Installation of radon piping

The ventilation system of the foundation ensures control of radon concentration in indoor air, in case there are air leaks remaining in the base floor structures. The purpose of the ventilation system is to ventilate the soil air in the sub-surface drainage layer and to create underpressure in the foundation. Then the amount of air flowing into the house and the radon concentration decrease.

Typically, passive radon piping reduces the radon concentration by 20 to 60 per cent (Arvela et al. 2010). Therefore, it is important to lead the end of the exhaust duct above the roof already during the construction phase, keeping the end open. This also helps to avoid the need for alterations in the completed building, which would be the case if the exhaust pipe was installed afterwards. The radon level-reducing effect of the passive piping is based on ventilation taking place in the piping. It is induced by the temperature difference between the soil and outdoor air and the effect of wind.

When the building is completed, a control radon measurement is conducted. In order to obtain a reliable result, heating and ventilation systems must be completed and in normal use. If the radon concentration exceeds 200 Bq /m3 despite the prevention measures, an exhaust fan is installed in the exhaust duct. The simplest solution is to use a ready-made extractor fan that is connected to the exhaust duct. The RT reference card gives more detailed instructions on the dimensioning of the exhaust fan and air flow. Connecting a fan to the radon piping typically reduces the radon concentration by 60 to 95 per cent.

Furthermore, radon piping has advantageous moisture-related effects. Ventilation caused by the piping removes moisture from soil material located under the slab and near ground-supported walls.

The installation of radon piping should be in compliance with the solutions presented in the RT reference card. Other solutions may lead to an unsatisfactory result. The suction ductwork may be designed as looped or branched. The piping is located at least 200 mm below thermal insulation. This increases the underpressure achieved in the ductwork, and radon-bearing air is not sucked into the suction duct through the thermal insulation. The ventilation system can be implemented using the available construction and ventilation equipment. There is also a radon piping package available on the market that is suitable for low-rise residential buildings. It includes all the necessary pipes, connectors and accessories.

Installation of sub-slab radon piping

Installation of sub-slab radon piping Figure from the RT reference card (RT 81-11099).

Explanations:

1. Suction ductwork, plastic underdrainage pipe
- distance from foundation wall approximately 1.5m
- minimum distance from building elements that penetrate slab 0.5m

2. Transfer duct and exhaust duct, plastic underdrainage pipe

3. If the suction duct passes areas narrower than 3 metres, more leak-tight pipe material should be used in that area, such as stormwater drain pipe.

4. If the frame depth of the building is from three to four metres, a looped suction duct can be replaced with a single longitudinal suction duct with a blocked end. 

5. If the frame depth is more than 10 metres, an additional suction duct is needed, placed along the centre line of the building.

6. At the foundation penetration, the suction duct is replaced with a leak-tight pipe.

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