“What floor opening size do I need for a spiral staircase?”
This is a question we get asked a lot, and the general rule of thumb is that the opening for spiral staircase should be 100mm larger than the diameter. This can be a square opening in the floor or a circular cut out.
This 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.
You can see from the plan sketch on the right that the centre column is in the centre of the opening and is connected back to the edge of the floor with a platform which is generally part of the spiral itself.
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.