Radon in New Buildings: Legal Duties, Liability and Sanctions Under Czech Law

9.4.2026 | ARROWS law firm

Radon in new buildings poses a hidden legal and financial risk that may only become apparent years later. Although the Atomic Act sets strict preventive rules, designers and developers often operate in a grey area of liability. In this article, you will learn what the statutory obligations are, what sanctions may apply, and how to address a situation where a building fails to meet the limits.

The photograph shows a specialist consulting on radon-related legal risks.

Article contents

Radon as a hidden threat in new builds
Legislative framework: What the Atomic Act specifically requires
Liability of the site manager and construction supervision
The role of the developer and the investor in radon prevention
Sanctions and legal consequences of breaches of obligations
How to minimise risks during construction

Quick summary

The Atomic Act sets strict rules: Anyone designing a new building with residential or occupancy space must ensure that the radon index of the plot is determined. The previous leniency for buildings on low-risk plots has been abolished, and protection must always be addressed preventively.
Responsibility lies with both the designer and the contractor: The designer is responsible for the correctness and completeness of the proposed anti-radon measures. This responsibility, together with the contractor’s responsibility for execution, may be asserted for five years from the handover of the building.
You need a specialist: Given the technical complexity and legal risks, it is advisable to entrust the coordination of radon prevention to professionals. ARROWS, a Prague-based law firm, routinely handles this agenda and helps clients avoid fines and legal disputes.

Radon as a hidden threat in new builds

Radon is not only a health risk. From a legal and economic perspective, it represents an invisible threat for developers, designers and site managers, which may manifest itself months or years after the building approval process is completed. Unlike visible construction defects, radon will not be detected during a standard inspection, it is not visible on the surface, and it cannot be easily remedied without additional construction works.

The obligation to measure radon and apply anti-radon measures is enshrined in the Atomic Act (Act No. 263/2016 Coll.). The Act defines the radon index of a plot as a risk indicator; however, reality is more complex. Data from the Czech Republic show that radon can accumulate in houses even when the plot’s radon index is classified as low, if the building is not sufficiently insulated.

Legislative framework: What the Atomic Act specifically requires

Act No. 263/2016 Coll., the Atomic Act, as amended, clearly defines the obligations of all participants in the construction process for buildings with residential or occupancy space. It is a comprehensive regulation affecting designers, site managers, construction supervisors, owners and developers.

The key obligation is unambiguous: anyone proposing the siting of a new building or an extension with residential or occupancy rooms is required to ensure that the radon index of the plot is determined and to submit the results to the building authority. The State Office for Nuclear Safety (SÚJB) has long been dealing with situations where this obligation is breached, circumvented or misinterpreted. In practice, it therefore pays to set up contractual and project processes so that they stand up to an inspection and any potential dispute, which typically falls within the scope of development and construction law.

The plot’s radon index and its practical implications

The plot’s radon index is not merely a theoretical number. It is a parameter that determines what measures against radon ingress must be designed in the project and later implemented. The Act and the related radiation protection decree distinguish between three categories: low, medium and high radon index.

Previously, it was believed that no special measures were necessary on plots with a low radon index. However, current Czech legislation and technical standards require preventive protection of the building against radon ingress from the subsoil virtually always. Even on plots with a low index, elevated radon concentrations may occur in new houses if the house is too airtight and lacks basic insulation against ground moisture and gases.

Reference levels: 300 Bq/m³

Legislation defines a key threshold, the so-called reference level. Under Section 96 of the Atomic Act and Decree No. 422/2016 Coll., the reference level for the volumetric activity of radon in indoor air is set at 300 Bq/m³. This value applies to both new and existing buildings.

In practical terms: if your new build shows values above 300 Bq/m³ after completion, it does not meet the radiation protection requirements. If, at this stage, the impacts on the further progress of construction or use are also being addressed, it may be useful to know when an environmental factor can lead as far as restricting operations; see when air pollution may be a reason to stop construction or operations. For the designer, site manager and developer, this means that the obligation to properly design or implement the protection was likely not met.

Designer’s liability for the design of anti-radon measures

The designer is responsible for the design of the structure under the new Building Act No. 283/2021 Coll. This responsibility continues even if the designer delegates part of the work to a specialist. The legislation provides that the designer is responsible for the correctness, integrity and completeness of the design documentation. For interventions in structures and documentation in apartment buildings, similar responsibility in practice also extends to layout changes and interventions in common areas, which is discussed in more detail in the article change of an apartment layout in an apartment building: intervention in common areas, structural integrity and liability.

In practice, this means that if the designer proposes insufficient anti-radon measures in the technical report or drawings and it later turns out that radon in the completed building exceeds the limit, the designer bears liability for this defect. The client commissioning the construction has the right to claim damages or a discount on the price of the work from the designer.

