Yes, if you failed to warn that the design or instructions were unsuitable although professional care would have revealed this. The defence “we followed the design” is not enough: the Commercial Code exempts a contractor only where it warned the employer, who then insisted in writing on using the items or instructions. Work must be suspended as necessary until the employer decides. A provable warning and the employer’s written insistence are therefore crucial; the site diary is the natural place to record them.
“We merely followed the design” is the contractor’s most common defence in a defects dispute, and it is insufficient on its own in court. The Commercial Code (Act No. 513/1991 Zb.) protects a contractor that spoke up, not one that built in silence.
Contractors are professionals and must speak up
The contractor must warn the employer without undue delay of unsuitable items received from it and instructions it gave, including design documentation, if professional care would have revealed their unsuitability. If unsuitable items or instructions prevent proper performance, work must be suspended to the necessary extent until the items are replaced, the instructions changed or the employer confirms in writing that it insists on them. The completion period is extended by the suspension, and the contractor is entitled to reimbursement of the related costs (§ 551(1) of the Commercial Code).
When you are not liable for defects
A contractor that has fulfilled the obligation under paragraph 1 is not liable for inability to complete the works or for defects in completed works caused by unsuitable items or instructions where the employer insisted in writing on their use in performing the works.
— § 551(2) of the Commercial Code (unofficial translation)
Exemption requires two conditions: you gave a warning, and the employer nevertheless insisted on use in writing. A contractor that gave no warning is liable for defects caused by unsuitable items or instructions (§ 551(3)). A contractor also avoids liability if even professional care could not have revealed the unsuitability, for example a hidden error in structural calculations that a construction company could not detect (§ 561).
What makes a warning stand up as evidence?
The law does not prescribe the warning’s form, but the contractor bears the burden of proof, and the employer’s insistence must expressly be in writing. Oral discussions at a site meeting are therefore insufficient in a dispute. A tried and tested approach is to enter the warning in the site diary and also send it by letter or email with confirmation of delivery, identify precisely what is unsuitable and the likely consequences, and ask the employer to decide. If the employer insists on the original solution, request a written statement; do not restart the affected work until it is provided. Email is usable evidence if you can prove sending and who acted on behalf of the sender; with contentious employers, a letter with proof of delivery or a signature in the diary is more reliable.
Our disputes experience is clear: what matters is what was recorded and delivered, not what the parties remember.
Remember the employer’s defect notification deadlines
If the employer nevertheless raises defects, it must meet the applicable deadlines: notification without undue delay after discovering them or when they should have been discovered, and within two years, or five years for buildings, of handover (§ 562). We explain defect remedies and warranties in construction contracts in our answer on defects and warranties under a construction contract.
How we can help
We structure your construction contract to give warnings, work suspension and variations clear procedures and records. In an existing dispute, we assess whether the warning and the employer’s insistence stand up as evidence and handle the defective works dispute. We maintain construction companies’ documentation and procedures through ongoing legal services for construction companies.
If you are currently facing an unsuitable instruction from the employer, contact us before carrying it out: a warning cannot be written retrospectively.
This answer provides general information on the law as at 5 September 2026. It does not constitute legal services or replace an assessment of an individual case. The details of your situation may differ. Book a consultation to discuss them.
