure that there is no gap more than 100mm on the staircase and a riser bar or solid risers to reduce the gaps between the treads depending on the style that is chosen. The centre column is chunkier than that of the cast iron staircases which is why the diameter is larger than one would expect. The centre column is usually 170mm in diameter on these staircases and then handrails are 45mm wide.
2. Access to more than one habitable room.
This is normally known as a Category B staircase. The minimum requirement is an 800mm clear width (900mm in Scotland) and a centre going of 190mm. This would be a minimum of an 1900mm diameter (2100mm in Scotland) spiral in any of the cast aluminium ranges. Again the staircase comes with 3 balusters per tread and the relevant riser bars. The tread angle on theses size staircases can vary to meet individual requirements between 26 and 22.5 degrees.
As with our cast aluminium staircases, if there is not a requirement for Building Regulations then clients may choose to put a smaller diameter in but we always advise clients to put in the maximum they can to ensure that because of the larger centre column the width of the spiral does not become too tight. The smallest diameter that we can do in the solid timber range is 1200mm diameter.