I have had many conversations on various forums and with materials suppliers about the best way to insulate. In the main we are looking to insulate against cold because if it is hot we can simply open doors and windows. There is a plethora of available materials and methods but there is no definite right way to do it.
With the van being a big tin box as well as insulation you have to consider condensation. As well as the general atmospheric humidity moisture is introduce by us breathing and perspiring, by boiling and cooking and by the bathroom and washing. If you cook with gas, which we don’t, you will introduce a lot more condense from the combustion but I assume no one would consider actually heating such a small space with naked gas flame.
The warmer air is the better able it is to carry moisture. However when warm moist air meeting a cold surface the moisture will condensate. It will do this against the outer skin of your van and even the insulation and structure between the inner and outer skins if it is colder. Uncontrolled this condensate could build up, saturate your insulation, the ply lining and wall boards and even rot the outer skin of the van from the inside out.
Don’t let anyone pretend you can prevent this by installing a vapour barrier behind the ply lining thus creating a void full on installation. That changes nothing and may even make it worse. You cannot create a sealed void so air from inside will get in there. No, the best solution is, as in your home, to keep air moving. Condensation may still happen but it will evaporate again and move away as the air circulates. Indeed a perfect solution would be heat recovery ventilation but this is a small space and that is hardly practical.
As for insulation materials themselves the first rules are not to use anything hygroscopic (absorbs moisture) as it could end up as a soggy mess and avoid mineral wools that will discharge fibres. How to install the insulation is important too remembering that you have to get into all of the structural ribs and that years of driving on bumpy roads high shake your insulation to the bottom.
One extremely good solution would be spray foam which is a job best done professionally. Care needs to be taken to only spray as much as can expand into the space especially within box sections. Get this wrong and as the foam expands it will buckle the bodywork. However one big concern I have about it is the implication for body repairs should you have the misfortune to have an accident. Panels will no longer be easy to straight or replace and will add significantly to the cost of damage repair. As a result your insurance company will likely argue with you about the cost.
In the end we are going to use several methods.
- Primarily we will stick self adhesive DoDo Mat, a dense sponge foam mat designed as sound deadening as well as thermal insulation, to all the flat panels we (well actually Sue’s small hands) can get at. WE are going to start with a layer of 6mm between structural members and into ridges such as the roof ribs. On top of this we will add one or more layers of 6mm and 12mm. In the larger voids below the waist line we will also stuff polyester insulation wadding.
- The structural members will also be filled with polyester wool. This will be fed / pulled in using fibreglass rods to get at the very difficult and may even need a couple of new holes to get at some sections.
- The ply floor will be lifted and strips of 6mm insulation laid between the ribs and then 8mm high density floor foam laid before fixing the ply floor back down.
- All the doors and the cab area will be insulated with self adhesive DoDo mat.
Our accommodation windows are twin skin and they and the roof vents have thermal blinds. And finally we will use SilverScreen covers on the cab windows at night.