Structural differences between PVC & coachbuilt MHs

[TheMobileWanderer]

Hi Funsters,



I've just been reading several threads generally, via google (i.e. not here), about PVC & coachbuilt vehicles regarding the difference in their structures.



Some people say that a PVC vehicle is a PVC construction with insulation foam (PET), sandwiched between two sheets of PVC.

I thought in this context, PVC simply means 'panel van conversion'.



Anyhow, the structure of the PVC was explained but not that of the coachbuilt variety.



So, given that I am planning the build of a MH, with the best possible structure my question is:-



QUESTION: what is the normal structure of the roof, walls and floor of a coachbuilt motorhome?



As for my build; I have considered GRP outside with 40mm - 50mm foam sandwiched between that GRP and an internal (BS standard) marine plywood.

I have set a brief so I can try to follow it.

In case it is of interest to others here it is.



When finished:-

1. The outside should have the appearance of any other high-end motorhome.

2. The roof should not sag, regardless of any reasonable weight on it.

That could be two maintenance operatives in addition to the panels and other normal MH equipment, to be seen on roofs.

The roof should have additional insulation (over the amount in the walls), due to the fact that heat rises.

The roof should be able to cope with various ceiling trims being screwed bolted or stuck to it.

The overall thickness must be within the tolerances of skylights and other roof fittings' maximums.



3. The walls should have enough insulation to resist heat transfer both, to maintain heat and to repel hot summer sun.

The walls should be of sufficient structural integrity, to accommodate the weight of wall cupboards and other items screwed, bolted or sikaflexed to it.

The walls should be no thicker than the maximum set out in the windows and habitation doors' specification.



4. The floor should be robust to prevent road debris from damaging it.

It should also have sufficient insulation properties and a suitable surface to cope with wear and tear.

It should also be able to facilitate/support the installation of hatches for extra storage and underfloor access.



So, the materials I am considering are:- (numbered, relatively, to the points above)

1. GRP or other composite furface with or without gel-coat.



2. The roof to comprise three layers:-

a. 50mm PET sandwiched between GRP.

b. Alloy 'joists', running across the roof, bolted through that 50mm foam, into the alloy frame that runs along the side of the roof.

(That may require sleeving on the bolts, to prevent the crushing of 50mm foam board).

c. A further 50mm foam insulation sheeting, sculpted around the joists, such that there's minimal gap between both sheets of foam.

d. 15mm marine plywood (to BS standard) bolted through that inner 50mm foam insulation board into the joists. This also may require sleeving.





3. The walls shall comprise two layers

a. 50mm PET sandwiched between GRP

b. 18mm marine Plywood (to BS standard)



4. The floor shall comprise several layers:-

a. An aluminium base layer

b. 50mm PET sheeting

c. further PET foam sheeting of 20mm(to accommodate channelling for underfloor heating),

d. 18mm marine plywood to BS standard.

(the 20mm insulation foam will enable mistakes to be made, without wrecking the main 50mm under-floor insulation).

(The marine playwood at 18mm should be adequate to support hatches for underfloor access).

 

[funflair]

If you are going coachbuilt which by your description I think you are it would be worth having a look at how the likes of MORELO or Concorde build their box, the walls and roof are 1.4mm alloy bonded to a closed cell PU or EPX foam core, have look at this thread and watch a couple of the videos at the start.

How they build a MORELO

I think this is interesting even if you don't speak German, which of course I don't. Martin

www.motorhomefun.co.uk

 

[Kannon Fodda]

PVC at least in the context of Motorhomefun means a conversion if a panel van. Typically a courier's / builders van like the Ducato, Transit. The metal outer shell of the vehicle is largely intact, apart from perhaps holes cut for added rooflights or living area windows. The habitation stuff such as bed, toilet and cooker is all fitted out inside c including wall and ceilings affixed to the original metal frame.

PVC can also be used to describe a plastic material.

What is being considered here is more a coachbuilt. The original rear end cargo area of the vehicle sides and roof are removed leaving the main chassis to the rear and the drivers cab. A new enclosure is created of side and roof, plus flooring, and frame. Internal fittings are added. The sides and roof will be composite panels, perhaps with reinforcement framing. Composite of various plastics, wood, insulation, metal sheeting.

For a converter creating a quality composite panel that has sufficient structural integrity must be a challenge.

 

[pappajohn]

Coachbuilt is built from the floor up on a naked van chassis and cab.
A pvc IS a regular van with furnishings built in.

 

[stevewagner]

Your build sounds like it will be very heavy.

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