Mandatory standards and norms

The designer must proceed in accordance with legal regulations and technical standards. In the area of anti-radon prevention, the key standard is ČSN 73 0601 – Protection of buildings against radon from the subsoil. This standard describes in detail how radon protection is to be designed depending on the radon index of the plot and the type of structure.

Although technical standards are generally recommendatory, in the case of protecting health and the safety of a building, compliance with them is considered fulfilment of a statutory obligation. If the designer proposes a solution contrary to this standard and the building subsequently fails to meet the limits, the designer’s position in any court dispute will be very weak.

Specific obligations of the designer within the project

The designer must define in the design documentation:

The radon index of the building based on measurement of the plot’s index.
The type of anti-radon measure (waterproofing, subsoil ventilation, ventilation layers).
Technical details such as the routing of the insulation or airtight penetrations of utility networks.
Calculations for sizing the insulation in accordance with ČSN 73 0601.

If the designer omits any of these points or prepares them poorly, the defect often becomes apparent only during measurements in the completed building.

Designer’s liability and time limits

The designer bears liability for defects in their design. Under the Czech Civil Code, defects in a building (including design defects that manifested in the building) may be claimed for up to five years from acceptance of the building.

Risks and sanctions	How ARROWS can help (office@arws.cz)
Exceeding the reference level of radon in the completed building: After completion, the client commissioning the construction finds that the measured radon concentration exceeds 300 Bq/m³, which requires remediation.	Project analysis and identification of liability: ARROWS attorneys in Prague will arrange an assessment of whether the designer made an error in the design and will prepare the legal arguments.
Financial costs of additional measures: Additional remediation (e.g., installation of forced ventilation) is significantly more expensive than preventive measures.	Recovery of compensation: We represent investors in recovering remediation costs from the responsible parties (designer, contractor).
Disciplinary proceedings before ČKAIT: The designer may be subject to disciplinary proceedings by the Czech Chamber of Authorised Engineers and Technicians (ČKAIT) for professional misconduct.	Legal support: We prepare documentation for complaints or defence proceedings within professional chambers.

Liability of the site manager and construction supervision

The site manager and construction supervision play a key role during implementation. The site manager is responsible for compliance with the design documentation, including correct installation of insulation. Construction supervision has a duty to monitor the quality of the works.

In practice, errors occur particularly in the execution of insulation and utility penetrations, which compromise the gas-tightness of the building envelope.

Obligations under the Building Act

Under the new Building Act, the site manager is obliged to ensure proper organisation of the construction site and management of the construction in accordance with the execution documentation. In the radon context, this means:

Supervising the integrity of the anti-radon insulation.
Ensuring gas-tight execution of installation penetrations (water, sewerage, electrical).
Preventing the formation of cracks in contact structures.

Construction supervision is obliged to monitor the method and procedure of construction, in particular the safety of installations and operation. If the supervisor overlooks damaged insulation, they may bear co-liability for defects in the building under Section 2630 of the Czech Civil Code.

Contact our experts

Mgr. Karel Huneš

associate

hunes@arws.cz

JUDr. Tereza Snopková, Ph.D.

associate

snopkova@arws.cz

The role of the developer and the builder in anti-radon prevention

The developer or builder is obliged to ensure that the radon index of the plot is determined and to submit the results to the building authority (Section 98 of the Atomic Act). They cannot avoid liability merely by referring to the designer if they did not provide the designer with correct documentation.

Developer’s obligations at individual stages

Preparation: Arrange measurement of the plot’s radon index by a company holding a permit from SÚJB (the State Office for Nuclear Safety).
Design: Contractually oblige the designer to propose measures in accordance with ČSN 73 0601.
Implementation: Monitor (directly or through technical supervision) the execution of insulation works.
Occupancy approval/Completion: Arrange radon measurement in the completed building if required by law.

Contractual allocation of liability

ARROWS, a Prague-based law firm, strongly recommends that contracts with suppliers include clear radon clauses. The contract for work should specify that the work will be free of defects and that the radon concentration will not exceed the reference level of 300 Bq/m³. Without these provisions, recovery of remediation costs may be complicated.

Radon measurement: obligations and practical aspects

The law distinguishes between two types of measurements, which must not be confused.

Measurement of the plot’s radon index

This is carried out before construction begins, directly on the plot. It must be performed by a holder of an SÚJB permit. The result is classification of the plot into a category (low, medium, high index), which serves as an input for the designer.

Measurement of radon activity concentration in the completed building

This measurement verifies whether the measures were effective. Under the Atomic Act, it is mandatory to ensure this measurement when putting a new building with residential or occupancy space into use, unless the building is located on a plot with a low radon index.

If measurement in the completed building shows values above 300 Bq/m³, the building does not fully comply with the legislative requirements for prevention. In such a case, it is necessary to identify the cause, which is most often a design defect or a defect in execution.

