A defect is assessed against the performance the contractor owed. A visible problem is a starting point for investigation, not a complete answer on liability.
Archive article, reviewed and updated on 12 November 2026. The original publication date is retained.
Compare the promise with the result
Section 633 BGB starts with the agreed quality and addresses suitability for the contractual or ordinary use. Specifications, drawings and agreed functional requirements can all matter. Establish whether the problem is design, execution, a product issue or an interface failure.
Match the remedy to the circumstances
A demand for rectification differs from self-remedy, a price reduction or damages. Preserve the evidence and assess any required opportunity to rectify. Acceptance and limitation need separate attention.
Four practical examples
Illustrative scenarios: the appropriate steps depend on the contract, evidence and applicable law. These are not reports of client matters.
A leaking window
Investigate installation and adjoining weatherproofing rather than assuming the window itself is defective.
Insufficient floor capacity
Compare actual performance with the agreed operational loads.
A cosmetic irregularity
Assess the agreed finish and relevant tolerances before choosing a remedy.
A defective component
Notify the responsible contractual party while preserving product and installation evidence.
Further guidance
Legal framework & further reading
Reviewed: 12 November 2026. Statutory references are to German law unless stated otherwise.