1. Maximizing zoning and floor-area ratio
Commercial zones allow 400–1300% FAR; neighborhood commercial 200–400%. Using corner-lot rules, street setback lines and sky-factor, a larger building than the nominal FAR can sometimes be built. An architect's volume study shifts the outcome by ±20%. Project viability is largely decided in this early stage.
2. Choosing the structure
- Steel: ideal for 5–10 storeys, short schedule, column-free large spaces
- SRC: 10–20 storeys, high rigidity, little dead space
- CFT: over 20 storeys, slimmer columns, suited to Grade-A class
3. Optimizing the rentable ratio
Rentable ratio = leasable area ÷ gross floor area. A standard office building is 70–80%. Consolidating the core (elevator hall, stairs, toilets) at the center maximizes leasable area. A 1% difference becomes tens of millions of yen in revenue over ten years.
4. Standard systems
| Floor | OA raised floor (H100–150mm) standard |
| Ceiling | System ceiling, H2,700mm+ recommended |
| HVAC | Individual or central + zone control |
| Elevators | 1 per 2,000–3,000㎡ (Tokyo basis) |
| Electrical | 30VA/㎡+, emergency power 72h+ |
5. Regulations and mandatory provisions
Mandatory parking (1 to dozens of spaces by site area), bicycle parking, greening, welfare facilities, fire stairs. These trim building volume by 5–10%. Fail to fold them in early and the effective area shrinks later.
6. Schedule and budget
- 5 storeys: 15–18 mo / ¥1.2–1.8M per tsubo
- 10 storeys: 24–30 mo / ¥1.5–2.2M per tsubo
- 20 storeys: 30–42 mo / ¥2.0–3.0M per tsubo
7. The performance tenants demand
Rent is not driven by location alone. Ceiling height, column-free span, floor loading, electrical capacity and telecom infrastructure shape which industries prefer a building. IT and finance want high electrical capacity and raised floors; professional and service firms want easily divisible typical floors. The harder a performance is to change after completion, the more headroom you should build in at design.
8. Spec comparison by grade
"Standard" and "Grade A (high-grade)" offices demand very different specs. The table shows guide figures for representative indicators.
| Item | Standard | Grade A |
|---|---|---|
| Ceiling height | 2,600–2,700mm | 2,800mm+ |
| Column-free span | columned grid | large column-free span |
| Electrical capacity | 30–50VA/㎡ | 60VA/㎡+ |
| Emergency power | 72 hours | 72h + BCP-ready |
| Environmental cert. | optional | designed to certify |
9. BCP, energy efficiency and green certification
Business continuity (BCP) and energy performance have become key axes in tenant selection. Beyond emergency generation, water supply and flood measures, designs that curb running cost with insulation, high-efficiency HVAC and LED are valued. Meeting environmental certifications ties directly to attracting prime tenants and sustaining rent. The upfront cost is real, but it underpins long-term competitiveness as an income property.
An office building is "income real estate." The quality of the design ties directly to the post-completion rent—¥3,000–10,000 per ㎡ of difference.