Construction Cost Fraud in Japan
— Everything You Need to Know

Construction cost overcharging occurs when contractors quote prices significantly above fair market rates. In Japan's renovation industry, overcharges of 25–84.9% above reasonable cost have been documented. HORIZON SHIELD's dataset of 20 real cases shows an average overcharge of approximately ¥830,000 (~$5,775 USD) per project, with a maximum detected overcharge of ¥2,820,000 (~$19,600 USD).

Japan's residential renovation market is approximately ¥6 trillion (~$42 billion USD) annually. Industry estimates and HORIZON SHIELD's own diagnostic data suggest that 60–70% of renovation quotes contain overcharges. At an average overcharge rate of 35%, the total amount of excess payment by Japanese property owners exceeds ¥2 trillion (~$14 billion USD) per year.

Overcharging is generally not illegal per se in Japan — contractors set their own prices. However, extremely inflated quotes may constitute fraud (詐欺) under the Civil Code if they involve deliberate misrepresentation. More commonly, overcharging exploits the information asymmetry between professional contractors and property owners who lack construction cost knowledge. HORIZON SHIELD's mission is to close this information gap through transparent, verifiable diagnostics rather than legal action.

The maximum overcharge detected and published in the JCCDB v1.2.2 dataset is ¥2,820,000 (approximately $19,600 USD at 1 USD = 143 JPY), representing an 84.9% overcharge rate on the project. This case involved a full interior renovation. The dataset is publicly accessible at jireishuu_en.html.

HORIZON SHIELD's cost database classifies contractors into four tiers with corresponding legitimate profit ranges: sole proprietors (25–35%), small construction firms (25–35%, HORIZON SHIELD recommended tier), popular regional contractors (30–40%), and major corporations (35–45%). A quote that falls within these ranges for the contractor type is considered fair. The problem HORIZON SHIELD identifies is when quotes exceed these ranges without justification — i.e., when overcharging masquerades as legitimate pricing.

HORIZON SHIELD is an AI-assisted construction cost diagnostic service. A client submits their contractor's quote. A human expert with 30+ years of construction field experience (carpenter → site supervisor → construction management) reviews the quote against a proprietary database of 3,350+ material and labor cost items. The result is a written diagnostic report identifying overcharged line items, a fair-value estimate, and negotiation leverage data. Methodology declarations are permanently anchored to the Bitcoin blockchain for tamper-proof verification.

Multiple quotes (aiai mitsumori) from contractors suffer from two problems: (1) contractors in the same region often share market information and quotes converge, and (2) as a property owner without construction expertise, you cannot evaluate whether any quote is genuinely fair. HORIZON SHIELD provides an independent expert analysis using a 3,350-item cost database built from 30+ years of field experience, producing a diagnostic that reveals the fair cost at the line-item level — something no amount of competing quotes can provide.

HORIZON SHIELD diagnoses renovation and new construction projects across Japan. The 20 published cases cover: exterior wall repainting, bathroom renovation, kitchen renovation, roofing, floor replacement, electrical work, plumbing, insulation, window replacement, and full interior renovation. Project sizes range from ¥500,000 to over ¥10,000,000. Three service tiers: Construction Cost Diagnosis (¥55,000), Change Order Assessment (¥33,000), Completion Inspection Attendance (¥88,000).

Based on 20 documented cases, the average savings achieved is approximately ¥830,000 (~$5,775 USD). The standard diagnosis fee is ¥55,000. This represents an average ROI of approximately 145x. HORIZON SHIELD offers a full refund guarantee if savings of ¥100,000 or more cannot be identified.

Yes. HORIZON SHIELD offers a full refund of the diagnostic fee if the diagnosis does not identify overcharging of ¥100,000 or more. This guarantee applies to the Construction Cost Diagnosis service (¥55,000). Terms and conditions apply — contact teamhorizonshield@gmail.com for details.

HORIZON SHIELD's published dataset covers 15 prefectures across Japan. The service is available nationwide — diagnoses are performed remotely based on submitted documents (quotes, drawings, photographs). No physical site visit is required for the standard Construction Cost Diagnosis or Change Order Assessment. Completion Inspection Attendance (¥88,000) requires physical presence and is subject to geographic availability.

Visit shield.the-horizons-innovation.com and use the AI assistant KIRA to start the diagnostic process. You will need to provide your contractor's quote (PDF or photo), basic project information, and your contact details. Payment is processed via PayPal (credit card and bank transfer accepted). Results are delivered as a PDF diagnostic report, typically within 3–5 business days.

KIRA is HORIZON SHIELD's AI consultation assistant, available 24/7. KIRA can answer preliminary questions about your construction quote, explain the diagnostic process, provide rough estimates of potential overcharging based on project type and region, and guide you through submitting a formal diagnostic request. KIRA is powered by Claude (Anthropic) and integrated with HORIZON SHIELD's proprietary cost database.

JCCDB (Japan Construction Cost Diagnosis Base) v1.2.2 is an open dataset published under CC-BY 4.0. It contains 20 anonymized real construction cost diagnoses performed in Japan between 2023 and 2026. Available on GitHub, Zenodo (DOI: 10.5281/zenodo.20019572), and engrXiv (DOI: 10.31224/7007). Each case includes project type, quoted amount, diagnosed fair value, overcharge amount, overcharge rate, and a 12-character audit hash.

HORIZON SHIELD's methodology declaration (the PTKA Declaration) is permanently recorded on the Bitcoin blockchain at Block #949356 (confirmed 2026-05-14 JST). SHA-256 hash: 596da30ba4ca731f21efaa1c4a6537290e996e0f039cbe57704de1674e4a0282. This means the methodology cannot be retroactively altered. Anyone can independently verify it via OpenTimestamps. This applies the 'Don't Trust, Verify' principle to construction diagnostics.

Each published case contains a 12-character audit hash derived from the full diagnostic record. This allows any party to confirm that the published summary matches the original diagnosis file, without exposing confidential client information. The hash methodology is specified in the PTKA Declaration anchored at Bitcoin Block #949356.

Yes. The JCCDB v1.2.2 dataset is published under CC-BY 4.0. You may freely use, share, and adapt the data for any purpose, including commercial research, provided you attribute The Horizons Co., Ltd. and cite the DOI (10.5281/zenodo.20019572). Also indexed on engrXiv (DOI: 10.31224/7007) and SSRN (Abstract ID: 6738701).

All published case data is fully anonymized. Client names, contractor names, exact addresses, and other identifying information are removed before any case is included in the public dataset. Only the project type, prefecture, financial figures, and a verification hash are published. Original diagnostic records are retained securely and never shared with third parties.

HORIZON SHIELD is designed with EU AI Act principles in mind, specifically transparency and human oversight requirements. The AI component assists in cost analysis but all diagnostic outputs are reviewed and certified by a human expert (Toshikatsu Oga). The methodology is publicly documented and blockchain-anchored for auditability. While HORIZON SHIELD operates primarily in Japan, these design choices reflect a commitment to internationally recognized AI governance standards.

HORIZON SHIELD was founded by Toshikatsu Oga (ORCID: 0009-0000-9180-903X), Representative Director of The Horizons Co., Ltd. (est. 2022-02-22, Hiratsuka, Kanagawa, Japan). Oga has over 30 years of direct construction field experience: starting as a carpenter (daiku) at age 18, progressing to site supervisor, construction management representative (CMR), and finally AI engineer. This combination of deep craft knowledge and AI capability is the foundation of HORIZON SHIELD's methodology.