SPIRALSTAIR builds a spiral stair as real 3D surfaces — treads winding round a centre column, climbing to a given height over a given sweep, with a railing.
What SpiralStair does
Two railing treatments. Panels makes the treads one surface and the inner and outer railings separate panels of a stated thickness — use this when the railing is a solid balustrade you may want to hide, colour or take off separately. Continuous makes the tread and its railing upstands one unbroken surface, which reads as a folded plate stair and is lighter to carry.
Nothing in AutoCAD draws this. Modelling it by hand means arraying a tread about an axis while also raising it, which ARRAY will not do in one pass.
How to use it
- Load the routine with
APPLOAD, or put it on your support file search path. - Type
SPIRALSTAIR. - Pick the centre and give the inner and outer radii, the height and the sweep.
- Choose panel or continuous railings.
How it works
Each tread is one row of points around the spiral. Walking up the stair, a row is generated at each angular step and added to a growing point list. The whole list is then handed to 3DMESH in one go, which stitches the rows into a continuous surface.
That is why the row point-order matters and is preserved exactly. 3DMESH reads the list as a grid, M rows by N columns, and any change to the order twists the surface.
Each finished mesh is then flagged closed in the N direction, so the surface wraps rather than leaving a seam down the stair.
Direction and sweep. A positive height climbs, a negative one descends — useful for drawing a stair down to a basement from the floor above. The sweep is the angle turned between the first and last tread, so 360 gives a full turn and 270 the common quarter-short spiral.
Notes and limits
- A negative height descends.
- Panels can be hidden separately; a continuous surface cannot.
- This is geometry, not a compliant stair. Check going, rise and headroom against your code.
- One undo group covers the whole stair.
Download and details
| Name | SpiralStair — build a spiral stair as real 3D surfaces |
| Download | SpiralStair.lsp — 12.1 KB, plain AutoLISP source. Downloads directly; no zip to unpack. |
| Type | AutoCAD AutoLISP routine |
| Command | SPIRALSTAIR |
| Requires | nothing beyond a CAD platform with AutoLISP. |
| Source size | 12.1 KB, 292 lines |
| Error handling | Yes — a *error* handler restores every system variable it changed, on cancel as well as on error. |
| Undo | The whole operation is wrapped in a single undo group, so one U reverses all of it. |
| Compatibility | AutoCAD (any release with AutoLISP), BricsCAD, ZWCAD, GstarCAD, ProgeCAD and other IntelliCAD-based platforms. AutoCAD LT needs a LISP enabler. No .NET, no ObjectARX, no installer. |
| Author | YZ, August 2026 |
| Licence | Free to use, supplied “as is” with no warranty. |
References
- STAIRRUN LISP — a straight flight
- STAIRPAN LISP — stair pan details
- HELIX3D LISP — the helix a handrail follows
- More free AutoLISP routines on this site
- Wisey’s Steel Shapes — free structural steel section drawing program