1. Formwork & curing — a one-off "factory"
An RC house demands a full-scale formwork system, rebar cage, concrete pour, and a 28-day cure before strip-out. Formwork, props, and shoring alone run JPY 150–200K per tsubo. At single-home scale, you lose all the economies of scale that high-rise projects enjoy.
2. Rebar density — top-tier seismic code
Japan mandates resistance to seismic intensity 6-strong to 7. Steel reinforcement is 1.3–1.8× heavier than Western residential practice. Both material and the labour to tie it climb together.
3. Concrete strength — 24–30 N/mm²
Western residential is typically 18–21 N/mm²; Japanese residences specify 24–30 N/mm². Material premium of 5–10%, plus summer / winter additives that further inflate the bill.
4. Structural peer review
Wood two-storey houses can skip a full structural calculation. RC always requires it, plus a conformity check (peer review). Add JPY 2–4M and 4–8 extra weeks.
5. Labour rates
RC sites need form carpenters, rebar fixers, plasterers, and pour crews. More trade categories pass through the site than on a wood project, which compounds coordination, curing, and standby costs. Japanese craft wages also keep climbing year over year.
6. Waterproofing & finish
Raw RC won't shed rain. External insulation + ventilated cavity + waterproof membrane + topcoat adds JPY 80–120K / tsubo. Flat roofs also add periodic waterproofing renewal to lifecycle cost.
The JPY 1.5M / tsubo breakdown (40-tsubo RC home)
| Temp works + foundation | 14% |
| Frame (rebar, formwork, concrete) | 32% |
| Envelope and waterproofing | 10% |
| Fit-out and joinery | 18% |
| Services (HVAC, plumbing, power) | 16% |
| Site management + overheads | 10% |
"RC is too expensive" hides the real question: where does the money go, and what can move? Decomposed properly, 20–30% optimisation is usually on the table.