What is Radon gas?
If you’re considering a basement conversion or basement build, what do you need to know? The information below has been prepared as a basic introduction to the subject only, with references provided to source data and further reading materials included under the ‘useful links’ page. Please read on and if you have any questions do not hesitate to contact us.
What is Radon?
Radon is a naturally occurring radioactive gas which is formed when uranium present within the earth and rock in minute quantities, decays. Radon which permeates through the ground into the open air is quickly diluted to low concentrations, however when rising into a building, greater concentrations can occur which represent a risk to health.
Why is it particularly significant in basements?
Radon originates from the ground. Structures above ground (without basements) have a single ground bearing substrate, this being at the base / floor construction. Basements differ, being surrounded by earth, with this bearing upon the walls as well as the floor construction and hence they are at greater risk of collecting radon gas from the ground.
One method of addressing radon in properties without basements is to include a radon barrier within the floor construction, and create a ventilated sump or chamber beneath to collect the gas. In this respect a basement is comparable to this sump, albeit on a larger scale.
I still don’t understand why basements are at greater risk…
Where basements are employed as habitable living space, consideration must be given to the inclusion of heating and ventilation, which is necessary to prevent water vapour from causing condensation (cooking/washing/cleaning/breathing i.e. occupation, all generates vapour).
Warm / heated air within an occupied basement, rising to storeys above exerts ‘suction’ (a physical force created by difference in pressure), on the basement space, which encourages advection, whereby air and other ground gases are drawn through the structure into the internal living space. This process as a result of warm air rising is known as the ‘stack effect’.
How much is too much?
Radon is measured in becquerels per cubic metre of air (Bq/m3) (Henri Becquerel discovered radioactivity in 1896). The health risk associated with radon is a function of the level/concentration of radon, and the length/extent of exposure.
Guidance on acceptable radon levels is provided by the Health Protection Agency (HPA – www.hpa.org.uk) a UK government quango set up in 2003 to advise on health issues including radiation, from medical to environmental sources.
Two significant levels of radon are defined, these being the ‘Action Level’ of 200 Bq/m3, and the ‘Target Level’, of 100 Bq/m3. Yes this is perhaps confusing, however it can be simplified by explaining the advice offered by HPA in differing circumstances:
• Radon levels are present, but below the target level of 100Bq/m3. While lower is always better (HPA state that there is no specific safe/unsafe threshold), in this circumstance the level is within that which the HPA advises homeowners should look to achieve.
• Radon is present between 100Bq/m3 and 200Bq/m3. HPA advises that homeowners should seriously consider reducing the radon level within the home, but can consider that the risks at this level are lower than in homes above 200Bq/m3 (the action level). Homeowners are also advised to consider that if they are within a higher risk category (smokers or ex-smokers) the risk of any radon level is much greater.
• Radon is present above 200Bq/m3. HPA advise that this require urgent action to reduce, setting the target of reduction to below the ‘Target Level’ of 100Bq/m3.
For comparison, the HPA ‘Limitation of Human Exposure to Radon’ report states that the average level of radon in homes is approx. 20Bq/m3, and the comparable value outdoors is approx. 4Bq/m3. It can range up to 10,000Bq/m3 plus.
On average for the UK population, radon accounts for 50% of our exposure to radiation.
Is every property affected by radon?
No, for property above ground the HPA publish maps produced in association with the British Geological Survey which show the estimated percentage of homes in an area above the radon action level (200Bq/m3 annual average), this being based on measurements taken in 460,000 homes.
The maps reveal whether property is located within a ‘Radon Affected Area’, which is defined as any location with a 1% probability or more of present or future homes being above the 200BQ/m3 ‘Action Level’. It is recommended by the HPA that homes within a ‘Radon Affected Area’ should have radon measurements undertaken.
Therefore, if for example your property is located within an area defined as having 0 – 1% percentage of homes at or above the action level, there is a probability that your property (above ground) will not be affected, but it should be noted that this does not mean ‘risk free’. HPA use the phrase ‘lower probability radon areas’, for < 1%.
What about property below ground, i.e. basements?
HPA have stated, ‘From data collected within workplaces, it is clear that basements have a higher radon potential than ground floors, and that radon can be found in basements anywhere in the country, regardless of Affected Area status’. Tracy Gooding, HPA, Environmental Radon Newsletter, Winter 2007.
Comment is also provided within the HPA ‘Limitation of Human Exposure to Radon’ report, to the effect of ‘The HPA recommends that householders in lower probability radon areas need not make measurements of radon concentrations in their homes unless they have a specific reason to suspect that occupants may be exposed to higher radon concentrations, such as in those homes which have underground rooms that are often occupied’.
Furthermore within workplaces, the Health & Safety Executive stipulates that under the 1974 Health & Safety at Work Act, ‘where employers must so far as is reasonably practical, ensure the health and safety of employees and others who have access to their work areas’, employers should, in occupied below ground space undertake and include radon measurements as part of the risk assessment. HSE states: ‘This applies to all below ground workplaces in the UK, irrespective of the above ground Affected Area status’.
While occupied basements are not present in all homes and workplaces, where these do exist, the advice is clear that consideration should be given to radon and its measurement.
Can I test for radon before I decide to have the basement converted?
You can, but HPA guidance on this (referring to unoccupied property generally – not basements specifically), is that the radon levels may change when the home is occupied, and that homes undergoing alteration also cannot be measured accurately, stating ‘it is best to wait until building work is complete and the home is again occupied in a normal manner’.
The basement conversion process is essentially designed to radically alter the nature of the environment within a basement, turning cold damp space into warm dry rooms, and hence it makes better sense to test the space post conversion.
Please note that further text will follow, please contact us if you should have any questions.