Effect of building land and building materials

The original building land, backfill material brought to the site and gravel or aggregate material used in subsurface drainage systems all together affect the flow of radon-bearing air from the ground. High air permeability of the building land increases these currents. Therefore, the highest radon levels have been measured in houses built on moraine.

On more compact ground, layers of backfill, gravel or aggregate material increase air flow from the ground, due to their high air permeability. In addition, these materials themselves produce radon into the soil air. Thus, thick gravel filling layers can increase the indoor air radon level in a low-rise residential building on clayey soil above the maximum value of 200 Bq/m3.  Because of radon, it is not allowed to make compromises with regard to the quality of gravel used for subsurface drainage systems. The use of too fine soil leads to moisture problems.

A radon-safe foundation solution is the primary means for preventing the original soil and the gravel brought in from affecting radon concentration in indoor air. In very rare cases of exceptionally high known uranium content in soil, it is reasonable to consider not using soil brought to the site. In such a case, the overall effect of the original building land, backfill gravel and the chosen foundation on the efficiency of the radon-technical solution must be investigated. In areas with very high radon levels, such foundation solutions should be used that best enable ensuring a low radon concentration in indoor air.

The most significant factor affecting the radon level is the radon-containing air flow from the soil. Building materials have the strongest effect on the radon concentration in houses with a concrete frame. Walls, ceiling and floor made of concrete elements produce approximately a 70 Bq/m3 radon concentration in the dwelling. In wooden low-rise residential buildings with only the floor slab made of concrete, the contribution of the concrete material in the slab is less than 20 Bq/m3. Thus, in the light of these figures, a dwelling unit with a concrete structure requires stricter control of radon leakage from soil compared with wooden houses – both have the same radon concentration target level of 200 Bq/m3.

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