Radon is everywhere, as a colourless, odourless radioactive gas formed by the radioactive decay of the small amounts of uranium that occur naturally in all rocks and soils. Radon is a risk to health as it emits radiation, that can cause damage to living tissue increasing the risk of cancer. Radon is linked to over 1,100 cases of lung cancer each year in the UK.
Surveyor Blog: Residential Radon
Exposure to radiation can come from natural and man-made sources. Radon comes from the ground. The underlying geology results to higher concentrations of Radon in some parts of the country. It is more common over rock types such as granite, shale and limestone or highly fissured formations. Higher radon levels give higher exposure.
The amount of radon is measured in becquerels per cubic metre of air (Bq m-3). The average level in UK homes is 20 Bq m-3. Radon accounts for half your exposure to radiation from all sources. For levels below 100 Bq m-3, your individual risk remains relatively low and should not be a cause for concern. However, the risk increases as the radon level increases.
The Action Level for Radon, above which it is recommended that mitigation work is carried out, is 200 Bq m-3.
The radioactive elements formed by the decay of Radon can be inhaled and enter our lungs. Inside the lungs, these elements continue to decay and emit radiation, most significantly, alpha particles. These are absorbed by the nearby tissue and cause localised damage which may lead to lung cancer. There is no consistent evidence that Radon causes cancers elsewhere in the body or other harm. The higher the Radon level, the longer the exposure, the greater the risk. The risk is also significantly higher if the person is a current or ex-smoker. At the Action Level, a current smoker has a 1 in 5 lifetime risk of lung cancer compared to 1 in 190 for a non-smoker.
Public Health England and the British Geological Survey have published Radon Affected Area maps for the whole of the United Kingdom, showing where high levels are more likely.
The darker the colour, the greater the chance of high Radon levels. The chance is one home in a hundred, in white areas, and one in three, in the darkest areas. It is possible for houses in the same street or even next to one another to have different levels of Radon. This is because Radon is a gas which seeps into residential homes by percolating through the rock following fissures.
A Radon Risk Report can be obtained to advise of the probability that a particular address or plot is above the Action Level (200 Bq m-3). However, a Radon Measurement Test will give the best guide to the level of Radon in a specific building. This is carried out over three months to allow for variations in levels. Small plastic detectors are placed in the home during this period. Radon levels in houses vary substantially from day to day as they are influenced by weather conditions. The amount of Radon also varies over time and from room to room in a home, so testing is carried out over three months to allow for variations in levels to average out short-term fluctuations. Tests that are carried out over shorter periods will have greater uncertainty and are more likely to lead to ambiguous and inconclusive results.
Where test results are above the Action Level, remedial work can and should be undertaken to reduce exposure. As the ground is the main source of radon, to be most effective, a combination of measures is likely to be necessary to draw Radon away or dilute levels in a building. Actions such as sealing around loft-hatches, sealing large openings in floors and extra ventilation will not reduce radon levels on their own. Completely sealing floors is difficult and can lead to collateral problems such as rot in wooden floors.
Additional measures can include:
Radon Sump: an active sump, fitted with a fan, is the most effective way to reduce indoor radon levels. Sumps work best under solid floors and under suspended floors if the ground is covered with concrete or a membrane. Passive sumps without a fan can also reduce radon levels.
Positive Ventilation: A small quiet fan blows fresh air, usually from the roof space, into the building creating positive pressure which pushes the gas out of the building.
Natural under-floor ventilation: many homes have a suspended ground floor with a space underneath. Good ventilation of this space can reduce radon concentrations.
Active under-floor ventilation: A fan is used to blow air into or extract air out from the space below a suspended floor. This is used when natural under-floor ventilation is inadequate to reduce radon levels.
Cellars and Basements: can be improved with a sump or positive ventilation.
Homes built since 2000 may already have radon protective measures installed and the Building Regulations 2010 state that ‘reasonable precautions shall be taken to avoid danger to health and safety caused by contaminants on or in the ground covered, or to be covered by the building and any land associated with the building’. The Building Research Establishment also provides information on areas where precautions against Radon are required under the Building Regulations for new dwellings and extensions.
New build properties in Radon Affected Areas are now expected to have Radon protective measures installed when they are built. The guidance recommends specific protective measures depending on the construction of the building and whether ‘Full’ or ‘Basic’ Radon protection should be provided. Basic protection is provided by a damp proof membrane modified and extended to form a Radon-proof barrier across the ground floor of the building. Full protection comprises a Radon-proof barrier across the ground floor and provision for a subfloor Radon sump or a ventilated subfloor void.
During the house buying and selling process, Local Search and Property Information Forms can be used to ask questions about Radon gas and advise whether records indicate that a property is in a Radon Affected Area. For “Buy-To-Let” property, Radon is one of the hazards specified in the Housing Health and Safety Rating System Regulations and an assessment may be required.
Some home buyers may arrange for a “Radon Bond” (typically £2,500) to be retained via their solicitor. This ensures that Radon testing does not hold up the property transaction. The bond money is initially held by one of the solicitors for a period of six months, to allow time for moving in, the three-month test, analysis and receipt of the report. If the result is below the Action Level, the money goes to the seller. If the result is higher, the money pays for remedial works and a timescale is agreed to allow for the works and a further test with any surplus money then going to the seller.
Surveyors can establish if a property is in a Radon Affected Area with an online search and this will advise of the chances that property could have a high level. For property in a Radon Affected Area, surveyors may want to ask sellers if they have recently completed a three-month Radon test and, if so, ask to see a copy of the report. If there is no report, it is prudent to consider additional action or recommendations.
Some lenders expect a comment to be made in the valuation report where a property is situated in an area identified as having a higher Radon risk. It is rare for the value or saleability of a property to be adversely affected or for there to be any market resistance to purchase, given the relatively low cost of mitigation works and also low public awareness of the issue.
A valuer would not normally request a specialist radon report as a condition of a mortgage valuation. However, when preparing a Home Buyer Report or Building Survey, investigations should be made to determine the likely level of risk from Radon and the matter reported where levels are likely to be above average. A suitable warning should be given and the client recommended to obtain further advice from UK Radon
Hugh Riley FRICS, Senior Regional Chartered Surveyor at SDL Surveying