Spiral Staircase Geometry

Floor to floor mm Outer radius mm

Centre pole radius mm Handrail intrusion mm

Target riser mm Tread angle °

Slab thickness mm Tread thickness mm

Climbing direction Walkline from pole mm

Min clear width mm Min walkline tread mm

Max riser mm Min headroom mm

Walkline is where people actually put their feet, 305 mm (12 in) out from the narrow edge. A spiral tread is a wedge, so the width you can use depends on where you measure. Limits are editable: set them to your own code.

Risers–

Tread at walkline–

Clear width–

Opening sweep–

Plan

Checks

Unrolled section

Tread schedule mm

Tread	Top level	Walkline depth	Outer depth	Headroom