Radon in new buildings

Radon prevention in the construction phase is easier and less expensive than implementing mitigation measures afterwards. Use of radon-safe building methods is justifiable anywhere in Finland. The goal is to achieve the lowest possible radon concentration.

The most common foundation type for low-rise residential buildings is a floor slab cast inside a footing. Between the slab and the footing, there is normally a gap through which radon can seep into the building. Using lightweight concrete blocks as the foundation wall material can make the situation worse. The same problem is met when lightweight concrete blocks are used as the material of walls in contact with soil in hillside houses or houses with a cellar, instead of cast concrete. Crawl space foundation, on the other hand, is a radon-safe solution, if radon is prevented from entering the house by sealing base floor joints and penetrations and ensuring sufficient ventilation of the crawl space. Monolithic slab foundation, relatively rare in Finnish low-rise residential buildings, is also a radon-safe solution. 

Efficient ventilation reduces the radon concentration in the house. With regard to radon, mechanical supply and exhaust ventilation is the best solution. According to building regulations, ventilation must always be adjusted to underpressure. In addition, the temperature difference between indoor and outdoor air increases underpressure at the floor level. This underpressure forces the radon-bearing air in the soil to flow into the house. The key question in radon control is the blocking or reduction of radon-bearing air flow from the soil.

Leakage routes of radon-bearing air
Leakage routes of radon-bearing air in slab-on-ground-foundation. Image: Symboli.fi

A radon-safe foundation is less expensive than the radon analysis of an individual site. Such an analysis does not usually guarantee that the radon concentration in indoor air will remain low, regardless of the building method. Values above the 200 Bq/m3 target value for new buildings are so common that radon-safe building methods are, as a rule, justifiable in the entire country.

In addition to reducing radon levels, radon-safe building methods can improve indoor air quality in other ways. A radon-safe solution prevents musty odours and any chemically hazardous gases from soil from seeping into the building.

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