The 2015 revision of BRE Report BR 211, which includes guidance on radon protective measures for new buildings and conversions, contains an important section on basements and other occupied below-ground spaces.
The updated version recognises that the use of such areas is increasingly popular and that specific consideration must be given to how the structure will be protected from radon entry. This applies to domestic and non-domestic buildings.
Specialist waterproofing contractors are often employed to design and install the essential waterproofing elements of a basement conversion or creation, however methods of water management may conflict with gas management. It is vital that radon be taken into account in the design and installation of a waterproofing system and the following extracts from BR 211 provide an example of how this may be achieved.
Extracts from BR 211
6.12 Basements or occupied spaces below ground
It is important to ensure that basements and other occupied spaces below ground level are suitably protected against radon. These areas are more at risk because walls are in contact with the ground as well as the floor. For a house with a basement under the entire house, the area in contact with the ground could be several times that of a similar house without a basement. This, coupled with reduced natural ventilation below ground level, increases the risk of elevated radon levels. All basements are at increased risk of elevated levels of radon, regardless of geographic location.
Where a new basement is to be created, or an existing cellar converted, waterproofing will be required. A well-constructed waterproofing should be designed to protect against radon also. Guidance and recommendations on basement waterproofing are contained in BS 8102:2009, which also advises that radon be taken into account in the design and implementation of waterproofing schemes. Below-ground waterproofing and radon management are specialist activities that can conflict. It is recommended that dual protection systems are designed and installed by specialists who are suitably qualified in both waterproofing and radon management.
Internally located cavity drain membrane systems are often used to provide belowground waterproofing. Some cavity drain membrane systems are certificated as providing an effective barrier to radon gas. However, using these to line the internal surfaces of a basement could cause the gas to be simply displaced up the cavity into the ground floor accommodation. It is therefore important to ensure that the basement wall membrane fully closes the cavity at its head where it meets the radon barrier within the ground floor or external cavity wall above ground. The cavity behind the membrane could be used later as part of a subfloor depressurisation system.
If the ground around a basement is likely to be waterlogged, there is little benefit in installing a radon sump as subfloor depressurisation is unlikely to work continuously. As with all radon-protective measures installed during construction, the first aim should be to provide a passive solution. This should also be the aim with basement protection.
6.14.3 Non-domestic buildings
It is not a requirement of national building regulations to test new non-domestic buildings. Employers must ensure the health and safety of employees and others who have access to their work environment. An assessment of health and safety risks under national regulations should include radon where the workplace is in a radon affected area, or in any location where there is a basement that is regularly occupied. BRE recommends testing on completion or occupation all new buildings, extensions and conversions with protection fitted. Buildings that have had significant alterations made to them should also be tested.