• David G Lenden

Do Radon maps give you the right route to Radon levels?


As someone with interest in Radon (or you probably wouldn't be reading this blog) you may well be aware of Radon maps.


The principle map that is often viewed, is the HPA (named as of production date, PHE as of todays date but soon to change again) Radon indicative maps (right). Which have become, almost, an abosolute "If it is coloured as a Radon Affected Area there's no need to bother". But that is not strictly the case. The PHE has clearly identified that the maps are "indicative" with the potential percentage of properties above the residential Action Level of 200 Bq/m3. When you read the associated text (actually an interesting read) you can see that the highest measured level in any grid square is the value allocated to the grid.


The data set PHE have access to and can be licensed from the British Geological Society is quite detailed. Reportedly with a implied accuracy of 1m! Buffers have been appplied to the levels (highest through to lowest), the geoloigical boundaries and the building location; resulting in a 75m boundary in total. These points are then plotted on maps producing somthing similar to the square right.


The data is then manipulated to group the data into 1km square with the colour that is identified for the highest radon potential. So the square above (right) would be presented as the square (right).

The HPA maps document (HPA-RPD-O33) states that 0-1% Radon potential contain no Radon Affected Areas and therefore "the atlas is definitive"; which is sort of true.


The maps are generated from NRPB/HPA measurements in residential properties across the UK . And they DO give a very good indication of the Radon potential. But the statement that they are "definitive" should be viewed with care.


Areas outside of the "Radon Affected Areas" identified on the maps, that is to say the white squares, do have a potential of, for example, 0.5%. Looking at the indicative maps the town of Taunton would be in the 0-1% potential (sample Left) surrounded by other significantly higher Radon potentials.



When the Built Up Areas are identified (also on a map (somersetintelligence.org.uk) and the no the irony is not lost on me) the area of Taunton is significantly built up.

If consideration is then taken of the popuation (as of 2018 (somersetintelligence.org.uk)) in Tauton of approximately 69000 with about 52000 households. If 0.5% of the households are actually being exposed to Radon levels above 200 Bq/m3 this would be around 26,000 households. So a significant number of peopel could potentially be at risk.

It would also be prudent to consider two more things.

  1. The 0 -1% Radon potential would lead employers to believe (incorrectly) there is "no Radon" (sic)

  2. No consideration has been taken of the risk to those living in or working in structures below ground level. PHE and the HSE both identify that such areas should be considered for measurement irrespective of the Radon potential map.

So using maps to determine Radon levels should be used with care.


How valid would mapping the highest value in a county be? It would centainly generate discussion and, hopefully, encourage people to measure at home and employees to comply with legislation.






Both PHE and the HSE have acknowledged that measuring one property does NOT tell you what the level is in an adjacent property. From our own measuring schedules we have found massively different levels between two homes in semi-detached houses.


The ONLY way to KNOW is to MEASURE


NEXT WEEK: Conveyancing with Radon.

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