Converting American RV Motorhome Roofs from Aluminium to Fibreglass

Between 2001 and 2004 some of the American RV motorhome manufacturers moved away from the rubber roof membrane and started to cover the roofs with two sheets of aluminium in a quest to stop some of the leakage problems.  If you think about it this could have been a good solution to an escalating problem.

Aluminium can also be painted white to reflect the heat and will also eliminate the white streaks down the paintwork that you get when you don’t clean your rubber roof frequently.  As well as this aluminium is quite malleable, this enables manufacturers to profile the roof from the centre allowing the rain water to be led down gutters on either side of the motorhome.

One thing the manufacturers did overlook was the term we have talked about previously which is thermal bridging.  This is the process that happens when one side of a surface is cold whilst the other side is warmer.  To explain this easily think about your car windows on a cold day, the windows are clear until you warm the inside up slightly then moisture appears on them.

With the aluminium roof covering this thermal bridging becomes a rather large and expensive problem.  As the cold surroundings cool the outside of the aluminium then the lack of insulator causes moisture to form on the other side of the roof. This moisture then soaks into the wooden underside construction of the roof which evenly rots the roof members.  This thermal bridging process has been known to be that bad that owners have been convinced that they have had a rain water leak.

One answer to this problem would be to fully insulate the underside of the roof and bond the aluminium outer sheets to the wooden structure of the roof, this in many cases had not happened.

As time goes by these problems are now starting to show, and with good quality rear engine RV pushers hard to find, this makes a good repair viable.

At LAS motorhome we have started to look at this problem for a customer and have decided the best cause of action is to rebuild the roof and recover it with fibre glass.  First of all the roof needs to be completely stripped back.

Look at the pictures and you will be able to see the damage the thermal bridging effect has caused.

In image 1, we see a damp patch exposed by removing a piece of aluminium.

As seen in Image 2, from a distance the roof doesn’t look too bad when the aluminium has been removed.

In Image 3, take a closer look and you can see the problems.

In Image 4, we can once again see what the thermal bridging effect has done.  The condensation has formed on the underside of the aluminium and that condensation has soaked into the wood structure and in turn rotted the wood.

Image 5 shows the underwood covering is being removed which exposes the polystyrene insulation.

In Image 6, we can see a lot of damage was caused in the living area which backs up the thermal bridging theory, as that area would have been the warmest.

Shown in Image 7, after the aluminium has been removed the decision was made to remove the polystyrene insulation.

Image 8 shows the new insulation in place. It was covered then with sheets of plywood.

In Image 9 we can see all the plywood sheets are fitted, and the roof is now flat which is not how it was originally.

Image 10 shows the construction of the new roof profile.

As seen in Image 11, we have a profile as well as a potential problem with the space between the profile, a possible thermal bridging problem.

As you guessed with LAS the team have a very high skill level and we had already thought of that. In Image 12 you can see that holes have been drilled into the roof.  This is where we have injected insulation foam giving the roof a good insulation quality as well as making it a very rigid construction.

In Image 13, you can see the finished roof has no joins and has a profile identical to the original.  The new roof is far better than the original and now has greater insulation quality.

For comparison, Image 14 shows the old roof just before we removed the aluminium outer skin.

For more information contact LAS on 01604 861999.