What is the duty to warn?

The duty to warn (Dutch: waarschuwingsplicht) is a contractor’s legal obligation to warn the client about errors and risks that they see, or reasonably should have seen, in what the client supplies or prescribes. In the Netherlands it is set out in Article 7:754 of the Dutch Civil Code and applies both when the contract is concluded and during execution.

What must the contractor warn about?

Errors in the brief, such as a design that cannot work.
Errors in the client’s drawings, calculations, specification or execution instructions, or those of the client’s advisers.
Defects or unsuitability of materials and tools supplied or prescribed by the client.
Defects in the ground or existing structures on which the work is built.

What changed with the Wkb?

Under the Dutch Quality Assurance for Building Act (Wkb), a second paragraph was added to Article 7:754 from 1 January 2024. The warning must now be in writing (for example a letter, email or text message), clear and understandable, and must state the possible consequences for the work. Contracts may not deviate from this to the detriment of a private (consumer) client. Projects under the Dutch UAV 2012 conditions contain a similar duty in paragraph 6.

Requirements for a written warning under the Wkb

Warning is in writing: For example a letter, email or text message.
Warning is clear and understandable:
Warning states the possible consequences: The possible consequences for the work must be stated.

Requirements for a contractor's warning under Article 7:754 paragraph 2 of the Dutch Civil Code, added under the Dutch Quality Assurance for Building Act (Wkb) from 1 January 2024. Contracts may not deviate from this to the detriment of a private (consumer) client. Applies in the Netherlands; in other countries the rules differ, so check local law and your contract conditions.

Consequences

If the contractor fails to warn when they should have, they can be liable for the damage, even if they carried out exactly what was prescribed. If they do warn and the client still opts for their own solution, the risk largely shifts to the client.

Tips

For contractors and tradespeople working for others:
1. Warn as early as possible and always in writing.
2. Describe specifically what the problem is, what could go wrong and which alternative you recommend.
3. Ask the client to respond in writing and keep everything in the project file.

For clients:
1. Take a warning seriously and get independent advice if needed.
2. Record your decision; if you go against advice, you usually carry the risk yourself.

In other countries similar principles exist, but the rules differ; check local law and your contract conditions.

Related terms

Contractor
Subcontractor
The UAV
Construction defect
Hidden defects

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