Retrofit radon remediation measures are usually carried out on existing structures when radon levels exceed the relevant action level. The action levels within the UK currently are 200bqm for domestic situations and the commercial action level is 300bqm as an annual average. There are many tried and tested techniques available for retrospective installations and our specialist contractors on the radon council contractor list will be able to provide you with all the options available.
The UKHSA state the following:- Radon levels can vary over time. This is usually because of changes to the construction of the building or alterations to heating and ventilation which can be caused by a change in use. For this reason, radon should remain in your routine reviews of risk assessments. Consider any changes and assess whether or not the test needs to be repeated. If a radon reduction system has been installed to reduce high levels, those systems may also fail over time and radon levels should be checked annually.