Radon in Swiss homes: reference level, risk zones and what buyers must do

Radon (Rn-222) is a naturally occurring radioactive noble gas produced by uranium decay in soils and rock. It is colourless and odourless — impossible to detect by eye or nose. It seeps from the ground through cracks and joints into basements and ground floors, where it can accumulate. The problem: radon decay products lodge in the lungs and can damage cells there. In Switzerland, roughly 200–250 people die each year from lung cancer partly caused by radon.

Why radon matters when buying or renting

Unlike noise or tax rates, radon is invisible and site-specific: the risk depends primarily on the geology beneath a building and how it was constructed — not on the floor or the floor plan. A brand-new house in a high-risk zone can have higher radon than an old building in a low-risk area if sealing was neglected during construction. Anyone buying or renting long-term should know what radon ground lies under their building.

The Swiss reference level and what it means

The Radiation Protection Ordinance (StSV, SR 814.501) has set a reference level of 300 Bq/m³ for indoor air in existing buildings since 1 January 2018 (Art. 155). This is not a prohibition — it is not a binding limit in a criminal sense, but a reference point for action: if the measured concentration exceeds it, the FOEN recommends remediation.

Where is the risk highest?

Radon occurs wherever uranium is present in the ground — but concentrations vary enormously by geology, soil porosity and building type. In Switzerland the FOEN radon map reveals clear geographic patterns:

• Jura arc (high) — canton Jura (JU), Neuchâtel (NE), parts of Aargau (AG), Basel-Landschaft (BL) and Solothurn (SO): limestone with fissures allows radon to stream into buildings quickly.
• Parts of Graubünden (high to very high) — crystalline basement rock (granite, gneiss) with naturally higher uranium content.
• Pre-alpine regions and Mittelland pockets (medium) — varies by local geology; unevenly distributed.
• River valleys, lake shores, Geneva (low) — thick gravel and sand layers filter and dilute; GE, parts of ZH and VD are among the lower-risk regions.

On every municipality page on Homematch you can see the risk class of your target municipality and the average radon concentration — directly from FOEN data. This gives you an initial picture before you visit a property.

The only reliable method: measure

No risk map and no municipal figure tells you how much radon is in a specific building. For that, you need a measurement. In Switzerland this is done with passive dosimeters (track-etch detectors):

1. Order dosimeters — from the accredited laboratory Suissetest (Neuchâtel) or through the responsible cantonal office. Cost: CHF 30–80 per dosimeter incl. analysis.
2. Placement — in the lowest habitable space (basement, ground floor), in living or sleeping rooms, not in bathrooms or kitchens with active ventilation.
3. Duration — at least 3 months, ideally during the heating season (October–March) when windows are closed and concentrations are highest.
4. Results — the lab returns the mean in Bq/m³. Below 300: no action needed. Above 300: request remediation advice from FOEN or the cantonal authority.

What to do if radon is elevated

If the reading exceeds 300 Bq/m³, there are proven remediation approaches. FOEN recommends trying the cheapest measures first — they often suffice:

• Sealing — fill cracks and joints in the basement slab and walls. Inexpensive; often achieves 30–50% reduction.
• Underfloor ventilation — mechanically ventilate crawl spaces and service shafts to prevent radon from rising into living floors.
• Sub-slab depressurisation — a pipe below the slab that draws radon away before it enters and vents it outside. The most effective and common method; cost CHF 2,000–5,000; reduction up to 90% achievable.
• Mechanical ventilation with heat recovery (MVHR) — standard in new builds; dilutes radon through controlled air exchange.

FOEN offers free remediation advice and can refer you to specialists. Most remediations have low running costs (sub-slab depressurisation: under CHF 100/year in electricity).

For buyers: radon in the purchase contract

In Switzerland there is no legal obligation for sellers to disclose radon readings (unlike parts of the US or UK). However, purchase law (CO Art. 197 ff.) protects buyers against concealed material defects: if the seller knows of significant radon contamination and conceals it, this may constitute fraudulent misrepresentation. To be safe, have the purchase contract explicitly state that no known radon contamination above the reference level exists — or make the purchase conditional on the outcome of a measurement.

For renters: your rights with radon

As a tenant you can demand that the rental property be safe for health (CO Art. 256 — fit state). If radon above 300 Bq/m³ is proven, this may constitute a defect in the rental property. Depending on severity, you are entitled to give notice of defects, to a rent reduction or — if the landlord persistently fails to remediate — in extreme cases to extraordinary termination. Contact the cantonal conciliation authority or the Swiss Tenants' Association.

Radon in new builds: regulations from the drawing board

For new construction, a stricter standard applies: the StSV requires new buildings to be built so that radon stays below 100 Bq/m³ (planning value). In risk zones, radon protection measures are mandatory during construction: an airtight slab, connections for a future sub-slab system (even if not installed immediately). If you buy a new build in a high-risk zone, you should expect these measures to have been taken — ask for the relevant documentation.