How to plan a ladder / space-saver stair.
A ladder stair is a steep, compact secondary stair for places where a normal stair simply doesn't fit — lofts, mezzanines, attics, sheds, plant rooms, guest galleries. The treads can overlap in plan view to shrink the horizontal footprint to a third of a regular run, at the cost of a steeper, slower climb.
When is a ladder stair the right choice?
Use a ladder stair when you have less than roughly 1.5 m of clear horizontal length for the climb — typical loft conversions, gallery beds, attic access, plant-room ladders, technical rooms in tight basements. A normal stair would need 2.5–3 m for the same floor-to-floor; the ladder cuts that to 1.0–1.8 m by allowing the tread boards to overlap in plan view (each tread projects back under the next one). The trade-off is steeper slope and slower walking. If you have the room for a regular stair, switch to the straight or L-shapedcalculator — they'll always feel better underfoot.
Where a ladder stair is NOT allowed
A ladder stair counts as a Nebentreppe (secondary stair)in DIN 18065 §6.1 and EN 14076. That means it's only legal where the room it serves is secondary use — not the primary access to a habitable level.
- OK: loft / gallery without a fixed sleeping place, storage attic, plant room, technical floor, garden shed, treehouse.
- NOT OK as the only access:bedroom, child's room, office with daily occupancy, anywhere on an escape route, anywhere with code-mandated accessibility (barrier-free apartments per DIN 18040).
When in doubt, ask your local building authority before you cut wood.
Four numbers to get right before you build
- Slope 55–75°. Below 55° a normal stair fits better; above 75° you need a true ladder (rungs, both hands).
- Rise per step ≈ 180–220 mm. Ladder stairs run steeper than a normal stair (which tops out at 200 mm). Above 240 mm it stops being walkable face-forward — you end up turning sideways or backing down.
- Tread board depth ≥ 180 mm.That's the actual board you stand on. The plan-view step advance can be much smaller (90–120 mm) because the boards overlap in plan — your foot still rests on the full 180 mm of tread material.
- Always one handhold.A wall-mounted grab rail or a side rope is mandatory at this slope — even when it's not required by the local code, plan for it during install.
What "Stair Depth" really means
Unlike the other calculators, where the horizontal footprint is set by step count × tread depth, here you pin it directly with the Stair Depth slider. The step advance is then derived (stairDepth ÷ stepCount), so if you set a tread board depth larger than the advance, the boards overlap in plan view. The Plan overlap tile in the results panel shows you how much each tread projects back under the next one — typically 100–150 mm on a working space-saver.
How to read the live preview
The 3D view shows the stair in context with both closed stringers and the floor opening. The 2D Top view reveals the tread overlap — adjacent tread polygons literally share plan-view pixels. The X-Ray view lets you see the dadoes inside each stringer where every tread is let-in. All three update live as you move a slider on the left.
What you'll get when you export
Five formats, all derived from the same geometry as the preview above:
- PDF · multi-sheet A3 construction drawing. Cover with project summary, plan view, side elevation, scaled workshop drawings for both stringers and every tread (with dado pockets), and a bill of materials. Print at A3 for the workshop; do not use as a 1:1 cutting template.
- DXF · 1:1 CAD/CNC zip. One file per category (plan, elevation, each part) at true 1:1 scale in the chosen unit. Named layers separate stringers, treads, dadoes. Loads straight into AutoCAD, BricsCAD, LibreCAD, and any CNC post-processor.
- SVG · 1:1 vector zip. Same drawings as the DXF, also at true 1:1 scale, in plain SVG — for browsers, Illustrator, Inkscape, Affinity, or SVG-input laser cutters.
- STL · 3D printable mesh. A single solid model for slicing and 3D printing a tabletop reference, or for importing into Blender / Twinmotion / Lumion for renders.
- STEP · parametric CAD exchange. Each tread and each stringer as a separate B-Rep body, with the dado pockets baked in as proper hole loops. Opens natively in SolidWorks, Inventor, Fusion 360, FreeCAD, SolidEdge.
What the files do not include
The downloads are a construction foundation, not a turnkey product. The geometry pipeline is conservative — when in doubt it errs on the side of clear space — so the parts will fit, but final aesthetic millwork (chamfers, edge rounding, anti-slip grooves, plug covers, sanding profiles) is up to whoever builds it. Floor- and ceiling-side connections (foot anchor, top-edge fastening into the upper-floor joist) are not modelled and must be detailed on site by your carpenter. Always verify every dimension on site before cutting wood.