The importance of ventilation in combating radon
- Mikael Denut
- Feb 23
- 5 min read
Radon (Rn-222) is a significant health risk for Finnish households that cannot be detected with the senses. It is an invisible, odorless, and tasteless noble gas that is produced as a decay product of uranium (U-238) and radium (Ra-226) in the soil. Finland is one of the countries with the highest indoor radon concentrations in the world, due to, among other things, the uranium content of our granitic bedrock and permeable gravel areas, such as ridges. However, the radon concentration in the soil can be significantly influenced already during the construction phase by choosing the right base floor structures
Although radon originates from the soil, its accumulation in dangerous concentrations inside a building is often a direct result of structural characteristics and ventilation operation.
The physics behind radon: Negative pressure and the “chimney effect”
In Finland, the movement of radon into buildings is governed by a basic law of physics: air flows from higher pressure to lower. Finland’s climate and construction methods create two significant factors in this process:
Temperature differences and the chimney effect: In winter, warm indoor air rises and exfiltrates through the upper parts of the building. This creates negative pressure in the lower part of the building, especially at floor level.
Mechanical ventilation: Mechanical exhaust ventilation, popular in Finnish homes, is designed to keep the building slightly depressurized (under negative pressure) to prevent moisture from condensing in the structures. If the ventilation is unbalanced, the negative pressure becomes too high. Although previously (RakMK D2) buildings were often operated noticeably depressurized to avoid moisture damage, the current regulation (1009/2017) and guidelines emphasize balanced ventilation. The goal is to achieve only a very small pressure difference of approximately 0…–10 Pa across the building envelope. A controlled pressure difference is necessary to prevent the transfer of soil contaminants and radon into indoor air.
This negative pressure acts like a vacuum cleaner, drawing radon-rich soil pore air into the interior through small cracks, penetrations, and concrete shrinkage joints in the slab. Radon concentrations in soil pore air can be as high as 10,000–100,000 Bq/m³, so even a small leak can significantly increase indoor air concentrations.
The Role of Ventilation: Threat and Solution
Ventilation is a double-edged sword in the fight against radon. If adjusted incorrectly, it worsens the problem, but if implemented correctly, it is an effective part of the solution.
Negative pressure control
If the radon concentration in a home is high, the first thing to check is often the ventilation balance. Excessive negative pressure draws radon from the ground. By adjusting the supply and exhaust air to the correct ratio, the inflow of radon can be significantly reduced. However, it must be remembered that simply increasing ventilation is not always enough if radon is entering in large quantities; in this case, structural measures are needed.
Dilution effect
Effective and continuous ventilation dilutes the radon gas that has entered. In older buildings with gravity ventilation, radon concentrations often rise significantly during the winter months, when ventilation is reduced and the chimney effect is at its strongest.
Technical control methods
In Finland, new construction is governed by strict legislation (Radiation Act 859/2018). The design value for new buildings is 200 Bq/m³ and the reference value for existing homes is 300 Bq/m³. According to the decree of the Ministry of Social Affairs and Health (1044/2018), the reference value for radon concentration in homes and other living spaces is 300 Bq/m³. In the best indoor air quality classes (S1 and S2), the target is even below 100 Bq/m³.
1. Radon piping and suction: Since 2004, passive under-slab radon piping has been installed in the foundations of single-family homes. It collects radon gas from under the building before it enters and vents it to the roof. If concentrations still remain high, a radon fan (radon suction) is connected to the piping, making the system active and creating a lower pressure under the slab than indoors so radon-laden soil air is drawn into the pipe and discharged outdoors. The effectiveness of radon piping is based on collecting the gas before it enters the structures. If the passive system is not sufficient, the fan creates lower pressure in the soil than inside the building.
2. Sealing: Sealing the joints and penetrations in the slab with elastic compounds or bitumen membranes is essential. Without sealing, the ventilation system will draw radon in along the easiest route. Special attention must be paid to slab joints, concrete shrinkage joints, and pipe penetrations. Sealing ensures that make-up air is not drawn uncontrollably through the soil, which is a common problem, especially in buildings with strong negative pressure.
Health risks and the importance of measurement
Radon is the second leading cause of lung cancer in Finland after smoking. An estimated 300 Finns die each year from radon-induced lung cancer. The risk is many times higher in smokers, but radon is also the leading cause of lung cancer in non-smokers (approximately 40 cases per year). After fine particles, radon is the second most significant factor increasing the burden of indoor air disease in Finland. Exposure is completely asymptomatic, and the effects only become apparent after a delay of years. Reliable concentration determination requires at least two months of measurement during the heating season; the most representative period is typically between early November and late April. This is necessary because radon concentrations vary greatly depending on the season and weather conditions.
Since radon cannot be smelled or seen, the only way to be sure of the safety of your home is to measure it. The Radiation and Nuclear Safety Authority (STUK) recommends measuring during the heating season (1 September–31 May) for at least two months, preferably three months. Short “quick tests” do not give a reliable picture of the annual average, as weather conditions and ventilation use vary daily.
Ventilation plays a key role in radon management: it affects both how much radon enters the building and how efficiently the gas that has entered is removed. The optimal situation is achieved by combining structural sealing, controlled ventilation pressure balance, and, if necessary, targeted radon removal directly from the soil.
Remember: Only by measuring will you know. If concentrations exceed the reference values, corrective measures are usually straightforward and may qualify for a household deduction.
Home safety starts with clean and properly regulated indoor air. IVAeris Oy helps you ensure that radon-rich soil air does not enter your home due to uncontrolled negative pressure. Our experts will balance your ventilation system to operate efficiently and energy-efficiently, helping reduce radon entry and associated health risks. High-quality maintenance and correct adjustments are often the most cost-effective way to support healthy living. Request a quote for a ventilation inspection today!
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