With homeowners and businesses making the most of what they’ve got by converting cellars or creating new basements, Martin Freeman of leading waterproofing and radon specialists PropertECO gives valuable advice about how to avoid future risks and design liabilities
The stagnant, low-key property market has made moving a limited option for those wishing for increased living or working space. Stamp duty, the sheer cost of moving, lack of choice of property on the market and the increase in home working have contributed to the growth in newbuild basements and conversions. Specific design requirements for basements essentially include the need for them to be ‘light’ and ‘dry’, to which should now be added ‘healthy’.
The British Standard (BS 8102) is the code of practice for the protection of below ground 
structures against water from the ground. It provides appropriate guidance for basement waterproofing but crucially, since the most recent version was published in November 2009, it includes the need to take account of radon in the design and implementation of the work. Property professionals who do not take notice of this may be sleepwalking towards a time bomb of liability claims of their own making.
Radon is a naturally occurring gas produced during the decay of uranium, which is present in minute quantities in the ground beneath us. As radon is a gas, it can escape from the ground and accumulate in 
buildings. Long-term exposure to elevated levels of radon can lead to lung cancer, and current statistics estimate that in the UK over 2000 lung cancer deaths every year are attributable to radon exposure.
To an extent, the underlying geology impacts upon the amount of radon in a given location and there are maps available to indicate the likelihood of high levels being found in particular geographic regions. These maps are not definitive and there are many instances where high levels of radon have been found in areas not designated as at risk by the maps.
Radon enters buildings via the process of advection, which is the movement of a gas from a point of high pressure to a point of lower pressure. In other words, gas in the soil beneath a building is actively “sucked” into the building. The greater this pressure difference, the greater the rate at which gas from the soil is drawn inside.
Cellars and basements are particularly at risk from radon, regardless of their geographic location. Firstly, they have a number of surfaces in communication with the ground, which increases the sources of entry for the gas. Secondly, a basement will naturally have low pressure and will therefore draw radon from the surrounding area towards it. The Health Protection Agency advises that “From data collected in workplaces it is clear that high radon concentrations can be found in basements anywhere in the country, regardless of Affected Area status” [i]. This stance is also adopted by the Health & Safety Executive (HSE) who not only require employers with workplaces in Affected Areas to carry out a radon risks assessment but also all those whose premises have a basement anywhere in the country.
Whilst radon testing in existing properties is possible and advisable, it is not appropriate to test a redundant cellar that is due to be converted into habitable accommodation as the radon level before and after the works is likely to be significantly different. Sealing draughts, installing insulation and using heating all have the potential to increase radon levels within the finished basement, therefore whilst a test carried out in a draughty former coal-hole might show low levels of radon, the levels in the finished room may be much higher.
Similarly, where a new basement is to be created, either via digging out under an existing property / garden or as part of a whole new building, it is not possible to test the ground to assess whether radon will or will not be present in the finished basement.
The British Standard for waterproofing requires designers to assume that even if the cellar is not currently wet, there is a good chance that water may come to bear at some point in the future and therefore appropriate protection from this should be built into the design. This same presumption should also be made about radon gas.
Protecting a cellar from radon intrusion can be very difficult and, if not designed correctly, can lead to increased radon levels not only within the basement but also in the accommodation above.
The current best practice, and most commonly used, method of waterproofing is Type C drained cavity membrane systems. These are highly effective and reliable for waterproofing, however the very theory that makes them so effective is in direct conflict with the management of gas intrusion.
Cavity drain membranes are dimpled sheets of HDPE that work by providing an air gap between the internal face of the wall and the front of the membrane. This allows moisture to penetrate the basement walls and then fall down behind the membrane into a drainage channel. Other than at the baseline, the membrane does not need to be perfectly jointed or sealed to work, as the water penetrating the walls will depressurise when it enters the air gap due to the lower pressure here. Unfortunately, as described above, this is conducive to enhancing the draw of radon towards the basement.
As the membrane joints cannot be expected to remain gas tight over time, radon would be free to pass through these joints into the basement. Similarly, as the head of the membrane is not usually sealed a pathway for gas is readily available behind the membrane up to the ground floor accommodation, potentially raising radon levels throughout the entire building.
Other forms of waterproofing such as externally applied adhesive membranes or cementitious coatings are also inappropriate. A landmark ruling in 1999 (Outwing Construction v Thomas Weatherald Ltd) found, among other things, that external membranes were undesirable as they required perfect workmanship, which is unlikely to occur under building site conditions, and they were not repairable should a defect occur. For the same reasons, they should not be considered suitable for gas protection.
