"Don’t forget what is at stake here," said John Sparks, Radon Council Board Member and co-author of the revised BR211 speaking about new procedures and processes in the revised guidance.
Radon is a naturally occurring element. It is an inert noble gas - soluble, colourless, odourless and tasteless - and is the densest gas known. It permeates through soil and into buildings, and the decay through half-life is 3.825 days. It can’t get through paper, but when the alpha particles enter the body, radiological biological evidence suggests that cells exposed in a single particle can become appreciably damaged.
With increasing environmental awareness and better energy efficiency in homes, increasingly stack effects are seen in buildings. Gavin Gillmore, professor emeritus at Bath Spa University and director and chairman of the Radon Council, explained there are lots of potential entry points for radon gas, including cracks in the foundations, water supply floor drains, porous blocks and as heat rises, it draws more gas in.
Two buildings next to each other can have very different radon levels and radon varies through time - peaking at night – when there is less air circulation. There are several variables with regards to radon penetration including geology, weather, building style and use, and climate change.
Mapping is key
A key to radon protection is having up to date maps with the latest data. Russell Lawley, geoscientist at the British Geological Survey, worked on the Updated Indicative Atlas for Radon in Great Britain. He said that radon is becoming more known in terms of the house purchase procedures, but outlined that there’s a perception that it is predominantly a Cornish problem with granite. However, there are issues with mudstone, limestone, sandstone, oolites, Northampton Sands and later chalk formations which show elevated radon. Areas of Wales, the Midlands and North are also affected.
Lawley noted that laws and regulations mention radon and the new UK Radon Action Plan increases awareness.
The new version of the map, linked to BR:211, was released in December 2022 and was an update of the previous version from 2007. It is based on a source-pathway-receptor model and synthesises 10,000 combinations of geological materials and 560,000 in-dwelling measurements. "It’s high content but clustered," says Lawley. "It is modelled to 1km2 and defined as a pessimistic model."
The Radon Potential map is 1:50,000 scale and shows the probability of the radon level. It is licensable from BGS.
Lawley explains: "Between 2007-2017 there were a lot of updates. The new map has an extra 80,000 sample points – and faster computing enables us to revisit the methodology - a new hierarchical statistical approach. We could rethink statistics, streamline methodology criteria and look at how radon is applied. Now we don’t have to rely on one individual."
In 2007 there were 479,000 samples, with a single layer of geology; now there are 560,740 samples with 4 layers of geology with improved statistics.
There has been a 23% change in the map. Areas where measures were required from no measures rose 4% and problems were detected in new areas.
In terms of current direction, Lawley said it is about communicating about radon, supporting stakeholders with new maps and research on radon in groundwater, soils and mining fracture flows.
Mike Jaggs, associate director and principal trainer at the Building Research Establishment, said radon can enter buildings through basement walls, raised flooring gaps, cracks and service entry points. With the stack effect and increasing energy efficiency, there is increasing reliance on membranes, quality of construction, sealing and ventilation.
Changing construction methods and defects in membranes were both contributing factors for a new BR:211.
Jaggs said that Part C explains what basic or full radon protection is. Basic protection in England and Wales should come into effect with any building risk between 3-10%; anything over 10% requires full radon protection. Basic protection also involves a continuous membrane covering the footprint of the building, with adequate sealing and the membrane inspected before follow-on trades.
National Building Regulations require protection against moisture – a membrane must be sealed to the damp proof. Jaggs stresses that a 300 micron polyethylene sheet is adequate for damp proof protection but BS 485:2015 A1:2019 states that a polythene membrane less than 400 microns or above is unlikely to withstand construction damage.
He says correct sealant materials must be used, and installation must occur in the right conditions, avoiding wet, cold and dust. The membrane must be checked before follow-on trades come in and third-party inspection is advised with an accredited NVQ inspector.
‘Full Protection’ requires all the previous with the addition of a sump and ventilated flooring. Any ground slab edges have to be supported and reinforced to stop settlement around the edges to avoid tears in the membrane. A radon sump has to be installed as a precaution, but it doesn’t need to be activated. The reach is around 15m. Jaggs says a good level of air flow around the sump has to be ensured with permeable fill. It needs to be capped off and labelled with an access plug accessible, and Sumps can be pooled together in bigger buildings.
Extensions and garages need to be protected. There is no requirement for a radon test on completion – only when it is occupied - but employers do need to test. If the test is above the action level, remedial measures should be applied.
BR:211 Design and Application
Peter Atchison, director at PA Geotechnical, Radon Council member and co-author of the revised BR211, outlined that the mapping and methodologies of construction have changed. Talking on Design and Application, he said: "BR211 wasn’t being sufficiently well used."
