Regardless of where in the country a property is located, if it has a basement it is considered to be at ‘higher risk’ of containing elevated levels of radon. This is because a basement will have several surface areas in contact with the soil through which the gas can permeate, rather than the single footprint surface area that a property without a basement has. The atmospheric pressure within a basement is also usually low, meaning there is a greater ‘suction’ dynamic (advection) drawing gas from the soil into the property.
When carrying out radon testing in a property with a basement it is important to test the basement as well as the ground floor accommodation.
If high levels of radon are found in a property with a basement, a remediation contractor with specific experience of dealing with radon in basements should be consulted. One method of radon remediation is the creation of a radon sump beneath a building, which is a small void designed to collect radon so it can be safely vented away from the property. Unfortunately a basement is in itself a very large ‘sump’ beneath the building! This means that it is often not appropriate or possible to use a radon sump to reduce high radon levels in properties with basements, particularly as a sump will not be effective if it is waterlogged.
An approach using positive pressurisation, sometimes with the addition of a physical membrane, is usually required.
It is possible to combine a radon management system with certain types of basement waterproofing, so a basement can be converted into a dry and usable space that is safe to occupy. It should be remembered however that materials that are waterproof are not necessarily gas-proof, and therefore special consideration must be given to radon in any basement conversion project (the British Standard for below-ground waterproofing, BS8102:2009 requires this).
The UK Radon Association has members with specific expertise in this field and we recommend that you consult with them for further, practical advice.