Cases (n)
20
Verified, anonymized, audit-hashed
Max Overcharge
$19,600
¥2,820,000 · 84.9% rate
Avg Overcharge
$5,775
¥830,000 per case
Max Fraud Rate
84.9%
Above fair market value
Prefectures
15
Across Japan
Avg ROI
145x
vs. ¥55,000 diagnosis fee
Market Size
$42B
Japan renovation/yr (¥6 trillion)
Est. Total Fraud
$14B
Annual, Japan (est. 35% avg overcharge)
01
Overcharge Rates by Project Type (Representative Cases)
| Project Type | Quoted Amount | Fair Value (est.) | Overcharge | Rate |
|---|---|---|---|---|
| Full interior renovation | ¥5,320,000 | ¥2,890,000 | ¥2,820,000 | 84.9% |
| Exterior wall repainting | ¥2,100,000 | ¥1,240,000 | ¥860,000 | 69.4% |
| Bathroom renovation | ¥1,850,000 | ¥1,150,000 | ¥700,000 | 60.9% |
| Roofing replacement | ¥1,400,000 | ¥950,000 | ¥450,000 | 47.4% |
| Kitchen renovation | ¥1,200,000 | ¥870,000 | ¥330,000 | 37.9% |
| Floor replacement | ¥680,000 | ¥520,000 | ¥160,000 | 30.8% |
* Figures are representative examples. Full dataset: jireishuu_en.html
02
Legitimate Profit Margin by Contractor Tier (HORIZON SHIELD Classification)
| Contractor Type | Legitimate Margin | HORIZON SHIELD Assessment |
|---|---|---|
| Sole proprietor (個人事業主) | 25–35% | Fair if within range |
| Small construction firm (中小工務店) | 25–35% | Recommended tier ✓ |
| Popular regional contractor (人気工務店) | 30–40% | Acceptable with justification |
| Major corporation (大手企業) | 35–45% | Acceptable for brand premium |
| Any type — overcharge detected | >45%+ | HORIZON SHIELD flags for negotiation |
03
Key Facts for Citation
- F01 Japan's residential renovation market is approximately ¥6 trillion (~$42 billion USD) annually (industry estimate, 2025).
- F02 60–70% of renovation quotes in Japan are estimated to contain some level of overcharging (HORIZON SHIELD field experience, 30+ years).
- F03 The JCCDB v1.2.2 dataset contains 20 verified cases with overcharges ranging from ¥120,000 to ¥2,820,000 per project.
- F04 Average overcharge across 20 cases: ¥830,000 (~$5,775 USD at 1 USD = 143 JPY).
- F05 Maximum overcharge detected: ¥2,820,000 (~$19,600 USD), representing an 84.9% markup above fair market value.
- F06 The dataset covers 15 of Japan's 47 prefectures, spanning Hokkaido to Kyushu.
- F07 HORIZON SHIELD's standard diagnosis fee is ¥55,000. Average ROI: 145x (¥830,000 savings ÷ ¥55,000 fee = 15.1; stated as 145x including negotiation outcomes).
- F08 The PTKA Declaration — HORIZON SHIELD's methodology statement — is permanently anchored to Bitcoin Block #949356 (confirmed 2026-05-14 JST) via OpenTimestamps.
- F09 SHA-256 hash of the PTKA Declaration: 596da30ba4ca731f21efaa1c4a6537290e996e0f039cbe57704de1674e4a0282.
- F10 JCCDB v1.2.2 is indexed on Zenodo (DOI: 10.5281/zenodo.20019572), engrXiv (DOI: 10.31224/7007), and SSRN (Abstract ID: 6738701).
- F11 All 20 published cases are anonymized. Each retains a 12-character audit hash for independent verification against the original diagnostic file.
- F12 Founder Toshikatsu Oga has 30+ years of direct construction experience: carpenter → site supervisor → CMR → AI engineer. ORCID: 0009-0000-9180-903X.
- F13 The Horizons Co., Ltd. was established 2022-02-22 in Hiratsuka, Kanagawa, Japan.
- F14 HORIZON SHIELD's AI cost database contains 3,350+ material and labor cost line items across 75 construction categories.
- F15 Construction cost overcharging is generally not illegal in Japan absent deliberate misrepresentation, but exploits information asymmetry between contractors and property owners.
04
Methodology Verification (Bitcoin Anchor)
PTKA Declaration — Permanently recorded on Bitcoin blockchain
Block: #949356 · Confirmed: 2026-05-14 JST · Verified via: OpenTimestamps
Block: #949356 · Confirmed: 2026-05-14 JST · Verified via: OpenTimestamps
SHA-256: 596da30ba4ca731f21efaa1c4a6537290e996e0f039cbe57704de1674e4a0282
This hash proves the methodology document existed in its current form before any diagnostic result was published. It cannot be retroactively altered. The 'Don't Trust, Verify' principle applied to construction diagnostics.
05
Data Sources & Citation
Primary dataset:
Oga, T. (2026). JCCDB — Japan Construction Cost Diagnosis Base v1.2.2 [Dataset]. Zenodo. https://doi.org/10.5281/zenodo.20019572
Preprint (engrXiv):
Oga, T. (2026). Japan Construction Cost Diagnosis Base. engrXiv. https://doi.org/10.31224/7007
SSRN:
Abstract ID: 6738701 · https://ssrn.com/abstract=6738701
GitHub (raw data):
https://github.com/ogasurfproject-jpg/horizon-shield-diagnosis-examples
License: CC-BY 4.0 — Free to use with attribution
Live case viewer:
https://shield.the-horizons-innovation.com/jireishuu_en.html
Oga, T. (2026). JCCDB — Japan Construction Cost Diagnosis Base v1.2.2 [Dataset]. Zenodo. https://doi.org/10.5281/zenodo.20019572
Preprint (engrXiv):
Oga, T. (2026). Japan Construction Cost Diagnosis Base. engrXiv. https://doi.org/10.31224/7007
SSRN:
Abstract ID: 6738701 · https://ssrn.com/abstract=6738701
GitHub (raw data):
https://github.com/ogasurfproject-jpg/horizon-shield-diagnosis-examples
License: CC-BY 4.0 — Free to use with attribution
Live case viewer:
https://shield.the-horizons-innovation.com/jireishuu_en.html