What happens when you write nothing

Writing nothing means something. And it means one of three things.

Kind of silence	What happens	Example
A default applies	a fixed value or a fixed rule stands in for what was not written	a boundary with no type: is a wall
Nothing is generated	no value is invented, and the element is simply not made. The shape is still determinate, just thinner	a level with no slab: gets no floor at all (SUF03, a warning)
It stops	information needed for a single determinate shape is missing	with no ceiling height anywhere, SUF01, an error

No default is ever invented in order to press on. That is why the same description always yields the same shape — and why a shape that came out thin is always reported.

This page is the one table of defaults. How values are written is in the three tiers of attribute, how positions are spelled in positions and regions, and the compass defaults in orientation and the a side.

The smallest file

koyu 1.0
grid X 0 3600
grid Y 0 4000
level L1 0 h:2400 slab:150
space /L1/a room X1..X2 Y1..Y2

Five lines on which check is green and a plan is drawn. Everything else is a default — no name, no exterior, not one boundary declared.

Foundation declarations

Written nothing	What happens
koyu <version>	read under the newest version, 1.0. Write it to pin the meaning → the version line
unit mm	mm. v0 has no other unit
name	the building has no name
grid X / grid Y	no grid reference can be written at all. Any line with a region stops with Undefined grid line name
level	a space with a region has no determinable level — SUF02 (error)
h: on a level	unless the space carries its own h:, the ceiling height is undetermined — SUF01 (error). Neither ceiling nor roof can be generated
slab: on a level	not one floor is generated on that storey. SUF03 (a warning) — the shape is determinate, so it does not stop
underground: on a level	treated as above ground. It is never inferred from a negative z
pitch: on a level	required on a range declaration (L4..L10); it cannot be written on a single level

space

Written nothing	What happens
a region	the space has no region. It appears in no area, carries no column and no floor — which is exactly right for an exterior or an aggregation-only space
level:	the first path segment, if it names a level. If it does not match, SUF02 (error)
h:	the level's h:. With neither, SUF01 (error)
daylight:	out of scope for the daylight question. It is never inferred from the type — neither room nor ldk puts a space in scope
ceiling:	a ceiling is derived as the outline of the room × its ceiling height. ceiling:0 builds none
use:	inherited from the deepest zone ancestor. With none there either, the space has no axis of aggregation
road:	not a road. It contributes no width to frontage
uid:	the path is the identity. Rename it and the correspondence is cut
stair: ramp: escalator: lift:	not a vertical circulation. Just a space
floor: spec:	there is simply no value to carry

boundary

The default between touching spaces is a wall.

Written nothing	What happens
a boundary for a touching pair on one level	a wall boundary is derived. It carries no door, so it cannot be passed. It does not appear in the machine format
a vertical boundary between stacked spaces	it is a floor. It cannot be passed. stair / shaft / void are the exceptions, and they are declared
a boundary with a space that has no region (an exterior)	nothing is derived. There is no wall there, and the envelope has a hole — koyu validate says so as envelope.gap
type:	wall
t:	100 mm for drawing and for solids. An air:1 boundary defaults to 60 mm, capped at 80 mm
air:	treated as a thing that blocks
edge:	all of that boundary's segments. To place an opening or a seg, the face must resolve to one, or OPN05 / SEG05
h: (on air:1)	a top at 1100 mm
spec: fire: sound:	there is simply no value to carry

One declaration on the pair suppresses the derived wall. That holds even if the declaration named a single face with edge: — the remaining faces get no derived wall either.

door / window

Written nothing	What happens
w:	an error. Width is required (the asset may supply it)
at:	the ratio 0.5 — the middle of the segment. Clamped to fit
hinge:	the start end of the segment (west on a horizontal one, south on a vertical one). Pinned to the start on a diagonal
swing:	opens toward a if a has a region, otherwise toward b
style:	hinged
h: on a door	it rises from the floor to a head height of 2000 mm
h: on anything else	1200 mm tall, with its head at 2000 mm
name:	it has no name. Composition can no longer point at it — there is nothing for = window W1 to find
any door at all	it cannot be passed. check stays green

A sill height follows without writing sill: — it falls out of aligning the heads. sill: is carried, so writing it changes no shape.

column

Written nothing	What happens
d:	the same as the size (a square column)
x: / y:	every grid line. One stands at every intersection with floor on that level
name:	drop column can no longer point at it

Two columns never stand at one intersection — the earlier declaration wins.