Cementitious coatings have also fallen out of favour with designers as they often crack or debond after time, leading to leaks and flooding.
Whilst a flooded basement is likely to cause severe decorative spoiling and upset to the owners, the ‘upside’ is that the problem can at least be seen. In the case of radon permeating into the basement, it cannot be seen or smelt therefore unless occupants carry out testing they will be unaware that the gas could be entering and accumulating in the property. The results of this could be far more devastating than the damage to property that a flood could cause, yet many designers and installers continue to overlook the issue.
It is true to say that although awareness of radon amongst professionals and the general public has increased during the last few years, many are still oblivious to the risks. Professionals responsible for the design or implementation of works to a property have a responsibility however to ensure that they are up to date with current guidance and legislation and have a duty of care towards their clients.
With increased awareness about the risks associated with radon, it is less likely these days that the problem will go unnoticed. In property transactions, there is a standard enquiry before contracts about radon; surveyors, valuers, lawyers and buyers are more widely aware that basements everywhere are considered at risk and may require a radon test. If the property is a workplace, the employer has a duty to test for radon if there is a basement. So it’s now more likely that a basement conversion that hasn’t taken account of radon will be found out and the recriminations will begin.
Some specialists involved in the basement waterproofing industry have made attempts to include radon protection into their designs, however there are known instances where the methods recommended or even installed have increase, or have the potential to increase, radon to dangerous levels within clients properties. For example, the radon level in a cellar in a domestic property in the Cotswolds was inadvertently doubled when the workman installed an extract fan thinking that this would rid the basement of radon. In fact, this did the opposite and simply served to draw more gas into the basement from the surrounding soil.
Further care must be taken to avoid placing reliance on materials claimed to be ‘radon proof’. Whilst it may be the case that sheets of membranes and tapes have been tested for permeability in a laboratory, it is the installation of these components combined which can lead to radon entry as the fixings will not be gas tight, the joints over time will not remain gas tight and the membrane may form a pathway for gas to travel to other areas of the building.
Using the right techniques, it is perfectly possible to create a basement that is both dry and healthy. The necessary expertise is required to take account of all likely radon sources, dynamics of entry and configuration of the accommodation prior to designing a system that should include a combination of physical barriers and active air management. It is vital that consideration is given to where the displaced gas will be diverted to, to ensure that this is safely away from the rest of the accommodation.
Upon completion of any scheme involving a basement, radon testing should be carried out to confirm that neither the basement nor other areas of the property are affected by elevated levels of radon. If the designers cannot show that they have taken appropriate steps to protect the property from radon intrusion, it will be the designers who are liable for this defect.
Some three years after the publication of the revised British Standard, it is time that those involved in the design, construction or conversion of basements ensure that they are designing and installing appropriate systems that will not have the potential to endanger their clients’ health. If they do not and high radon levels are subsequently discovered in the property, they must be held accountable.
The World Health Organisation (WHO)’s Radon Handbook places clear responsibility for radon risks on architects and builders and other property professionals, clarifies that indoor radon concentrations are not naturally occurring rather they are “profoundly influenced by the way homes are designed and built”.[ii] This statement provides clients with the ammunition they require to bring action against a designer or contractor who has failed to take account of radon. In order to succeed, the client would not need to develop lung cancer as a result, but purely provide evidence that a potentially dangerous basement has been created.
After all, no client would accept a new basement that was damp or had water leaking in, so why would a client accept one that is being permeated by radioactive gas that could damage their health?
Martin Freeman is Managing Director of Bath-based propertECO.
Martin has over 40 years’ practical & technical experience in the building preservation 
industry and, in addition to working in senior management roles at several regional and national contracting firms, Martin has owned a laboratory consultancy specialising in the resolution of disputes involving problems of dampness in buildings.
Martin has also been at the forefront of the radon industry since the early 1990s, when he was the initiator of the industry technical and self-regulatory body, The Radon Council, of which he is currently Technical Affairs Spokesman.
Having a strong personal interest in radon, he has fought for many years for the hazard to receive more attention amongst Government, professionals and the general public. He has been invited to international conferences on the subject, and has been involved in
consultations with some of the world’s leading specialists in the field.
His combined experience in waterproofing and radon management field is unrivalled, and he has an international client base to show for it.
