Damp in motorhomes and campervans, where it hides and how to check

Quick Summary:

• Damp is the single biggest threat to a motorhome's structural integrity and resale value, often causing invisible rot before it becomes visible.
• Key hotspots include window seals, rooflights, floor-to-wall joins, and external locker frames where seals can perish over time.
• A professional habitation check using a calibrated moisture meter is the only way to get a definitive moisture percentage reading.
• Never buy a vehicle with suspected damp without a professional damp report and a formal repair quote from an AWS-approved technician.

Damp is rarely just "a bit of moisture." In the UK's damp climate, it is a silent, progressive issue that can rot timber frames, delaminate panels, and significantly devalue your investment. Whether you are looking at a premium Frankia or a compact Vantage campervan, water ingress does not discriminate. The good news is that most damp issues can be identified early with a methodical inspection routine and the right tools.

Common Damp Hotspots: Where It Hides

Water follows the path of least resistance, often entering through apertures or where the body shell is pierced for accessories. Pay close attention to:

• Windows and Seals: Check for black spotting on the rubber and moisture trapped between double-glazing panes.
• Rooflights and Vents: These are high-stress points. Look for staining on the ceiling around the frames, particularly on models like the Bailey Autograph or Swift Carrera series where roof joints are critical.
• External Lockers and Seams: Any break in the outer skin is a risk. Check the internal corners of garage spaces and gas lockers.
• Rear Corners and Lower Panels: Road spray can be forced upwards into the floor ply if the underseal is compromised. This is common in older coachbuilt motorhomes like the Bessacarr E520.
• Awning Rails and Attachments: Screws used to mount rails or bike racks can provide a direct path for water if not properly sealed with non-setting mastic.
• Solar Panel and Aerial Entry Points: Aftermarket additions are frequent culprits if the cable entry glands have not been sealed with high-quality UV-resistant adhesive.

The DIY Sensory Inspection Checklist

While a damp meter is the gold standard, your senses are powerful diagnostic tools. Use this checklist during a viewing:

1. The Smell Test

A musty, earthy, or "mushroom-like" odour is a classic sign of advanced water ingress. Be wary of vehicles that have heavy air fresheners or "plug-ins" active during a viewing, as these may be masking smells. Open all cupboards to see if the smell is concentrated in one area.

2. The Touch Test

Run your hands over the wallboards. They should be firm and cool. If the wall feels "spongy," soft, or if the wallpaper/vinyl is bubbling or peeling, water is likely present behind the surface. Check the floor for "delamination"—a bouncy or creaky feeling where the layers of the floor sandwich have separated. This is a common check for older Swift or Auto-Trail Apache models.

3. The Visual Test

Look for "pitting" or small grey/black spots on the wallboards. Check inside high-level lockers and under bed bases, specifically where the wall meets the floor. Use a high-lumen torch to look into dark corners and behind furniture where air circulation is poor.

Ask for Evidence, Not Reassurance

A reputable seller should be transparent about the vehicle's history. Before committing, ask to see:

• Habitation Inspection History: Ideally, an annual report from an Approved Workshop Scheme (AWS) technician. This is vital for maintaining warranties on newer models like the Bailey Autograph 74 4.
• Damp Reports: A specific grid showing moisture percentages across the vehicle. Ensure the report is dated within the last 6 months.
• Repair Invoices: If damp was found and fixed, ensure the work carries a transferable warranty and was completed using correct sealants (e.g., Sikaflex or Soudal).
• Storage Habits: Was the vehicle stored under a breathable cover or in a dry barn during winter?

Damp Reading Reference Guide (2026 Standards)

Moisture meters measure the electrical conductivity between two points. Note that metal-clad vehicles or surface condensation can sometimes cause false positives.

Reading (%)	Status	Action Required
0% - 15%	Dry	No action; normal structural moisture levels.
15% - 20%	Warning	Monitor closely; re-check in 3 months. Possible early ingress or condensation.
20% - 30%	Active Damp	Remedial work required. Identify source of ingress immediately.
Over 30%	Structural Risk	Severe water ingress. Likely timber rot and structural degradation. Professional repair essential.

What to Do if You Find Damp

Finding damp does not always mean you should walk away, but it must change your strategy. Do not be swayed by claims that "it is just a small leak."

• Get a Professional Quote: Damp repairs are labour-intensive. Re-sealing a rail is relatively inexpensive; replacing a rotted structural timber frame can cost thousands.
• Adjust the Price: If you choose to proceed, the cost of repair plus a 20% contingency buffer should be deducted from the "clean" market value.
• Walk Away: If the damp is widespread or the seller is dismissive, there are plenty of dry used motorhomes for sale elsewhere.

Frequently Asked Questions

What is a "normal" damp meter reading?

Generally, 0-15% is considered dry. 15-20% is a "warning" zone requiring a re-check in 3 months. Anything over 20% suggests active ingress that needs remedial work. Note that some meters may read higher on cold days due to surface condensation.

Can I fix damp myself?

Minor re-sealing of external rails or replacing a window seal is a common DIY task. However, internal structural repair or replacing wallboards requires specialist tools and materials to ensure the vehicle remains safe and maintains its resale value.

Does an MOT check for damp?

No. An MOT only covers roadworthiness (brakes, lights, tyres). You need a specific Habitation Check to assess the living area for damp, gas safety, and electrical integrity.

How often should I check for damp?

In the UK climate, an annual habitation check is the minimum recommendation. However, performing a DIY check with a moisture meter after winter storage or heavy rainfall is good practice for early detection.

What to Do Next

• Browse campervans for sale and use these tips during your next viewing.
• Read our guide to Habitation Checks to understand the full inspection process.
• Check your potential vehicle's weight limits with our Motorhome Weight Checker.
• Explore Motorhome Models or Campervan Models to compare construction methods.
• If you are buying a caravan instead, use our Caravan Towing Calculator to ensure a safe match.