Twelve items to confirm: work scope, handover date, contract amount, change-order rules, defect liability, warranty, insurance, termination, dispute resolution, stamp duty, attached drawings, and consumption tax. Watch out for vague "to be discussed" clauses. Your architect can review the contract independently.

A construction contract is a document that settles a transaction of tens to hundreds of millions of yen on just a few pages. After you sign and seal, the terms generally cannot be changed, and most trouble that arises later is rooted in "insufficient checking at the contract stage." Put the other way, a few tens of minutes of careful reading before sealing prevents most of it. We organise what to check — and why — through 12 essential items and the typical disputes.

1. Why checking the contract matters

The contract matters this much because what finally settles "he said / she said" is the document, not a verbal promise. However carefully you are briefed in meetings, if it is not in the contract and attached documents it is treated as "outside the contract" and becomes grounds for extra cost or a spec change. Custom homes and residence-class builds especially, with their high spec freedom, tend to accumulate verbal agreements, and that gap turns straight into a money dispute. With 30–40 minutes of careful reading — even fixing just the four points of work scope, amount, handover date and warranty — you can prevent most later trouble. The more the other party rushes you to seal, the more it is worth pausing to read.

2. The 12 items you must check

  1. Work scope: state whether it is the main works only or includes ancillary works (exterior, demolition, ground improvement)
  2. Handover date: fix the period and handover date by calendar date; check the damages clause for delay
  3. Contract amount (tax incl.): the basis for the consumption-tax calculation, and whether an itemised breakdown is attached
  4. Payment schedule: 30% at contract / 30% at framing / 40% at completion is typical
  5. Rules for additions/changes: documentation, the estimate-approval process, and settlement at final payment
  6. Defect liability: structurally essential parts are 10 years by law; rainwater-ingress points are also 10 years
  7. Warranty periods: a list of part-by-part warranties — equipment (2 yrs), finishes (1–2 yrs)
  8. Damage insurance: fire and storm/flood during works are, in principle, insured at the builder's responsibility
  9. Termination clause: conditions, penalty, and settlement of work already done
  10. Dispute resolution: the court of jurisdiction, and whether ADR (Construction Dispute Committee) applies
  11. Stamp duty: borne by the owner per the amount — ¥60,000 for ¥100M
  12. Document list: check the list of design documents (design, structure, services) tied to the contract

Of these 12, trouble concentrates on three: (1) work scope, (2) handover date and (5) the addition/change rules. If the line of "what is included in the contract amount and what is separate" is vague, exterior works or ground improvement can become a later claim of millions of yen. The trick is to cross-check not just the contract body but the attached itemised breakdown and the design documents, confirming that amount, spec and scope all agree. Item (6) defect liability (structure and leaks are 10 years by law) and (7) part-by-part warranty are easily confused, so grasp "what the law protects" and "the company's own warranty" separately.

3. The "vague clauses" to watch especially

The most dangerous thing in a contract is plausible-looking vague wording. Phrases like "by separate consultation," "actual-cost settlement on spec change" and "per standard spec" leave the amount unfixed at that point and become a "blank" the builder can later fill with an extra charge at their discretion. If it says "ground improvement to be consulted separately after survey," you are signing while leaving room for tens to hundreds of thousands of yen to be added depending on the survey. The fix is simple: when you find a vague clause, do not leave it as "to be consulted" — make it concrete in an attached sheet with a cap amount, conditions and assumed cases. Reading the clauses one by one with your designer, confirming the design documents and contract agree on the fixed spec, is the sure approach.

4. Common disputes

What these share is that each is caused by "it wasn't written in the contract / it was vague" — not by a problem of construction quality itself. So even with a fine builder, the same trouble can occur if the contract's precision is low. Delay damages in particular: without explicit wording, the principle is "no claim even if late." It is safest to fix the handover date by calendar date and write in the damages per day of delay. Spec-grade gaps are prevented by putting maker name, product number and grade into the documents.

5. Risk-avoidance before contract

  1. Take a reading period of a week or more (do not rush to seal)
  2. Third-party review by the design office (usually included in the design-supervision contract)
  3. Document every addition/change — state this rule in the contract
  4. Unify the consumption-tax notation (tax-incl. / tax-excl.)
  5. Do not leave unclear points as "to be consulted" — fix them by addendum or attached sheet

The most effective is no. 2, the third-party review. Having a disinterested designer check the contract the builder prepared fills the holes in scope, warranty and payment terms that an owner tends to miss. If you have a design-supervision contract, this check is usually part of that work. The practical order: first secure a week of reading, list your questions and hand them to the designer, fix them by attached sheet, then seal. Even when told "please seal quickly," this is the one place worth spending time.

A contract is not "something to bind the other side" but "something that protects both sides." For the builder too, a clear contract prevents disputes. Our design office supports the contract checkpoints, so please consult us before you seal.

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