Radon
A radon sump was built into the extension slab and the fan is missing. What of the system is incomplete, and what level has not been measured?
The fan is the incomplete part, and no radon level has been measured in the extension. A sump in the slab is a void meant to collect soil gas so a fan can draw it away. With the fan missing, that extraction is not in place. The survey saw the sump arrangement and the absence of the fan. It did not test the air and it did not measure a radon level in the room. A map of radon risk is a different product and was not a reading taken here.
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?
A sump without a fan is a passive hole, not a working extract. Pipework may also be unfinished, capped or simply not seen, and this visit has not traced a complete run from the slab to an outside discharge. Soil gas does not announce itself by eye. Without a measurement, the survey cannot say the extension is high, low or ordinary. The missing fan is a visible gap in the system. The level remains unmeasured.
Ask the solicitor whether any radon report, fan specification or building-control note for the extension is in the papers. A radon specialist can test the air and can say whether the sump, the pipe and a fan need to be completed as one system. The survey has not done that test and has not decided that the house needs, or does not need, extract. Do not treat a map colour as a reading in this room.
What should you ask your surveyor?
- Is any pipe from the sump visible, or only the slab detail?
- Was a fan ever recorded on a drawing in the pack?
- What test would measure the level the survey has not measured?
What are the typical next steps?
- Ask the solicitor for any radon test or fan note for the extension.
- Commission a radon measurement rather than reading a map as if it were this room.
- Do not tell the lender a level was taken on this visit.
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 national radon map stand in for a reading in this extension?
No. A map is a separate product about area risk. It is not a measurement of the air over this slab, and this survey did not carry one out as a test of the room. The missing fan and the unmeasured level are findings about this house. A map colour does not complete the system or fill in the missing reading.
Can the fan be assumed to be stored in a cupboard?
No. The survey did not find a fan connected to the sump, and it has not assumed one is stored nearby. An unfitted fan, even if a box turned up later, would still leave the system incomplete on the day of the visit. Completion means the extract is installed and can run, which was not what was seen.