Insulating my self build campervan without a vapour barrier

So, here it is, the video I've been putting off! I wanted to go through the choices I am making for my van and the insulation products I'm using but very controversially, I'm not installing a vapour barrier which I know will lead to loads of comments telling me I'm a fool but I have weighed up the pro's and con's and for my van and the way we will be using it decided it was not needed for us.
for some good videos on vapour barriers to possibly help you make your mind up here are couple of links:

A good video for vapour diffusion:

A good source for why not to install a vapour barrier:

A couple making very good sense of it all:

Let me know your thoughts in the comments down below, but if your opinion is the opposite of mine, that's fine but be nice....

[disturbedjunglist]

I think it was vanology that explained the vapour barrier theory on a video I watched to day and it makes so much sense.

[Gotzy]

A very compelling argument and perfect timing for me to stumble across it, cheers dude

[andrewszabo]

This was very informative and helpful 👏 It provides a reasoned explanation for your decision and I would say that I agree with your evaluation!

[gordon]

Winter & Condensation. I was building my van in winter with a frost outside. Within 20 minutes of being inside, my van was like a rainforest, the condensation was just so very high. Time will tell whether you are correct, but after seeing my windscreen on the first winters morning of an overnight stay it really hit home the levels of condensation these vans suffer. I didn’t use a vapour barrier as such, I used high density foam wherever possible, diall insulation only in the difficult areas and sealed every hole I could find with aluminium tape. It doesn’t need to be air tight in my opinion, but you must stop the internal temperature meeting the external surface temperature.

[paulwitham]

Very valid points raised you have clearly thought long and hard on the subject nice to see you're not one of the sheep, haven't started my insulation yet you've given me a lot of food for thought 😰 hope everything goes well, crack on👍

[jameswalker]

Beautifully put. Totally agree. I used closed spray foam directly on to the panels (2 years ago) and so far no problems. No vapour barrier fitted. I’ve designed most of my wall panels to have plenty of ventilation, especially at the bottom, and they are all easily removed. Keep the van warm and ventilated when in use, and a dehumidifier in winter if possible

[PJDX]

Well argued case for omitting a vapour barrier. A good layer of closed-cell foam against the van metal should prevent a good portion of condensation which together with ventilation of the other insulation plus good drainage will provide a very workable solution. These features are easier to achieve for the majority of builders than a vapour barrier which, as you point out, really does have to be near perfect to get the desired effect.

[paulshanesmith]

2 years ago we converted a brand new Iveco Daily L4H3 which we now live in. That wasn't the plan originally but after two 90 day trips to Europe we hated being in a house. We stop warm air from touching cold metal by sticking foil bubble wrap to every inch of metal on the inside. We then insulated it with wool. 2 years on, a season sking in the alps and 2 summers in 30 degrees plus and we would recommend that method to anyone. We have no damp and the only condensation we get is on the windows of the cab.

[SelfBuiltStories]

We came to the same decision to not put in a vapour barrier. We were on the fence for a while but the more we thought and researched about it, and worked in the van, the more we swayed against it. Like you still open minded and will keep some areas accessible to allow us to check every now and then how everything's looking, and chose hydrophobic insulation materials. We're going with the approach of dry heat and air flow to combat moisture and the assumption that warm air will inevitably come into contact with cold surfaces and condense. We've experienced water collect in one of the pillars through a small leak in the roof, and then seeing all the holes throughout, even the ends of the wire conduit and things like that. Tricky decision to make though as there are so many variables and you need time to tell if you have a problem or not. So we'll see! 🙂 Good luck with the rest of the build!

[matts_shed]

Great video. At last! Some thought out logic! Well said sir.

[ClaroVAN]

Thanks for a very good explanation regarding vapor barrier or not. We have come to the same conclusion as you, ventilate properly instead.

[digb]

I had some deadlocks fitted to my VW Crafter a few months ago. I mentioned I intended to do a camper conversion. One thing the fitter said was don't use expanding or non-expanding foam insulation. He said they often find pools of condensed water in areas where the foam hasn't filled. Makes sense to me. I would though use a mildly expanding foam in areas like inside the roof bars and other areas difficult to reach. I would make sure the foam has completely filled the cavity though. This is purely for the small ribs that strengthen the bodywork. I would recommend using a proper gun and choosing your foam carefully. There are different expansion rates etc. I would use the closed foam adhesive on the panels themselves over the sound deadening material like this video shows. As for a complete vapor barrier over the whole lot I personally think it would be beneficial.

[alanhat]

Another thing to consider is the airflow from the cab heater, where the air gets in is obvious, the grille below the windscreen, but where does it get back out? On some vehicles there's an obvious vent at the back but that's by no means universal, my guess is that the manufacturer intends there to be an airflow through the walls & out the weep vents in the sills & various holes they've left around the underside.

[MarkloopRAF]

You are right. I've just bought an ex-Ambulance Service Command and Control vehicle to convert. All insulated etc, but no vapour barrier installed. It's 19 years old and the only bit of rust or rot was from a small leak in the back garage compartment where the extending NightScan lighting system was installed.

[richylad]

In one of the van conversion videos I watched, they were extremely thorough with vapour barrier and planning everything to minute details, yet still had external water leaks and other problems, so an external water leak is behind the barrier, then possibly trapped, I have gone for a hybrid approach, so I have access still. And like others have said if you ventilate the van and heat sensibly you should move moisture through

[whitevanman]

I'm starting my third build and have never fitted a VB as in my mind airflow will keep the inner walls dry and fresh and remove mosture in the same way as the air bricks in older houses. Never had a damp problem in the previous two.
Will now check your earlier videos as it's my first Relay.

[philipeastham]

Good reasoning here in my mind. I think that good ventilation is the key and not a vapour barrier. I compare it to loft insulation that we had installed at home a few years ago where the installers covered the soffit vents and the roof sweated badly with water vapour soaking into the roof trusses. There was nowhere for the vapour to go. Luckily we found out in time, uncovered the vents and installed more to be sure and no issues since so I don’t think I will be installing a vapour barrier but will be making sure there is adequate ventilation just as there is in a caravan.

[peterread]

Agree 100% with every word, I am sure you are doing the right thing. Over the past year I must have viewed just about every van conversion video several times, and at last someone has put out a video addressing all the concerns that I have had. Brilliant. Thank you so much. By the way, if you examine the "professional" conversions or talk to any conversion company, I don't think you will find any vapour barriers being used. As in any inside space, good ventilation is the key. Now, where I have I heard that?

[peterc]

Oooh controversial! It's your van, do it your way and stuff everyone else. Lovely job :-)

[baercontact]

Wonderful job, well done! Looking forward to it being finished. Will show it to my son, he has a Ducato.