Vertical circulation

Riser count, tread and slope are never written. What is written is the region and the direction; the rest follows from the storey height.

Written nothing	Default
form:	straight (it does not turn back)
turn:	R (turning right at the landing)
entry:	a boarding floor 1100 mm deep
riser:	a maximum riser of 180 mm — the number of steps follows from it
tread:	a target tread of 300 mm — used when the landing is taken as the remainder
landing:	derived (a minimum of 1100 mm). Write it and the tread becomes the remainder instead
lane:	1200 mm per escalator unit — the number of units follows from it
slope:	no permitted slope was declared, so the slope is not faulted. Only escalators are checked against the usual range, by run.slope

zone / polygon / band

Written nothing	What happens
site: on a zone	it is not a site aggregation and koyu site ignores it
area: on a zone	there is no surveyed figure to reconcile the derived area against
polygon	the site area is derived from the union of the spaces on the site and the indoor footprint. No site boundary line is drawn
w:rest in a band	the band is closed. The member widths must sum to the extent of the band, or the file stops — the same arithmetic as "part dimensions add up to the overall dimension" on a drawing

Constants of derivation

These are not ledger defaults. The ledger says what may be written; this table says what is derived when nothing was. What you write always wins.

Constant	Value	What it decides
Wall thickness	100 mm	a wall with no t:. Split half to each side of the centreline
Non-blocking boundary thickness	60 mm	the t: default on air:1
— its cap	80 mm	whatever t: says, it stops here
— its top height	1100 mm	the h: default on air:1
Head height	2000 mm	doors rise to it; everything else hangs down from it
Height of a non-door opening	1200 mm	the h: default
Ceiling face thickness	30 mm
Roof slab thickness	200 mm	also how far above the ceiling height the top storey is capped
Plan cut plane	FL + 1200 mm	the height at which a plan is cut
Maximum riser	180 mm	the riser: default
Target tread	300 mm	the tread: default
Minimum intermediate landing	1100 mm	a written landing: is raised to it
Boarding floor depth	1100 mm	the entry: default
Nominal escalator width	1200 mm	the lane: default
Step face thickness	200 mm	solids
Landing and inclined slab thickness	200 mm
Escalator step pitch in plan	400 mm

Green does not mean "it stands up as a building"

Because the default between touching spaces is a wall, a two-storey building with no door declared anywhere is completely sealed — and green.

koyu 1.0
grid X 0 3600
grid Y 0 4000
level L1 0 h:2400 slab:150
level L2 2900 h:2400 slab:150
space /L1/a room X1..X2 Y1..Y2
space /L2/a room X1..X2 Y1..Y2
space /out exterior
boundary /L1/a /out t:150
boundary /L2/a /out t:150

✔ Consistent — 3 spaces / 2 boundaries
  Structural consistency only — architectural validity is what koyu validate says, separately

Saying that it has no door is a different face (the location prefix is the resolved absolute path; it is elided below).

✖ [access.unreachable] …/sealed.muro:line 6: Cannot reach the exterior: /L1/a (no passable boundary leads out — write a door)
✖ [access.unreachable] …/sealed.muro:line 7: Cannot reach the exterior: /L2/a (no passable boundary leads out — write a door)
Validation — 2 violations / 0 cautions

What check says goes exactly as far as "what was written does not contradict itself as data". Never claim it works on the strength of green.