Daylight — daylight.ratio / daylight.unknown

rule	level
daylight.ratio	violation
daylight.unknown	caution

The scope of the daylight question is declared, never inferred. A room is not necessarily a habitable room, and a storage may well be required to have a window. The one-seventh judgement applies to the spaces you wrote daylight:1 on, and nowhere else. At what grain the question is asked — a whole dwelling, or each room it is divided into — is decided by where you write daylight:1.

The only values daylight: accepts are 1 (in scope) and 0 (out of scope). Write daylight:yes and koyu check makes it an error on the spot — a value it cannot interpret must not fall silently back to a default, taking the judgement with it.

The numbers, and where the threshold enters

Floor area and effective window area are numbers, not judgements. koyu light returns those numbers; this volume applies the threshold.

• Floor area — the area of the region, measured to wall centrelines (m²).
• Effective window area — for every window written on a boundary of that space, w × h × factor, summed (m²).
• Required area — floor area ÷ 7.

The factor depends on what the window faces. That is a derivation of form, not an architectural judgement.

what the window faces	factor
an exterior space (exterior)	1.0
a semi-outdoor space with a floor above it — under an eave or an upper balcony	0.7
a semi-outdoor space open to the sky — a garden, a top-floor balcony	1.0
an indoor neighbour	0 (not counted)

Being semi-outdoor is derived too: a space that meets an exterior across a type:open boundary, or across an air:1 boundary (a railing or anything else that does not screen), is semi-outdoor. "Has a floor above" means some space on any level overlaps it from above.

The judgement is coarse. No correction factor is applied, no use-based proportions are considered, and no distinction is drawn between buildings the rule applies to and those it does not. It is an early warning at the resolution of a scheme design, not a compliance verdict.

daylight.ratio — insufficient daylight

violation

The effective window area is below one seventh of the floor area.

koyu 1.0
grid X 0 3600
grid Y 0 4500
level L1 0 h:2400 slab:150
space /out exterior
space /L1/a room X1..X2 Y1..Y2 daylight:1
boundary /L1/a /out t:150
  window w:600 h:600 edge:S
  door w:900 edge:N

✖ [daylight.ratio] main.muro:line 6: Insufficient daylight: /L1/a — effective window 0.36 m2 < required 2.31 m2 (1/7 of the 16.20 m2 floor)
Validation — 1 violation / 0 cautions

A 600×600 window is 0.36 m²; the floor is 3600×4500 = 16.20 m², so 2.31 m² is required. It is short by an order of magnitude.

Fix — enlarge the windows or add more. Check that h: has not been forgotten (if it has, the daylight.unknown below will be there too). If the space does not need the question asked of it, drop daylight:1.

koyu light lays the numbers out room by room so you can see how far short you are.

Under a balcony the factor is 0.7

The same window through a balcony with a floor above it is multiplied by 0.7.

koyu 1.0
grid X 0 3600 5400
grid Y 0 4500
level L1 0 h:2400 slab:150
level L2 2550 h:2400 slab:150
space /out exterior
space /L1/a room X1..X2 Y1..Y2 daylight:1
space /L1/b balcony X2..X3 Y1..Y2
space /L2/a room X2..X3 Y1..Y2
boundary /L1/b /out type:open
boundary /L1/a /L1/b t:150
  window w:2400 h:1200
boundary /L1/a /out t:150
  door w:900 edge:N
boundary /L2/a /out t:150
  door w:900 edge:N

✖ [daylight.ratio] main.muro:line 7: Insufficient daylight: /L1/a — effective window 2.02 m2 < required 2.31 m2 (1/7 of the 16.20 m2 floor)
Validation — 1 violation / 0 cautions

The window is 2400×1200 = 2.88 m², but /L2/a sits on top of the balcony, so 2.88 × 0.7 = 2.02 m², short of the 2.31 m² required. Remove /L2/a and the same window counts as 2.88 m² and the judgement passes — what sits above the balcony decides the daylight of the room below it.

daylight.unknown — the window area is not fully counted

caution

A window without h: has dropped out of the sum.

koyu 1.0
grid X 0 3600
grid Y 0 4500
level L1 0 h:2400 slab:150
space /out exterior
space /L1/a room X1..X2 Y1..Y2 daylight:1
boundary /L1/a /out t:150
  window w:2400 h:1200 edge:S
  window w:600 edge:E
  door w:900 edge:N

⚠ [daylight.unknown] main.muro:line 6: Window area is not fully counted: /L1/a has a window without h: (write h: on it)
Validation — 0 violations / 1 caution

A window with no h: has no height, therefore no area, and it falls silently out of the sum. Silence there makes "it is enough" indistinguishable from "it was not counted." This caution exists solely to keep those two apart.

Here the south window alone (2.88 m²) already clears one seventh, so no daylight.ratio appears. Both can appear together, and if every window lacks h: the effective area is 0.00 m² and daylight.ratio comes with it.

Only windows on boundaries whose factor is not zero are counted. A window facing an indoor neighbour without h: says nothing, because it was never going to be counted.

Fix — write h: on that window. If it has nothing to do with daylight (an inspection hatch in a cupboard, say), drop daylight:1 from the space instead.

See also

• koyu light — the floor and effective window areas themselves
• The validation ledger — all fifteen rules, and why Finding is not Diagnostic