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Self Build Guide - 8. Insulate, Cladding, Corners and Design Ideas

Article by Peter Smith - Caravans Plus

This is part of a series of articles on building or rebuilding a caravan. You can find the whole series here: Ever Wanted To Build or Rebuild a Caravan?


Before adding your cladding ensure you have completed the following:

  • All frame corners have been bolted or screwed together, at regular intervals
  • All 12V wiring for all lights has been added inside the frame
  • All 240V wiring for Air Conditioning, power points has been inspected by a qualified electrician
  • Any speaker wires, antenna cables, solar panel cables have been included
  • I suggest all fittings that may need a backing plate for screwing into, has been installed
  • Don't forget you'll need to mount an awnings later. The legs will aways be an exact number of feet from each other. The top mounts need to be level, while the base mounts can vary if necessary.
  • Plumbing and gas pipes would NOT normally be placed within wall cavities
  • Furniture should have already been added, and may sometimes be secured from the outside frame

    Caravan Frame and cladding
    Caravan before and after cladding

    In this guide I will get you from the naked caravan shell shown above, to the almost completed caravan.


    Insulation

    Wall insulation is best done with polystyrene sheeting, 18mm thick. This can be easily cut with a Stanley knife and if made a tight fit, will stay in place.

    Tip: Take lots of photos of walls so you know where wires and frame timbers are

    Caravan with wiring within frame
    Caravan with all wiring installed

    While the photo above was taken before all the wiring was installed, I'm sure you get the idea.

    It gets a bit fiddly around your wires. I did experiment with expanding foam into the cavity around concentrated wiring areas, and I'm sure if you persist it would work, but I , like the manufacturers was a little impatient and a little slack in this area. Maybe glad wrap, then a sheet of temporary ply screwed to the studs would assist.

    Any success in this area with photos would get a place in this guide, with acknowledgement.

    Caravan with insulation
    Caravan with insulation

    Roof insulation is better if you use the batt style. It mainly fits between the cross members but a little that covers the cross members helps soundproof the roof.


    Sheeting Walls

    Once you're happy that the insulation is complete it is really time to commit to the cladding. Are you sure you have done everything you need to do in that side wall?

    The wall sheet cladding (if using aluminium ) is around 250mm high (coverage after overlap) and up to usually 6m long. It is pressed into shape by a very few manufacturers within Australia and there are a few generic profiles and some that are owned by Caravan manufacturers.

    The most popular generic profile is called NF10, (that is what I use) and can be obtained from a few distributers around Australia, and most caravan repairs would also have access to it.

    NF10 side wall cladding profile
    Caravan aluminium cladding, NF10 profile details

  • Image (1) shows the face of the profile, the top edge is just plain and the measurements can be read off the tape measure
  • Image (2) shows the profile in more detail and how the next sheet slides up into the 'Pittsburgh' seam. The bottom sheet covers the staple or rivet that fixes the top sheet.
  • Image (3) shows the top sheet, before the next sheet is added. I also put sikaflex adhesive on each vertical wall frame timber.

    Caravans Plus have decided many years ago not to be a middle man in the supply of Aluminium cladding. The costs and risk during freight should be minimised so you will need to source this direct. To ensure this guide stays current, it is best to advise you to Google 'Aluminium cladding' or 'caravan repairer' to source this. At the time of writing CAMEC is able to supply this and many other specialist building materials. If you are unable to get NF10, other profiles may vary in coverage and depth of profile.

    Caravan with top sheet of aluminium
    Caravan with top sheet of aluminium
    This sheeting is easy to install with two people, but if installing alone, it is best to make two small supports that hold the sheet in place while you staple it with 4.5mm x 16mm long staples on all edges that will be covered by corner moulds, window frames or the sheet below.

    My method of placing side sheets is to temporarily position the sheet, go inside the caravan and mark the rear of the sheet where it is to be cut. For vents or windows that have sharp corners rather than curves it is advisable to drill the corner and cut to the drill hole. A curved drilled corner ( see image (1) below) is much less likely to be the start of a crack that can grow in stressed locations.

    Any wiring for external lights is pulled through holes during the addition of each sheet.

    The NF10 profile is around 8mm deep. This makes it relatively rigid, but requires an extra process where windows or corner mould is added. The high ridges in the profile should be reduced at the edges. Image (2) shows using a piece of timber and hammer to compress the profile for about 15mm from the edge.

