Choose dimensions before you write
Settle the grid, the core section and the tenancy depth first, then write the spaces. Do it the other way round and check will pass something that is not a building.
This page is not koyu semantics. The numbers below are design knowledge, taken from real product catalogues and from Japanese design practice. They are not rules of the notation and not guarantees of the implementation. koyu check protects consistency and says nothing about whether a dimension is realistic — a 2m-wide lift and a 30m-deep tenancy both come out green. If you design against a different set of conventions, replace this whole table.
The order
- Pick the grid. For offices and retail, 8,400 is the default.
- Lay out the core section. Read it as three bands: shaft 2,400 + service zone 1,800 + lift lobby 4,200.
- Settle the tenancy depth. Core to window, 8.4–12.6m.
- Settle the storey height. A typical office floor is 4,200 = ceiling 2,800 + service void 1,400.
- Only now write
space.
Structural grid
| Item | Value | Why |
|---|---|---|
| Basic bay, office and retail | 8,400 | the modal bay in large Japanese offices (the middle of 6.4–9.6m); also divides into three 2,800 parking bays |
| Long span (banqueting, column-free) | 16,800–25,200 | two or three basic bays keeps the beam depth realistic |
| Column size | 1,000 low, tapering to 700 square high | narrowed as the building rises |
The bundled examples/twin/ sits entirely on an 8,400 grid.
Vertical circulation
| Item | Value | Why |
|---|---|---|
| 1600kg lift car | 2,150W × 1,600D | the standard size of a real passenger machine |
| Its shaft, one car | 2,800W × 2,400D | car + counterweight + structural tolerance |
| Three side by side = 8,400 = one bay | 2,800 × 3 | the traffic calculation lands straight on the grid |
| Lift lobby, facing banks | 4,200 wide | a single bank wants 2,700–3,500 |
| Service band behind the shafts | 1,800 | holds the electrical, plumbing and duct risers |
| Rule of thumb for car count | office 3,000–4,000 m²/car, hotel 100 rooms/car | starting values for traffic analysis |
| Escalator | 1,200 wide; length ≈ storey height × √3 (12,000 for a 6,900 storey) | 30° pitch; add 2,000 at each landing |
| Vehicle ramp | 6,000 wide for two-way, up to 1:6 | a 4,200 rise wants 25,200 of run — three bays |
Write one shaft per car, one car per space. Bundle them and the plan loses what a lift room actually is.
The size of the stair enclosure decides the step
You do not write riser counts or treads. You write the size of the enclosure, and koyu runs derives the step from it. The tread is derived towards a target of 300mm, and the landing absorbs whatever is left over. Too short an enclosure never reaches the target, and the tread starves.
For a 4,200 rise in a 2,800-wide return stair, varying only the depth in the direction of climb:
4000 L1→L2 stair S rise 4200mm return 24 risers of 175mm, tread 164mm going 3600mm /L1/s
4600 L1→L2 stair S rise 4200mm return 24 risers of 175mm, tread 218mm going 4800mm /L1/s
5000 L1→L2 stair S rise 4200mm return 24 risers of 175mm, tread 255mm going 5600mm /L1/s
5600 L1→L2 stair S rise 4200mm return 24 risers of 175mm, tread 300mm going 6600mm /L1/s
6000 L1→L2 stair S rise 4200mm return 24 risers of 175mm, tread 300mm going 6600mm /L1/s
7000 L1→L2 stair S rise 4200mm return 24 risers of 175mm, tread 300mm going 6600mm /L1/skoyu validate flags a cramped step as stair.proportion (a caution). Of those six, 4,000 and 4,600 are caught; 5,000 and above pass.
⚠ [stair.proportion] s4000.muro:line 11: Derived step dimensions are cramped: 24 risers of 175mm, tread 164mm (2*riser+tread = 514mm; expected 550-700mm)
⚠ [stair.proportion] s4600.muro:line 11: Derived step dimensions are cramped: 24 risers of 175mm, tread 218mm (2*riser+tread = 568mm; expected 550-700mm)A taller storey needs a deeper enclosure. Keep the width at 2,800 and raise the storey to 6,900 — a ground-floor entrance — and 7,000 of depth is what it takes to reach a 253mm tread.
L1→L2 stair S rise 6900mm return 39 risers of 177mm, tread 253mm going 9600mm /L1/s2,800 × 7,000 is the workable block for a protected escape stair — the stairs in examples/twin/core.muro are written at exactly that size.
