Natural hazards in Switzerland: check earthquakes, radon, avalanches and landslides for your address
In a mountainous country, natural hazards come with owning property. This page explains which hazards planners and insurers check, which values and zones apply – and how to look up what applies to a specific address instead of finding out after the purchase.
- 1 – 3bSeismic zones (SIA 261)structural design
- 0.6 – 1.6Ground accelerationm/s², zone 1 to 3b
- 300Radon reference levelBq/m³, living spaces
- red · blue · yellowHazard zonesmunicipal hazard maps
Why natural hazards matter when buying
Earthquakes, radon, avalanches and landslides are hard to change after a purchase, and you can't see them at a viewing. The suntag.ch report shows these four layers as federal overview maps. They are a first orientation and show where to ask questions; the binding documents are held by the municipality and the canton.
Earthquakes: the zones under SIA 261
Standard SIA 261 divides Switzerland into seismic zones from 1 to 3b, based on the maximum expected ground acceleration over a 475-year return period:
| Zone 1 (lowest) | 0.6 m/s² |
| Zones 2 and 3a | in between |
| Zone 3b (highest) | 1.6 m/s² |
The highest zones are mainly in Valais and the Basel region, where the standard requires stronger structural design. Older buildings were rarely designed for earthquakes, which matters most in zones 2 and 3. For an older building, ask about the design.
Radon: an invisible gas in buildings
Radon is a natural radioactive gas that can seep into buildings from the ground. A reference level of 300 Bq/m³ applies to rooms where people stay regularly. If it is exceeded, the Radiation Protection Ordinance provides for remedial measures. Only a measurement in the building gives the real value.
Reading the radon map
The radon map doesn't show measured values but the probability, in per cent, that a building exceeds the reference level of 300 Bq/m³:
| 1% or less | low risk |
| above 20% | roughly one building in five exceeds the reference level |
| high probability | a simple measurement over a few winter months is advisable |
A higher radon potential shows up in the Jura, Ticino and Graubünden, among other areas. A measurement is inexpensive and can be done in everyday life.
Avalanches and landslides
The overview maps from SilvaProtect-CH show where avalanches and debris flows (fast-moving mixtures of soil and water on open slopes) can occur. They matter most for mountain locations and are only a first indication. The binding documents are the hazard maps of the municipality or canton, which distinguish three zones at parcel level: red (building ban), blue (building with conditions) and yellow (awareness). So look at the slope above your point, not only at the point itself. Other hazards such as floods or rockfall are not covered by the report; the municipality's hazard map tells you about those.
What to check when buying
- Ask the municipality or canton for the hazard map of the parcel, especially in the mountains.
- Look at the slope above the plot: where could avalanches or landslides come from?
- For an older building in seismic zones 2 and 3, ask about the earthquake design.
- If the radon potential is elevated, plan a measurement over a few winter months.
- Check which hazards the report doesn't cover (for example floods, rockfall) and ask the municipality.
Look up the natural hazards for your own address
The suntag.ch report shows, for any address in Switzerland and Liechtenstein, the seismic zone under SIA 261, the radon potential and the avalanche and landslide hazard. It also covers sun exposure day by day across the whole year, road, rail and aircraft noise, car and public-transport access, fibre, 5G, mobile antennas, radio and TV transmitters, high-voltage installations, solar potential and zoning – a 31-page PDF report with 11 charts, 30 maps and 3 tables from CHF 15.
Frequently asked questions about natural hazards
Which seismic zone is my address in?
The seismic zone map under SIA 261 shows it (zones 1 to 3b). The suntag.ch report displays it for your address. The highest zones are mainly in Valais and the Basel region.
At what level is radon a problem?
A reference level of 300 Bq/m³ applies to rooms where people stay regularly. If it is exceeded, the Radiation Protection Ordinance provides for remedial measures. Only a measurement in the building gives the real value.
What does the percentage on the radon map mean?
It is the probability that a building exceeds the reference level of 300 Bq/m³. At 1% or less the risk is low; above 20%, roughly one building in five exceeds the level and a simple measurement over a few winter months is advisable.
Are the avalanche and landslide maps binding?
No, they are only a first indication. The binding documents are the hazard maps of the municipality or canton, with the zones red (building ban), blue (building with conditions) and yellow (awareness).
Which natural hazards does the report not cover?
The report covers earthquakes, radon, avalanches and landslides. Other hazards such as floods or rockfall are not included; the municipality's hazard map tells you about those, also via the national portal naturgefahren.ch.
See also: Property checklist for Switzerland →
See also: Sun exposure in Switzerland →
Sources and methodology: Seismic zones: standard SIA 261, data from the Federal Office for the Environment (FOEN), 475-year return period. Radon: Federal Office of Public Health (FOPH), reference level 300 Bq/m³ under the Radiation Protection Ordinance. Avalanches and landslides: SilvaProtect-CH, FOEN. The maps are national overview maps, not parcel-level hazard maps, and do not replace an official assessment or a measurement. More information: naturgefahren.ch, slf.ch, seismo.ethz.ch, ch-radon.ch, map.geo.admin.ch.