New buildings must be planned in such a way that the average annual radon concentration in the occupied rooms is below 300 becquerels per cubic meter. To ensure this, a convection-tight design of components, connections and penetrations in contact with the ground is essential.

In most cases, high radon concentrations indoors can be avoided by sealing the building well against the ground. In certain areas, further measures (e.g. installation of radon drainage) may be necessary. This is particularly the case if a convection-tight design of the building components cannot be guaranteed or if the building site is located in a radon protection area.

Radon precautionary measures in Austria are regulated by the ÖNORM S 5280 Radon - Part 2: Structural precautions for buildings described.

This ÖNORM applies to the planning and construction of new buildings and extensions with habitable rooms (e.g. residential buildings, schools, kindergartens, workplaces). It can also be used for renovations in which horizontal components in contact with the ground are newly constructed down to the ground (foundation level) (e.g. installation of radon drainage).

A convection-tight design of the components in contact with the ground is fundamentally important. Structures that are sealed against non-pressing or pressing water and whose connections, terminations and penetrations are made convection-tight are in any case sufficiently tight against radon convection.

For the purposes of this ÖNORM, the following designs are convection-tight with regard to radon:

- Design according to ÖNORM B 3692 for the load case non-pressing or pressing water

- White tank" design in requirement class AS or A1

Execution of the continuous foundation slab with a thickness of at least 20 cm (concrete exposure class ≥ XC1), in combination with convection-tight pipe and cable penetrations and joint sealing tape or an equivalent measure when subdividing the foundation slab (vertically or horizontally).

The ÖNORM distinguishes between two types of precautions:

• Precautionary type A

When should this be used?

Precautionary type A is to be applied if the building site is located in a radon precautionary area, the components in contact with the ground are not designed to be convection-tight, the building has a full basement and no habitable rooms in contact with the ground are planned.

What measures must be taken?

The following sealing measures must be provided between the cellar and the area above:

- Installation of a self-closing, convection-inhibiting cellar door to the occupied area

- Sealing of openings through the cellar ceiling

- Sealing of ducts and shafts

• Precautionary type B

When should this be used?

Precautionary type B must be used if the building site is located in a radon protection area or in a radon precautionary area and the components in contact with the ground are not designed to be convection-tight. This precautionary type also applies if the building does not have a full basement and/or there are plans for rooms in contact with the ground.

What measures must be taken?

A radon drainage system must be installed in accordance with the specifications of ÖNORM S 5280 Radon - Part 2: Structural precautions for buildings. The radon drainage system creates a negative pressure below the building compared to the inside of the building. This prevents or greatly reduces convective radon ingress from the ground.