    Installation of NF10 side wall sheets
    Installation of NF10 side wall sheets

    On this caravan I added 500mm of powder coated aluminium checker plate. This fits into the standard 'Pittsburgh seam' but must be glued to the frame to hold it in position. The true checker plate is only 2400mm long so needs to butt join the next sheet on a vertical wall frame timber. The bottom edge is made flush with the wall frame base and gets covered with an edge mould. A few countersunk screws close to lower edge wouldn't go astray.

    Wall sheeting almost complete.
    Wall sheeting with checker plate base

    You may have noticed the different colours, on the side sheets. This caravan was built when it was only possible to get white or grey sheets. I had them powder coated with some different colour-bond colours so that touchup paint was also available. The touchup paint was used to blend the 'White' CAMEC door with the rest of the caravan.

    Sheeting Roof

    The aluminium used on the roof is different from the side wall sheets. Due to the camber on the roof, completely flat sheeting is not recommended. The profile shown on the photos is called CP48. The profile gives extra stiffness on the front and rear walls, and very importantly allows for the sheets to curve over the roof camber.

    You will need to order the sheets and define the seams you need on each sheet. The seams are only added after they are ordered. Looking at the 'Lock Seams' shown on the image below you will see an 'UP seam' and a 'DOWN Seam'. You will need one of each to make a sealed seam. These always have silicone added on the roof after installation.

    Your roof sheets will bend or curve over to front or rear wall. This is called the transition sheet, because for a home builder you will treat the front and rear wall like the side wall and use 'Pittsburgh seams'.

    Method of joining Lock Seam.
    Lock Seams are compressed, then sealed with silicone

    Now it starts to get confusing. What sheet has what seam? The way I now do it, will work for any size caravan.

  • Starting with the centre sheet on the roof, it will have two 'DOWN seams'
  • All the rest of the roof sheets will have one 'UP seam' and one 'DOWN seam'
  • The two transition sheets will have an 'UP seam' for the final roof seam, and one 'Pittsburgh Seam' for the first seam down the front or rear wall
  • Additional front or rear sheets will have one 'Pittsburgh Seam'

    Diagram to show how sheets join
    Diagram of Roof, Front wall and Rear wall sheet joins
    Tip 1: As this sheet profile is symmetrical, I do get a 'Pittsburgh Seam' on both sides so that any off cut will still have a seam on it.
    Tip 2: When installing the lower sheet into the 'Pittsburgh Seam' on rear wall, always add silicone inside the seam. The rear wall is a real dust catcher, and I have repaired caravans where the dust has sucked into this seal then worked as a sponge to allow water to go into the rear wall.
    The procedure to join the roof sheets, and the roof to transition sheets is:
  • Make sure you have a firm surface and link the seams
  • Compress the end of each seam with a hammer to prevent the seam creeping apart
  • Starting at the middle of each seam, hammer the entire seam with a block of timber

    Roof sheets get joined on a firm surface
    Roof sheets get joined on the ground before being rolled up and placed on roof.

    If you have a large excess of width on your sheets, it may be safer to trim some off before installation, but the final trim is done during the installation.

    Roll the sheeting up, inside out, and get some help to lift onto the roof and unroll.

    Tip: The rolled roof sheeting is like a coiled watch spring, so take care here.

    After the sheeting is on the roof, line up the sides and position from front to rear to give the best location for front and rear 'Pittsburgh seam'. Staple the edges down then cut any openings for skylights etc. You would also staple around these openings to keep things snug.

    Tip: You are probably wary of climbing on that thin roof, so spread the load with a sheet of ply. But when complete you can crawl around and walk carefully.

    When fixing the front and rear wall sheeting you should use adhesive as well. You may need to add a few screws with caps, especially if you have a flat vertical rear wall. The bottom sheet, at the front and rear will need to either have a bend to attach under the floor, or finish at the corner with an edge trim. By now you are officially an expert.

    All cladding installed and trimmed
    All cladding in place, ready for the corner moulding, often called J-mould

    The sealing at the edges is done during the installation of the corner moulding.


    Corner Mould & Sealing

    Adding J-mould to caravan corners
    Adding J-mould to caravan corners. This J-mould is called 'Black TruLine'

    The corner moulding is often referred to as J-mould as this was the original shape. A 'J' on its side. It comes in a variety of styles, especially for vintage caravans.

    Predrill screw holes every 300mm along the centreline of the extrusion. These should be slightly oversize to allow silicone to squeeze out and seal around fixing screws.

    To install the moulding, start from the bottom at the front & the rear. I prefer to apply the silicone to extrusion, rather than on the edge of the caravan. For angular corners, remove a wedge on the short leg of the aluminium moulding and bend by hand. Progress upwards screwing as you go.

