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Condensation on a Catering Trailer Roof: Is It Normal or a Leak?

by Adam
(Nottingham U.K. )

Grey catering trailer on a damp UK driveway with condensation on the roof

Grey catering trailer on a damp UK driveway with condensation on the roof

Hi,
I bought a trailer about a week ago and everything seemed fine. It’s a old trailer so I expected wear and tear. I’ve parked it up for a couple of days and when I went to it today I’ve noticed all the roof wet which appears to be condensation. Is this normal or do I have a leak somewhere? If I have a leak where do you suggest I start? It resembles condensation and no water seems to be on the floor or anything. Any suggestions?
Thank you

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Jun 29, 2026
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by: MobCater

Adam, what you're describing sounds far more like condensation than a leak, and that's the easier of the two to live with. The tell is exactly what you've noticed. Condensation shows up as an even film of water across the whole cold metal roof, it's worst after the trailer has been shut up for a day or two, and there's nothing pooling on the floor. A genuine leak behaves differently. You tend to get drips in one spot, brown tide marks or staining tracking down from a seam or a rivet, water on the floor below that point, and it gets noticeably worse after rain. Your water is spread across the roof with a dry floor, so that's the classic condensation pattern, especially in an older single-skin trailer.

What's happening is simple enough. The metal roof goes cold overnight, the warmer, damper air inside meets it, and that moisture turns back to water. Cooking makes it worse because frying and boiling throw out a lot of steam, and if you park up sealed tight with no airflow that damp has nowhere to escape.

The fix starts with ventilation, which is also the cheapest thing to try. Crack a roof vent or fit a small louvre so air can move through when the trailer is parked, and stick a couple of moisture absorber tubs inside while you get on top of it. For a longer term cure, insulating or cladding the underside of the roof with closed-cell foam board or an anti-condensation lining stops the metal getting cold enough to sweat in the first place, and a decent extractor over the cooking area earns its place every service.

One thing worth saying: that same ventilation matters for gas safety. If you run propane you need good airflow anyway so combustion gases clear and your flue stays unobstructed, so never seal the unit up airtight just to beat the damp. The two go hand in hand.

To rule a leak out completely, pick a dry day, get up top and check the seams, rivets and any roof fittings, then run a hose over it while someone watches from inside. If you spot staining tracking from one point, seal that properly rather than papering over it.

If it helps, the free MobCater app has a trailer setup and maintenance checklist that covers ventilation and damp alongside everything else, so you can tick things off as you go.

All the best

David

Disclaimer: This is general advice based on my own experience in UK mobile catering. Older trailers all behave a little differently, and if you ever find damp getting near your electrics or gas system, have a qualified engineer check it rather than risk it.

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