Section (storey heights)
| Item | Storey height | Made of |
|---|---|---|
| Typical office floor | 4,200 | ceiling 2,800 + service void 1,400 (write slab:1400) |
| Retail | 4,800–6,900 | ceiling from 3,000; the ground-floor entrance at 6,900 (ceiling 6,000) |
| Hotel room, dwelling | 3,200–4,200 | keep 4,200 if it shares a slab with offices |
| Plant floor | 4,600–6,000 | the installation height of the machinery. It does not appear in the storey numbering the public sees — name them M1, M2 |
| Basement car park | 3,300 (2,300+ under the beams) | slab:900 |
koyu levels prints the stack of storey heights as a section. If ceiling plus the slab above exceeds the storey height, check stops you.
Grain of the plan
| Item | Value | Why |
|---|---|---|
| Office tenancy depth, core to window | 8.4–12.6m | standard is 9–13m; past 18m both the workplace and the structure fall apart |
| Hotel room | 4,200 wide × 8,400 deep ≈ 35 m² | width = half a bay divides cleanly |
| Apartment | 8,400 wide (one bay) × 10–12m deep | a 70–90 m² family unit |
| Double-loaded corridor | 2,400 | 2,400–4,200 inside an office core |
| Retail mall | 8,400 wide including the void | walking zone on both sides plus dwell space |
| Toilet block | half a bay (4,200 × 8,400); one bay for both sexes | standard on a typical office floor |
Deep floor plates fail on daylight
One-seventh is a ratio of areas, so past a certain depth no amount of glazing reaches it. Put a single 5,600 × 2,600 curtain wall panel into an 8,400-wide plate and vary only the depth — 10.2m and 16.8m — then run koyu light:
✔ /L1/shallow Depth-10200 window 14.56 m2 / floor 85.68 m2 = 1/5.9 (needs 1/7 ≈ 12.24 m2)
✖ /L1/deep Depth-16800 window 14.56 m2 / floor 141.12 m2 = 1/9.7 (needs 1/7 ≈ 20.16 m2)
✖ Short of 1/7: 1 of 2 rooms (this is a validation judgement)Do the window arithmetic before you commit to the unit layout. A zone that cannot make it is a candidate for a lounge or a store rather than a dwelling. The procedure is in Open windows and pass the daylight check.
Envelope
| Item | Value |
|---|---|
| Curtain wall | one bay wide (8,400) × full storey height as a window says "that face is glass" |
| Grand entrance | two four-leaf automatic doors = 7,200 × 5,000 |
| Dwelling sliding door | 5,600 × 2,600 with sill:200 |
| Parapet and balustrade | h:1200 with air:1 — the edge of a terrace or roof garden |
The edge carrying air:1 is what makes the space semi-outdoor. The daylight coefficient and the outdoor test both follow from it.
What the rentable ratio really is
- A single-use office typical floor runs 70–80% rentable. Across the whole building it falls to 60–70% — the ground-floor lobby and the plant floors eat it.
- A large mixed-use scheme falls further. The bundled
examples/twin/measures as follows: against 141,448.56 m² of floor area, rentable plus exclusive is 46.8%, and 52.2% of the above-ground part once the car park is set aside.
$ npx tsx src/cli.ts stats examples/twin/main.muro
Total 141448.56 m2 (indoor floor area)
Outdoor 24911.04 m2 (plazas, open ground and the like — not counted as floor area)
Semi-outdoor 6534.08 m2 (balconies, external stairs and the like — whether they count is a matter of regulatory detail, so it is reported separately)
By use: common 60487.47 m2 (42.8%) / parking 14868.00 m2 (10.5%) / rentable 63462.21 m2 (44.9%) / exclusive 2630.88 m2 (1.9%)That is an honest number with two cores, two plant floors, a hall, banqueting and planted roof terraces all piled into common.
$ npx tsx src/cli.ts site examples/twin/main.muro
Site /site (敷地)
Site shape: polygon with 14 vertices (a polygon declaration — given geometry)
Site area: declared 23167.40 m2 / derived 23167.40 m2
Road: /road-s (南側道路) width 25000mm / frontage 168000mm
Road: /road-e (東側道路) width 18000mm / frontage 151200mm
Road: /road-n (北側道路) width 16000mm / frontage 168000mm
Building footprint (horizontal projection, rough): 9596.16 m2 → building coverage ratio 41.4%
Total floor area: 141448.56 m2 → floor area ratio 610.5%To raise the rentable ratio, narrow the core — do not deepen the plate. Depth only adds floor without a window.
Next
- Connect storeys — placing stairs and shafts at the sizes you chose
- Open windows and pass the daylight check — the window arithmetic
- Write a typical floor once — writing the floor you just sized, once