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Radon: the building-code map and when measuring is worth it

Radon is a natural radioactive gas that rises from granitic ground and accumulates in ground floors and basements. Since 2019 the Spanish building code classifies municipalities by exposure potential and requires measures in new builds where the risk is higher. For an old building, the map tells you whether measuring is worth it.

The CTE zones

Basic document DB-HS6 (RD 732/2019) assigns each municipality a zone: unclassified (low potential), zone I (basic measures in new builds: protective barrier) and zone II (reinforced measures: barrier plus ventilated cavity or depressurisation). Galicia, western Castilla y León, Extremadura, parts of Madrid, Catalonia and the Cantabrian coast have many municipalities in zones I and II. The map is municipal: within one municipality there are parcels with and without radon.

What it implies

For buying an upper-floor flat: little. For a house, a ground floor or an inhabited basement in zone II: a three-month measurement (€30–60 for the detector) before signing or just after, and if it comes out high (the European reference is 300 Bq/m³), forced ventilation or sealing, which costs from hundreds to a few thousand euros. The Nuclear Safety Council publishes a radon-potential map with more detail than the CTE.

What the PropVer report does

It says which CTE zone the municipality is in and therefore what the code would require of a new building; it measures nothing. If the property is a ground floor or a detached house in zone I or II, the report marks it as attention and tells you to measure.

Check it yourself

Check your property in two minutes

Address, cadastral reference, coordinates or a click on the map. If it is in the service area, the report is free during the beta.

Check a property

More guidesWhat to check before buying property in Spain The cadastral reference: the key to a Spanish property Planning: what you can do with the parcel, and what can be done to it Flood zones: what the map knows and the viewing does not Contaminated soils: what the deed must say and the listing never does The history of the ground: eighty years of aerial photographs Noise: what the midday viewing does not tell you Masts and the grid: what is on record, and how far ITE, IEE and the energy certificate: the levy that is coming and the bill you will pay Water and discharges: whether the tap ran last summer

Updated 2026-10-23.