Stairs
A stair is defined by a walking line drawn from the bottom and a number of risers per segment. Everything else — tread depth, riser height, landing sizes, the soffit — follows from those.
Two shapes, one tool: straight runs with landings, and spirals. The Shape switch in the stair settings decides which one the Stair button draws.
Draw one
Section titled “Draw one”- Click Stair on the toolbar.
- Click the bottom of the flight.
- Click where it turns, or where it ends.
- Double-click to finish.
The cursor is locked into the floor plane after the first click, so you are drawing a plan, not fighting perspective. A blue 2D symbol shows treads, landings and the walking line while you draw, with the temporary 3D body under it.
| Type a number + Enter | total number of risers (before the first turn) |
| Shift | 45° lock on the first segment |
| Esc | step back |
Turns and landings
Section titled “Turns and landings”Each turn creates a landing, and the next flight always runs perpendicular. Which side it turns to follows your cursor.
Click closer than the stair width and you get a U-turn instead: the two landings merge into one and the flights run back alongside each other.
Flight gap is the space between those two flights — the stairwell. Zero by default; give it a value and the U opens up. Everything recomputes: the merged landing, the footprint used for the slab opening, the quantities.
Spiral stairs
Section titled “Spiral stairs”Set Shape to Spiral in the stair settings — double-click the Stair button — and the same button draws a spiral instead. You get one monolithic body with a helical soffit, not a stack of separate treads.
Plugins → Archeform → Tools → Spiral Stair starts one directly, whatever the switch is set to.
- Click the centre — the axis of the stair.
- Click the start of the first tread. The distance sets the outer radius, the direction sets where the stair begins.
- Move the mouse to sweep it round, and click to build.
| Type a number + Enter | rotation in degrees |
| Shift | lock the rotation to 45° steps |
| ← / → | direction of travel — clockwise or anticlockwise |
| ↑ / ↓ | one riser more or less |
| Esc | step back |
The rotation is unwrapped as you move, so more than a full turn is just a longer drag — 450° is not a special case.
Tread depth is measured on the walk line, 300 mm in from the outer edge by default, as ČSN 73 4130 has it. That is also where the 2h + b check is taken. The dialog warns when the geometry drifts out of range — too shallow at the walk line, or too narrow at the inner edge.
Inner radius is the eye of the stair: the radius of the central column, or zero to run the treads all the way to the axis.
The total rise comes from your storeys. If the stair starts on a storey and there is one above within tolerance, that height is used automatically; otherwise it falls back to 3 m.
Riser height is always derived — total rise divided by the number of risers — so it is never a number you type and never drifts.
The dialog shows a live 2h + b figure. Between 600 and 660 mm is the comfortable range; outside it the indicator warns.
Parameters
Section titled “Parameters”| Field | Default | What it does |
|---|---|---|
| Width | 1 000 mm | clear width of the flight |
| Tread | 280 mm | going, fixed — riser follows |
| Waist | 150 mm | thickness of the slab under the treads |
| Justify | Center | which side the walking line runs on |
| Flight gap | 0 | stairwell between flights of a U |
Changing the width or tread afterwards does not break the geometry — the baseline recomputes its corners from the riser counts.
A spiral uses the same rise, waist and riser count, but its own geometry:
| Field | Default | What it does |
|---|---|---|
| Outer radius | 1 000 mm | to the outer edge of the treads |
| Inner radius | 100 mm | the eye — central column, or 0 for treads to the axis |
| Rotation | 360° | total angle swept; 270, 360 and 450 are the usual ones |
| Direction | Anticlockwise | which way it climbs, seen from above |
| Walk line offset | 300 mm | measured in from the outer edge |
The opening above
Section titled “The opening above”Select the stair, right-click, Archeform → Cut Slab Opening Above.
Archeform finds the nearest slab above the top landing, works out the footprint — including the merged landing of a U — and offers to cut it. Confirm and you get an ordinary slab opening that you can move or resize.
It is a one-off action. Move the stair substantially and cut it again.
Editing
Section titled “Editing”Right-click → Stair Properties. Move and copy use SketchUp’s own commands; copies get fresh identities automatically.
Changing the number of risers moves the difference into the last flight, keeping at least two there.
In IFC and in drawings
Section titled “In IFC and in drawings”Exports as IfcStair — one object, not decomposed into flights — with
Qto_StairFlightBaseQuantities and Pset_StairCommon. Riser and tread counts,
riser height and tread length are filled in from the geometry. The
PredefinedType follows the shape: straight run, quarter turn, half turn, and
SPIRAL_STAIR for a spiral.
In plan the 3D body is hidden and replaced by a clean symbol: tread lines, a break line where the cut plane crosses, the part above the cut drawn dash-dot, and the walking line with a circle at the bottom and an arrow up.
A spiral is drawn the same way, in arcs: the outer and inner edge, a radial line per tread, the break line across the flight, and the walk line as an arc.