Radon gas in the Madrid mountains: myths and realities of a silent risk

The Madrid mountains are a zone II area, the one with the highest exposure to radon gas. But actual measurements vary so much that concern can be disproportionate.

The decision to move to Valdemorillo or its surroundings brings with it a geological debate: the granite terrain favours the release of radon, a naturally occurring radioactive gas. However, the concentration inside a home depends on very specific factors: the type of foundation, the presence of a basement, ventilation, materials and even how the rooms are used. Two adjacent houses can give radically different readings.

Is it really dangerous? The smoking nuance
Radon is the second leading cause of lung cancer after smoking, but the interaction between the two is key. A study by Spain's Ministry of Health cited in the discussion points out that most cases attributable to radon occur in smokers and former smokers. In non-smokers, the risk is much lower, except in extreme exposures such as those of miners. This puts the alarm into perspective: properly ventilating the lower floors and, above all, not smoking, are more effective measures than obsessing over the gas.

Solutions: from DIY to 6,000 euros
For anyone building a chalet with a basement, radon accumulates in the lower part and can seep into the home if no measures are taken. Options range from a professional system costing around 6,000 euros – with a depression well and a permanent extractor – to a homemade solution: a perforated plastic sump buried under the ground slab, connected to an extraction pipe with a pump. The cost of the second option is under 400 euros, and it can be installed yourself. That said, there are no guarantees of total effectiveness unless the ground is properly sealed.

Measure before you antiestéticar
The recurring recommendation is clear: measure. A home radon detector costs around 50 euros and provides enough guidance to know whether the concentration exceeds 100 becquerels per cubic metre (the WHO reference level). In one real case, the basement average was 74 bq/m³, with peaks of 150. On upper floors, levels are usually much lower. Spain's building regulations already require anti-radon barriers in risk areas, but they do not replace on-site verification.

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The dilemma remains open: radon is a real but very localised and manageable risk. For a smoker sleeping in a habitable basement, the threat is high. For a non-smoker living on a well-ventilated first floor, there is far less to worry about. As so often, the devil is in the details.