Damp readings in a caravan or motorhome: what the percentages mean
Sources checked 4 October 2026. They are listed at the end of this page.
On the damp report an Approved Workshop fills in, a reading of 0 to 15% is no cause for concern, 15 to 20% may need further investigation, 20 to 30% will need it, and 30% or more may mean structural damage is happening. Those bands are the guidance notes printed on the Approved Workshop Scheme's sample damp reports for touring caravans and for motorhomes. They are guidance notes, not a legal standard.
The four bands
| Moisture reading | What the report's guidance notes say |
|---|---|
| 0 to 15% | What the report's guidance notes say: No cause for concern. Only readings of over 15% are recorded. |
| 15 to 20% | What the report's guidance notes say: May require further investigation. Compare with average readings and consider a recheck after 3 months. |
| 20 to 30% | What the report's guidance notes say: Will require further investigations to look for other possible indications of water ingress. Possible resealing required. |
| 30% and above | What the report's guidance notes say: May indicate that structural damage or deterioration is occurring. Possible resealing required, followed by immediate rectification action as necessary. |
The Camping and Caravanning Club makes the same point about the lowest band: the readings will always be above zero, and anything up to 15 per cent is considered normal. For a reading above that, it says, your workshop can advise.
What a reading does not tell you
- It varies with the weather. The report says readings may be subject to atmospheric conditions, and it has spaces for the weather and the temperature on the day.
- It covers the inside only. Only the inside of the habitation unit is tested. The scheme says the underside and outside get a visual inspection, not a meter.
- It can miss what is behind your belongings. The report says personal belongings are not removed from lockers and storage areas, which may limit the scope of the test.
- It depends on the meter. The report records the make and model of the meter and whether its calibration was checked. The Camping and Caravanning Club says damp checking needs good quality equipment and expert analysis, and that simple DIY meters can be misleading.
- It depends on how the body is built. The scheme says that with newer construction methods and materials the testing a manufacturer requires may vary, and tells owners to ask the workshop about their own model.
How the readings are taken
The sample report notes that readings are taken at 300mm intervals. A damp check is part of the yearly service at an Approved Workshop, which is described in the habitation check guide.
Reading a report when you buy or sell
Ask for the whole report, not one number. Its comments and recommendations section is where the workshop writes what it found and what it advises. If you are selling, a recent report is something a buyer can read for themselves: the caravan and motorhome pages cover what else goes in the advert.
This page reports what the scheme and the club publish. It cannot tell you whether a particular caravan is sound; that takes a workshop with the vehicle in front of it.