1. Zoning categories (13 types)
Every plot inside a city-planning area falls into a zone that dictates allowable uses. Eight residential, two commercial, three industrial. Category I low-rise residential caps height at 10–12 m and severely restricts shops or offices.
2. Building coverage
Ratio of building footprint to lot area. Typical: 30–60% in residential, 80% in commercial zones. Corner plots and fire-zone bonuses can add +10%.
3. Floor area ratio (FAR)
Ratio of total floor area to lot area. From 100–200% in low-rise residential, up to 1,300% in central commercial. A frontage road under 4 m automatically reduces your effective FAR.
4. Sloped-line setbacks
- Road setback line: 1:1.25 slope from opposite road boundary
- Side-boundary line: 1:1.25 above 20 m height
- North-side line: applies in low-rise residential zones, protecting neighbours' sunlight
Most "we couldn't fit a third floor" stories trace back to this rule.
5. Absolute height limit
In Category I and II low-rise residential, height is capped at 10 m or 12 m. Designers either go underground or sneak space into the roof.
6. Fire and quasi-fire zones
Common in urban Osaka and Tokyo. Wood houses must meet fire-rated envelopes, soffits, and openings — adds 5–10% to cost.
7. Road frontage rule
A buildable lot must front a public road of at least 4 m width for at least 2 m. Lots that fail this rule are "no-rebuild" and unbuildable.
The scale of your home is not set by the size of the land — it is set by zoning × coverage × FAR × sloped-line. Always run an architect's volume check before signing the land contract.