Sanctions and legal consequences of breach of obligations

The State Office for Nuclear Safety (SÚJB) or building authorities may impose fines. For failing to ensure the determination of the radon index of the plot, both individuals and legal entities face a fine of up to CZK 500,000 (for certain specific obligations relating to public buildings, the upper limit may be higher).

Further sanctions may be imposed under the Building Act for carrying out construction in breach of the approved documentation.

Liability for damage and defects

However, the greatest financial risk for a developer and contractor is not administrative fines, but claims arising from construction defects. The buyer or client may request:

Remedy of the defect: At the expense of the contractor or designer.
A price reduction: If the defect cannot be remedied or if the parties agree to this.
Compensation for damage: For example, the costs of expert opinions or increased energy costs due to forced ventilation.

The limitation period for asserting hidden defects in real estate is five years from the acquisition of title (or, as applicable, handover of the building). Radon, which cannot be seen or smelled, is a typical example of a hidden defect.

Risks and sanctions	How ARROWS can help (office@arws.cz)
Fine imposed by an authority: Sanctions for missing measurements or documentation.	Administrative proceedings: We represent clients in proceedings before authorities, file appeals, and minimise the impact.
Damages dispute: The client or buyer sues the developer due to defects (high radon levels).	Court representation: We handle disputes over defects in works, secure the evidentiary position, and negotiate settlements.
Decrease in property value: A property with high radon levels is harder to sell.	Legal structuring of the discount: We help set fair terms for the settlement between the seller and the buyer.

How to minimise risks during construction

Contracts: Ensure that contracts with the designer and contractor clearly address liability for anti-radon measures.
Qualifications: Work with designers who are familiar with the ČSN 73 0601 standard.
Supervision: Ensure that the investor’s technical supervisor checks that insulation layers are intact before they are covered (floor concreting).
Measurements: Do not cut costs on radon measurements. Carry them out thoroughly both before construction and after completion.

Legal aspects when purchasing or renting a building with radon

If you buy a property and subsequently discover high radon concentrations that the seller did not inform you about, this constitutes a hidden defect. Under the Czech Civil Code, you have the right to notify the defect within 5 years of acquiring ownership.

If the property has a defect that prevents its proper use or reduces its value, you are entitled to an appropriate reduction in the purchase price or to remedy of the defect. In extreme cases, termination of the contract may be considered.

Procedure for buyers

Measure radon: Ideally by longer-term measurement (at least one week during the heating season).
Make a claim: Notify the seller of the defect without undue delay after discovering it.
Resolve: Request a discount corresponding to the remediation costs or the implementation of corrective measures.

Conclusion

Radon in new builds is a topic that combines building physics with hard law. The Atomic Act and the new Building Act set clear rules, and ignoring them can be costly.

Key takeaways:

Every new build with residential premises is subject to the obligation to determine the radon index of the plot.
Both the designer and the contractor are responsible for ensuring that the building does not exceed the reference level of 300 Bq/m³.
Buyers have strong rights under liability for hidden defects for a period of 5 years.
Prevention (quality contracts and supervision) is always cheaper than subsequent court disputes and remediation.

Specialists from ARROWS, a Prague-based law firm, handle these matters and can effectively set up processes, prepare contracts, and protect your rights. Simply email us at office@arws.cz.

FAQ – Most common legal questions about radon in new builds

1. Do I need to have the radon index of the plot measured for every new build?
Yes, if it is a building with residential or occupied premises. This obligation follows directly from Section 98 of the Atomic Act. The measurement results are a mandatory annex for the building permitting procedure.

2. What happens if I measure radon in a completed new build and it exceeds 300 Bq/m³?
This is an exceedance of the reference level. It means the building does not meet the parameters it should. The owner should seek to reduce this level. If the exceedance occurred due to an error in the design or execution, the costs should be borne by the party at fault (designer/contractor).

3. Is radon a hidden defect when buying a house?
Yes, it is generally considered a hidden defect because it cannot be detected by a standard inspection. The buyer has the right to assert defect claims within 5 years of taking over the property.

4. Can I disclaim liability for radon in a contract with a designer?
You cannot fully disclaim liability for a breach of law or gross negligence. However, it is possible to limit damages if the law does not prohibit this for the given type of contractual relationship (beware of consumer contracts). We always recommend consulting a lawyer.

Notice: The information contained in this article is of a general informational nature only and is intended for basic guidance based on the legal position as of 2026. Although we take the utmost care to ensure accuracy, legal regulations and their interpretation evolve over time. We are ARROWS, a Prague-based law firm, an entity registered with the Czech Bar Association (our supervisory authority), and for maximum client security we are insured for professional liability with a limit of CZK 400,000,000. To verify the current wording of regulations and their application to your specific situation, it is necessary to contact ARROWS directly (office@arws.cz). We accept no liability for any damage arising from the independent use of the information in this article without prior individual legal consultation.

Read also: