Radon
The radon map is coloured for the postcode and no detector has been in this cellar. What has nobody measured?
Not this cellar. The map colour for the postcode, with no detector in the room, means nobody has measured the radon here. UKradon maps describe areas. They are not a reading taken under this floor. A home survey can note the map and can note that the cellar was seen. It cannot turn a colour into the concentration in that space. Until a detector has been placed in the cellar, the number you do not have is the radon in the cellar itself.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Map colour is easy to wave because it looks like an answer. It is an area indication, shared by many addresses, not a test of the air in this cellar. Cellars matter because they sit in the ground, and a result upstairs, if you even had one, would not automatically be the result below. Here you do not have a detector result at all. The survey has not measured the cellar, and the map has not measured it either.
Do not fill the gap with the Action Level or the Target Level as if those published levels were this house's reading. Those levels are thresholds for interpreting a measurement. They are not the measurement. If the cellar is the room you care about, the next step is a test in that cellar, not a darker printout of the same map. Ask the surveyor what they could see in the cellar, and keep that description separate from a radon figure nobody took.
What should you ask your surveyor?
- Did you see the cellar, and was any detector present?
- Are you relying on the postcode map rather than a reading in this room?
- What can you say about the cellar fabric that is not a radon result?
What are the typical next steps?
- Treat the map colour as an area indication only.
- Do not state a radon level for a cellar that had no detector.
- Place a test in the cellar if you need that room measured.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Does a strong map colour mean the cellar has failed a test?
No. Colour is not a test. Nobody has measured this cellar if no detector has been in it, and the postcode colour is not that reading.
Can the surveyor estimate the cellar level from the map?
No. The map does not measure the house, and the survey did not run a detector in the cellar, so there is no cellar result to quote.