    When going around curves, ensure a screw immediately proceeds the curve.

    The corner mould I choose to use is called 'TruLine'. It is a softer than normal aluminium to allow for easier bending, without requiring annealing or heating in most situations. It will hand bend around curves of about 300mm radius, it can be curved around 150mm radius, with care, with the use of a mallet or block of wood. The following photos show the powder-coated aluminium. It is screwed and sealed before the decorative PVC insert is used to cover the screws.

    Truline is one brand of J-mould
    'Truline' is one brand of J-mould, that incorporates a decorative PVC screw cover.

    The 'Truline' brand, sometimes called 'American' comes in various colours and can have various coloured PVC inserts added after installation to cover the screws. The PVC is NOT part of the sealing process and may eventually need to be replaced due to discolouration and becoming brittle. You should get 10-15years out of it. At corners you may need to cut off the edges of the PVC to get it around the corner in one piece.

    Place silicone inside j-mould
    I place enough silicone to squash out both edges

    The J-Mould is pressed down and across to ensure a snug fit against the cladding. Ensure all surfaces that will have silicone MUST be cleaned with methylated spirits.

    Screw J-mould every 300mm
    'J-mould screws should avoid earlier bolts or screws used to attach roof..

    When screwed down, the silicone will squash out the edges - if it doesn't it may mean you will get a leak. At this stage, if there is some missing contact points, pad the silicone with your soaped finger to ensure complete contact. A spray bottle of household surface cleaner is ideal.

    Next spray the entire exposed silicone, and edges of the cladding and J-mould. Running your finger along the silicone now will take off any excess, without smearing it onto the cladding or J-mould because it has soap already sprayed onto it.

    Remove excess silicone
    Finish removing excess silicon on the edges with turps.

    A generous amount of silicon should remain on the roof join, but it should be 'SMOOTH' as any future leak will take dirt under the silicone and the dirt can be seen after the silicone surface is cleaned.


    Exterior Design Ideas

    The exterior shape, colour, and material selections can be very important to the way your van finally looks. I would recommend that home built vans go for the "Tough and Rugged" look that many modern Off Road vans have.

    It is very hard to achieve the perfectly smooth and flowing curved edges designs that some factory vans with plastic mouldings have. It is much simpler to allow yourself to have corners and chamfers rather than multiple curves.

    Below are some inspiration images of designs you can probably achieve. Notice the shapes are simple but they are made to look tough by addition of things like checker plate and dark colours around edges. If you can't hide something, make it stand out.


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  • 2 Comments

    • comment-avatar

      Brian

      I've personally been thinking of a rebuild for some time but never been sure what to expect 'under the covers'. This article, and the others is just great, and you deserve much credit and applause for them. But, I have one question. I am also very interested in the stability and aerodynamics of caravans and the heavier and higher design as is the current trend seems to fly in the face of common sense. I like my vans low with the centre of gravity down as far as you can get and still keep reasonable highway type road ground clearance. I also like to keep the weight just forward of and between the wheels to stop the dreaded sways. Putting the bathrooms out the back, almost as an afterthought also seems to go against good stability design. What are your thoughts on this essential design element? ?

    • comment-avatar

      Peter - CaravansPlus - CaravansPlus

      Hi Brian I am still working on these articles and hope to eventually cover most questions, but more than happy to cover your questions................. The tendency to go higher is purely influenced by more people wanting to go off the beaten track more. In many cases this is just to get off the road a bit more when free camping. A substantial part of the weight of any caravan is in the chassis , water tanks, gas bottles. The next greatest weight is what you add, in your lockers, boot, and cupboards. Heavy items should always be set on the floor. I really don't think the extra 100 or 150mm makes a significant stability problem................ Having said that I have seen many huge 5th wheelers that look like they could blow over with a side wind............ The only heavy item up high is the air conditioner, and it is always in the centre............... If you are a caravan park only visitor, or stick to formed roads (sealed or unsealed) you can still stay low. But even some driveways cause a problem with low profile chassis................... I think your idea that the bathroom is heavier than other parts of caravan is not correct (unless maybe you have a 16kg washing machine.) They are usually very open, storing usually lightweight items. Much better to have a bathroom at the rear than a kitchen with food and plates bumping up and down as you go over bumps................... I agree about weight being central and low, and 10 to 15% at the towball. My caravan that features in many photos is so stable even without WDHitch. I tried it at 130km in NT and it was stable on a good road, but I needed a fuel tanker after that test.................. Hope this covers your questions.

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