Call us now on 01604 861 999

Roofing

There are 3 main roof constructions which are found on American Motorhomes. The first roofs that were built in the 1980-1990’s were a wooden construction, consisting mostly of one full length piece of oriental strand board (OSB) covered over with an aluminium sheet and sealed edges. This roof proved sturdy, and yielded few problems, however there are still some drawbacks which need to be mentioned. The most common problem we have found is the roof vent sealer becoming weakened due to age, letting water through to rot the wood and causing considerable damage to the roof structure. A further problem with this type of roof is the amount of noise generated when it is raining with the water hitting the aluminium sheets. Unfortunately however, this problem cannot be fixed other than by using a different roof construction.

The second type of roof uses the same main features of the wooden roof, with a full length; full width piece of oriental strand board (OSB) but in place of the aluminium sheets there is instead a rubber membrane bonded to the OSB board to make it watertight. This roof was popular during the 1990’s, being preferred to the wooden roofs as there is a noticeable difference in the noise level during rain. The rubber membrane has a damping effect, which makes the noise a vast amount quieter. Whilst being preferred to a wooden roof, this roof is not without its disadvantages; namely the rubber membrane. Being made of rubber, it is susceptible to the heat of the sun, causing cracks and causing the glue to fail, as well as being very easy to tear. These faults all lead to the same problem: water leakage through the roof. Once the water reaches the OSB underneath the rubber membrane, it picks up particles off the surface, dries, and turns into dust underneath the membrane. This causes the roof to lose a considerable amount of its strength and rigidity. From past experience we can say that it takes a large amount of care to keep this type of roof in good condition, and here are some tips we’ve learnt over the years:

• Wash the roof regularly to remove any tree sap, as this eats away at the rubber.
• Check the seals around the roof vents and if they are not in good condition reseal as soon as possible.
• Use a rubber roof protector if possible to protect the membrane.
• Use the correct sealers, as petroleum based sealers will melt the membrane and silicon sealers will not adhere correctly.
• Try not to walk across it too often.

If the membrane becomes faulty, the OSB underneath will follow suit in a very short period of time. The replacing process is fairly complex, beginning with the removal of both the membrane and OSB, and replacing the OSB with exterior ply. After bonding this to the polystyrene insulation, the air conditioning, fridge and roof vent apertures have to be cut out. Following this, the roof membrane can be glued to the ply and the side cappings, roof vents and air con units can be refitted and sealed. Obviously, this can be very labour intensive and a costly process, so it is worth taking the time and effort to look after the roof.

The third type of roof was introduced due to the faults and problems reported with the previous two. This roof uses exterior ply for the base, with fibreglass topping over it. The fibreglass can be applied in one of 2 ways; either a sheet for the entire roof, or 2 panels used vertically across.

To use the Winnebago Adventurer as an example, the roof was manufactured separately. It is built from a bottom layer of ply, much like our third roof construction, followed by a polystyrene insulator and a second layer of ply. The interior roof covering is applied to the bottom layer of ply before it is placed on the main body. This large piece of roof is then placed over the sides and back of the bodywork and then screwed into place. Finally, the fibreglass topping is slotted into some of the side cappings and bonded to the top layer of ply to give the rounded sides. Some manufacturers construct this roof by building the roof straight onto the vehicle however. This does not give the accuracy that building the roof separately does though, as a jig can be used for aligning the sides and roof. Despite this, when the roof is built on the vehicle, there are more variances available. If the fibreglass sheet is laid in 2 pieces, the alignment can be compensated by using a tape joint in the centre for example.

All things considered, the fibreglass roof is by far the better product out of these three, as it is superior in almost every way. Damage can be easily rectified with resin and matting, yet the noise level is almost the same as that of the aluminium roof mentioned before.

For more information, call us now on 01604 861 999