LAS have been repairing American motorhomes for some 15 years now and have carried out a lot of repairs on motorhomes suffering from rainwater leaks. Many are from what seems to be windscreens and front caps, although several of these leaks have been caused by marker lamps and poorly sealed windscreens. Some of them have not actually been leaks at all.
One re-occurring problem happens on the early Winnebago Chieftain’s, the owners complain that they have water coming through the roof and into the rear wardrobe. Usually, this turns out not to be a water leak from the roof, but a problem that is caused by a process called thermal bridging.
Thermal Bridging
Thermal bridging explained in simple terms is where the warm air from inside your American motorhome tries to escape to the cold outside air. This process happens quite easily from places where little or no insulation exists. The point where the warm air escapes to the cold outside is known as a thermal bridge. This might not sound very important at the moment, you may think the easiest solution would be to keep the heating on, but this heat loss is not the only effect that a thermal bridge has. When the heat escapes to the outside air through the thermal bridge it caused water vapour, and this is why many owners of American motorhomes think they have a water leak.
Returning to the Winnebago Chieftain that I mentioned to you at the beginning of this case study, this vehicle has two aluminium channels in its roof construction. Between the roof outer skin and the aluminium channel, there is no insulation, therefore making an exceptionally good thermal bridge which fills with condensation. When the Winnebago American motorhome goes up a hill the condensation runs into the rear wardrobe, making it look like a water leak.
Image 2 above shows water dripping from an aluminium channel caused by a thermal bridge.
Due to the effects that a thermal bridge has, American motorhome owners can easily think that their windscreen or marker lamps are leaking. This problem develops when there is not any or very little insulation on the front cap, or when the insulation is not attached to the fibreglass, leaving a gap for the heat to escape and for condensation to form.
In image 3 above we can see the condensation has formed on the uninsulated front cap.
The use of fibreglass insulation is good but if the bond between the insulation fails, the fibreglass insulation absorbs the condensation and can start to smell and also corrodes the steel body supports.
In image 4 above you can see where the fibreglass has not been bonded to the American motorhome front cap, producing a very good THERMAL BRIDGE!
The answer and best solution that LAS have found is to use spray foam.
If you are thinking of selling up and going full timing then give LAS a call, so we can reduce this problem for you while you still have somewhere else to live.
