Caravan Damp Checks and Habitation Servicing: What the Readings Mean

Damp & Servicing Guide

A practical guide from Bedam Leisure — caravan & motorhome specialists

There is one job that decides whether your van is worth anything in ten years' time, and it isn't the engine, the awning or the upholstery. It's the annual damp check. Water gets into a bonded sandwich panel quietly, does its damage invisibly, and only announces itself when the wall goes soft — by which point you're looking at a bill with a comma in it.

Late September is the moment to book. Workshop diaries fill from October onwards as everyone else lays their van up for winter, and by November you'll be offered a date in February. Book now and you also get the useful version of the appointment: any faults come back to you while the weather is still dry enough to fix them.

Habitation service or damp check — what's the difference?

People use the two terms interchangeably and they aren't the same thing. A damp check is exactly that: a technician takes moisture readings around the body and gives you a report. It's quick, it's cheap, and on its own it tells you nothing about whether your gas is safe.

A habitation service (often called a hab check) is the full inspection of everything that makes the van habitable, and the damp survey is one section of it. Expect roughly fifty separate checks: a manometer test for gas soundness, every gas appliance lit and run, the 12V and 230V systems including the RCD and the circuit breakers, water system and taps checked for leaks, waste outlets, the toilet seals and flush, ventilation clear at high and low level, smoke and carbon monoxide alarms tested, fire extinguisher and blanket in date, and the bodywork, doors, windows and roof inspected — with damp readings recorded throughout.

Note what a habitation service is not: it isn't a chassis service. On a caravan, the running gear, brakes and bearings are a separate job, and on a motorhome the base vehicle is serviced by a Fiat, Ford or Peugeot agent. Booking a hab check and assuming your brakes have been looked at is a common and expensive misunderstanding.

1 The damp check

What the numbers on the report actually mean

A technician uses a moisture meter with two pins, pressed through the wall covering into the panel behind it. The meter passes a small current between the pins and reports the resistance as a percentage. The reading is relative rather than an absolute measure of water content, which is why the pattern across the van matters as much as any single figure.

Most workshops work to broadly the same bands. Under 15% is normal and needs nothing. 15–20% is the caution zone — usually condensation or a seal starting to tire, worth noting and re-reading at the next service. Above 20% means water is getting in and something needs fixing now; by 30% and above you are likely looking at wet timber and delamination rather than a damp patch.

Keep every report. One reading in isolation tells you very little. Three years of reports showing the nearside front corner going 11%, then 14%, then 18% tells you exactly where your next job is — while it's still a tube of sealant rather than a new panel.

2 Your own inspection

The half hour that saves the appointment

You don't need a meter to catch most of this. Go into the van cold, first thing, before you've opened anything, and use your nose: a musty, cupboard-y smell is almost always the first sign of damp, and it appears long before anything is visible.

Then look at the inside corners, the wall below every window, and the ceiling around the rooflights. You're looking for dark staining, a blue-grey tide mark, or wallboard that has lifted slightly at a seam. Press gently with a thumb — sound board is firm, wet board gives. Walk the floor slowly and feel for anything spongy, particularly by the door and along the wheel arch.

Outside, run a finger along every sealant line: the awning rail, the roof-to-wall seam, each window frame, the rooflights, the number plate and light fittings, and every screw head on the body. What you're checking for is shrinkage — a hairline crack or a sealant bead that has pulled away at a corner. That's how water gets in, and it can be resealed in an hour by a workshop if you spot it now.

3 Parts that fail the check

The things that fail a hab check most often

Three-quarters of the advisories we hear about are small, cheap, and entirely predictable. Perished rubber around the habitation door is the classic one — it hardens, stops compressing, and lets in draughts and rain at the bottom hinge side. Window rubbers go the same way, chalky and shrunken, usually on the side that has faced the sun for ten years.

The other reliable failure is safety kit that has quietly expired. Carbon monoxide alarms are sealed units with a finite sensor life — typically seven or ten years from manufacture, printed on the back — and a technician will fail one that's out of date even if it still beeps when tested. The same goes for an extinguisher past its service date.

Test them properly. The button on an alarm only proves the sounder works, not the sensor. A DetectaGas CO Alarm Test Kit (£32.99) and DetectaSmoke test aerosol (£37.99) check the detection itself — the same way a workshop does it.

4 Over winter

Keeping the readings down until spring

A van that sits sealed and unheated from October to March will make its own moisture. Every litre that evaporates from a damp towel, a wet awning or the washroom has to condense somewhere, and it picks the coldest surface it can find — usually a window frame or the wall behind a locker. That's how a van with no leak at all still records rising readings.

The answer is airflow and absorption, not sealing it up tighter. Leave lockers and wardrobe doors open, lift the mattress or stand it on edge, never block the fixed vents, and put a moisture trap at each end of the van.

Covers help — if they breathe. A breathable cover keeps rain off the seals and UV off the sealant. A plastic tarpaulin traps moisture against the panels and makes damp worse. We've written separately on choosing the right cover, on stopping condensation over winter, and on the full winter layup.