In buildings
In most cases the most effective way of reducing radon is to install an extract system known as a 'radon sump'. The Building Research Establishment website shows some good examples of how radon can be reduced. Costs of installation vary but an average cost would be in the region of £500 to £800.
In new dwellings
Since 1991 certain precautions have been required against radon for new buildings and extensions. The level of protection required is detailed in the Building Research Establishment Report BR211, the latest edition of which was published in February 2000.
Maps in BR211 are used to determine whether or not protection is required and if so, what level of protection is needed.
Two levels of protection are specified. Basic protection consists of a radon-proof barrier which has to be incorporated across the footprint of the building. Full protection requires a radon sump in addition to the radon barrier.
Your local council building control officer will be able to advise you about the level of protection required in your area.