Radon in Prague
Radon is a natural gas from the ground that you can neither see nor smell. In Prague there is mostly little or a medium amount of it, but more in places. Where, and when it makes sense to measure.
What radon is
Radon is a radioactive gas formed by the decay of uranium in rocks and soil. It has no colour or smell. It gets into buildings from the ground through gaps in the floor and foundations and builds up mainly in the cellar and on the ground floor. According to the World Health Organization it is the second most common cause of lung cancer after smoking, so it is worth knowing about when choosing a home.
How Prague is doing
The Czech Geological Survey maps the ground radon index in three levels: low, medium and high. Of Prague’s addresses, 35 % stand on ground with a low index, 63 % with a medium one and 1,9 % with a high one.
The highest share of addresses with a high index is in Řeporyje (36 % of addresses), Stodůlky (17 %) and Braník (15 %). The most addresses with a low index are in Benice (100 %), Březiněves (100 %) and Dolní Chabry (100 %).
We show the ground radon index for every address, neighbourhood and district. The map describes the surroundings at a scale of 1 : 50,000, so only a measurement can determine the radon index of a specific plot.
Flat or house
- A flat on a higher floor: little radon from the ground reaches you. The ground index is more of a rough guide.
- A ground-floor or basement flat: this is where radon matters most. With a high index, ask whether the building has ever been measured.
- A family house: in older houses without radon insulation, measuring makes sense mainly with a medium or high index. New buildings must have the plot’s radon index measured before construction, and the protection is designed to match.
How to measure radon
The radon concentration in a building changes with the weather and the season, so it is measured over the long term, ideally for several months during the heating season, with a small detector placed in a living room. The result is compared with the reference level of 300 Bq/m³ (annual average). The National Radiation Protection Institute offers measurements and advice on protection.
When there is a lot of radon
What helps most is regular ventilation, sealing the entry points from the ground (floors, pipe penetrations, the cellar) and, in houses, sub-floor ventilation. A specialist firm designs the specific measures based on the measurement.
Frequently asked questions
Where is radon highest in Prague?
According to the Czech Geological Survey’s radon index map, the most addresses with a high ground radon index are in Řeporyje (36 %), Stodůlky (17 %) and Braník (15 %). Across Prague it is 1,9 % of addresses.
Is radon a problem in a flat on a higher floor?
Radon gets into a building mainly from the ground, so it stays in the basement and on the ground floor. In flats on the upper floors of an apartment block its concentration tends to be low. Be careful mainly with a family house and a ground-floor flat.
What is the radon limit in a home?
The reference level in Czechia is 300 Bq/m³ as an annual average in living rooms. Only long-term measurement shows whether a building exceeds it.