In 2015 the checklist was hidden away at the back, and it was easy to tick yes. Now it has been spread across the document as a Quality Management Record. In the new document, it is seen at each stage, and responsibility apportioned as the process progresses. There is an expectation that records are kept of decisions. The documents allocate responsibility to the designer, client and construction design team.
In 2015 there were a lot of basic block drawings. Now architectural standard details have been added. "The location of the radon barrier should be made in conjunction with the building design. Continuity of the barrier across the building has to be ensured. With full radon protection the location of sumps with exhaust outlets and liaison with building control is advised", noted Atchison.
The location of the radon barrier should be made in conjunction with building design (section 5), and continuity of the barrier across the footprint of the building should be ensured. With full radon protection, the location of sumps and exhaust outlets or underfloor vents should be identified. "The key is liaising with building control. Responsibility is with the designer."
Specification is challenging, according to Atchison: "To ensure the document was not compromised, lessons learned elsewhere in Ground Gas Management were identified. We didn’t want the document to become prescriptive as this dates it."
In 2015 the recommendation was for 1200-gauge continuous membranes which were accepted in damp proofing. In the latest version (6.2.1 on Barriers) the advice is to install 400 micron barriers which last longer. "Experience from other ground gas areas and BS8465 has been utilised."
With regards to permeability, there’s a danger of only testing one parameter, said Atchison. "Manufacturers are good at improving just one aspect of their materials against a perceived standard level and ignore other potentially important aspects of performance. BR211 is not designed as a performance specification. Thickness is guidance. Design is left to site specific choice by the designer. Radon resistance contributes to the decision-making process."
On specification, Atchison advises checking with manufacturers and suppliers that components, materials and sealants are compatible with each other and suitable for use as a radon barrier. "Consider using accredited installers and determine the inspection regime and on-site quality management. The design specification is important and sets out expected procedures and processes and is the responsibility of the designer."
Pointing out key points in the new document, Atchison advised "consider materials that are compatible and suitable. Consider accredited installers and determine inspection and on-site quality management at an early stage. Expected procedure and processes – responsibility of the designer. Also consider buildability and order of construction and inspection necessary to achieve continuous barrier." Atchison stressed this is the responsibility of both the designer and construction and design team.
"Make sure the sequencing is continuous – which means collaboration during each handover process with Building Safety Regulation advice."
For schedule of work and pre-inspection planning, a risk-based approach is recommended. Via pre-inspection planning consider various elements that could affect the installation and performance of the radon protection system, including the complexity of the installation, the competency of the team and influences of the follow-on team.
On procurement of materials and installers, the advice is to ensure materials purchased match the requirements set in the project specification. The responsibility is with the contractor/inspector. "Match the specification and use accredited installers."
On the weather, BR:211 says – avoid installation in cold or wet weather, minimise the time the barrier is exposed, and weather conditions should be recorded.
On barriers through walls, it advises making sure all elements work together. Cavity trays should be installed with an adequate step to prevent damp penetration. All joints should be sealed, and an installation inspection record required.
Quality of construction and inspection, testing and reporting
John Sparks, global operations director at GeoShield, Radon Council Board Member and co-author of the revised BR211, looked at the Section: Quality of construction and inspection, testing and reporting.
Sparks outlined the first paragraph: "To be successful, radon protection measures need to be implemented consistently throughout the construction process from design to handover, and the Radon Protective Measure Quality Management Record should be correctly followed and completed to ensure contractual responsibility for each process is allocated accordingly."
The 2015 document requested a critical path of the construction process to be recorded. Sparks said this was not being used and was rarely completed. "The checklist was at the back of 49 pages of maps. The result was no official record of the process from conception to completion and no allocation of contractual responsibility. If anything had gone wrong – there was no traceable evidence of what had happened."
Sparks said there needed to be a substantial change of emphasis. Now there is a totally new Section 7 - Quality of construction and inspection, testing and reporting. The document makes clear that the Radon Protective Measures Quality Management Record is a record not a checklist. "It is a record in chronological order – for the clients."
Sparks said that the main contractor, architect, design engineer, specialist applicator, verification organisation plus any other party on performance should be made aware of everything and at what stage in the process. Drawings need to be recorded, along with adverse weather conditions, damp proofing, sumps and vents.
And Sparks warns: "watch for the contractor breaking the specification. If it is altered – someone needs to agree and record it."
Construction methods have changed since the last version. New materials and installation techniques have come onto the market. The risk associated with radon gas has become more focused, so the delivery of solutions needed improving – hence the changes to BR:211 with responsibilities for design, implementation and inspection both emphasised and clarified.
Upcoming event: Radon Mapping in the UK
We're holding an online panel discussion on 29 January at 10:30-12:00 GMT, which will explore Radon Mapping in the UK. View the agenda and register here.