Stairs: every shape, and stairs that start or land off a floor

The Stair tool draws a stair from the story you are on up to the next one. The first click is the centre of the first riser (the front of the bottom step), the second click gives the walking direction; Shift keeps it to 45° steps, or type an angle and press Enter.

The height comes from the stories: FL of 1F to FL of 2F, here 2,850 — the riser count is chosen so that each riser stays near 190.

The new stair is selected and the Info Box shows its main numbers: Shape, Width (有効幅), Height · linked to story (it follows if you change the story heights), Risers × rise (蹴上), Going (踏面) and 2R + G — the comfort rule (600–650 is easy to walk). The rise turns red in the Info Box as soon as it goes over the legal maximum.

Drag the left edge of the panel to give it room. Under the previews, Building Standards Act, Order Art. 23/25 (houses) checks the stair live, with the house limits of 令23条: riser (蹴上) ≤ 230, going (踏面) ≥ 150, clear width ≥ 750, plus 令24条 (a landing every 4 m of rise) and 令25条 (a handrail). Here: OK for a house: rise 190.0 ≤ 230, going 240 ≥ 150, width 780 ≥ 750.

The width the law means is the clear width between handrails; a handrail that sticks out 100 mm or less is not deducted (令23条3項).

Each change is one undo step and the check updates at once: ⚠ Riser 237.5 mm > 230 mm (蹴上げ, 令23条). Auto fit sets the risers so that each is 200 or less and the going so that 2R + G = 630 — the stair gets longer, the side view shows it. With the handrail side on None the check says No handrail on either side (手すり, 令25条); a railing drawn on the stair with the Railing tool also counts (part 4).

The same check runs for every stair in Structure › Law checks and the AI assistant's law_checks.

A stair with a landing is a list of flights (段): each has its risers, its going and width (or the stair's), the turn after it (straight on, left 90°, right 90°, U left, U right) and the landing (its length, or 回り = winders). + Flight splits the last flight and adds a landing. The landing sits on a whole riser — its height above FL is shown, and you can type it (part 3).

令24条: a house stair needs a landing for every 4 m of rise; a straight landing must then be 1.2 m deep or more — the check says so if not.

A U stair turns 180° on its landing; Risers before the turn moves the landing up or down. Flip › Turn side makes it turn the other way, Direction makes it walk the other way (it then starts where it arrived). The plan preview and the side view follow every change.

Winders save the landing's space but the narrow end of each step is short. The law measures their going on the walking line 300 mm from the narrow side (令23条2項); the check gives that figure after the OK (winders 155 at 300). 3 × 30° is the usual Japanese pattern; 2 × 45° gives deeper winders (230 at 300) but steeper corners. A Landing (踊場) instead of winders is the safer choice for elderly residents.

A preset only fills the flights table: pick one, then change any flight. Custom keeps the table as you made it — any number of flights, each turning left, right or back, with flat landings or winders, and its own going and width. The same shapes are in the Info Box's Shape list.

A mezzanine is a slab of the story with a level above its FL (Floor | Mezzanine 中2階, Level FL+). Design › Mezzanine… starts the Slab tool with that preset: draw the outline, or Space+click in a room. Room on it adds a room at the mezzanine level (its own area and ceiling height), and Railing On puts a railing on its open edges.

Draw a stair in B1, starting 1,380 before the mezzanine edge and walking towards it. As drawn it still rises to 2F (15 risers, far too long). Open its settings.

Arrives at lists the mezzanine slabs of the story. A stair that arrives on a mezzanine keeps its height linked: raise the mezzanine (Level FL+) and the stair follows. It cuts no stair hole in the floor above — it does not go through it — and the mezzanine railing (Railing On) leaves a gap where the stair arrives.

A half flight like this is the usual split-level スキップフロア: 7 risers of 200 between two levels of the same story.

A loft is a mezzanine slab on the top story. Under the 2,800 ceiling, a loft at FL+1,400 leaves 1,400 above it — the height under which a 小屋裏物置等 (ロフト) is not counted as a story or as floor area, if its area is under half of the floor below (平12建告1351). Whether a fixed stair to a loft is allowed depends on the 特定行政庁: check before you draw one; a ladder is the alternative.

The total stays (15 risers of 190); a landing always sits on a whole riser, so the height you type is rounded to the nearest one (7 × 190 = 1,330). Use it to land on a platform that meets a door, a window sill or a split-level floor half-way, and give the landing its own length in the row under it.

An outdoor stair is an ordinary stair of the lower story drawn outside the walls; it rises from that story's FL to the FL of the story above, where the deck (or a balcony from the Balcony / terrace tool) is. Give it handrails on both sides — an outdoor stair is often a 屋外階段 with its own rules (width, the fire route of a 共同住宅); for a house the 令23条 limits above apply. The structure of the deck (piers, beams, joists) is laid by the Deck tool.

The hole is the stair's footprint plus its stringers, cut from the slabs of the story above; Stair hole (階段開口) in Stair settings turns it off (a stair in a 吹抜) or adds a clearance around it. It follows the stair when you move or reshape it.

Floor area 床面積: the opening of a stair is not a 吹抜 — under 令2条1項3号 the stair counts on every floor it passes, so the 2F floor area keeps the opening (only a bigger void beyond the stair is left out). The headroom over the stair is yours to check in a section (part 4).

The stair's own handrail (Stair settings › Handrail: side, height above the nosing 750–850, profile, wall brackets or posts with balusters) is the handrail 令25条 asks for. The Railing tool adds a full balustrade (手摺子, gap ≤ 100 between balusters) on an open side; in Polyline mode it draws the railing along a mezzanine, a balcony or a stair hole (a guard of 1,100 or more where you can fall: 令126条 for balconies).

Stair settings › Treads, risers and stringers: nosing (段鼻), tread thickness (踏板), closed or open risers (蹴込み), the stringer type — side boards (側桁), cut stringers (ささら桁) or a centre beam (力桁) — and its thickness; Materials gives each part its own material (treads, risers, stringers, handrail). The 3D, the sections and the quantities use the same parts.

Every section and elevation draws the stairs from the same model: treads and stringers in cut where the line crosses them, the rest in view, with the landing, the mezzanine, the floor above and its hole. Use it to check the headroom over the stair (2,000 or more is the usual target; the law sets none for houses) — and click a stair in the section to select and edit it.

The floor framing lays the beams and joists of the floor and frames every opening: a header 受け材 across each end of the hole the joists frame into, and a trimmer along each side, so no joist end is left open. The beam check (Structure › Bracing & structure checks › Beams) then checks the headers with the load of the joists they carry.

The plan symbol follows the Japanese convention: on the story where the stair starts, the treads up to the cut height (Stair settings › Plan cut height, 1,800) are drawn solid with the arrow UP (上 with Japanese drawing labels), a break line, and dashed treads above it; on the story above, the whole stair with DN (下). Winders, landings and the handrail line are drawn too, and the permit plans 平面図 use the same symbol.

Every stair is counted from its geometry: the number of treads and risers with their size, the stringers, the handrail and railings in metres, and the stair as a fitting. Prices come from your Price list… — the estimate never invents one. That is the whole stair workflow: draw, check the law, shape it, land it where it must go, detail it, draw it and count it.