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I don't have a van yet. But, I suspect a cargo van is in my future. I would like to insulate it myself. But, frankly, I'm afraid of creating favorable conditions for mold between the van's metal skin and insulation.

I expect to be sleeping inside the van at times when it's cold outside, creating a dew-point situation inside the van. Also, I spend time in the PNW where moisture is in the air.

This is what I think I know about preventing mold: block moisture with vapor barriers over the insulation, provide drainage for any moisture that collects, and create air flow. Also, I wouldn't use fibrous insulation which holds moisture, rather something like Polyisocyanurate sheets and/or Reflectix

If I install good insulation and tape up a full vapor barrier, will that be able to totally stop moisture from getting between the metal and the insulation? Is a complete vapor barrier even possible along all of the jagged edges, holes, and compound curves of a van's interior?

I'm thinking that even with good air circulation inside of the van, air flow will not reach the space between the insulation next to the van's metal skin. Furthermore, I don't think I've ever read of anyone creating drainage holes.

Suanne ... in research mode

In my continued research, I found a reply from expert Laren Corie over on the VanDwellers Yahoo Group. It's starting to answer some of my questions. Here are some excerpts from that reply:

Laren Corie 9/15/13 Wrote:... foil will not work, except where it is adjacent to an air space. The areas where something is touch it, do not have any Rvalue. However, it is also highly advantageous to have a drainage plain, so that when condensation forms on the cold foil, that the moisture can run down it and out the fender drain holes, rather than soaking into the insulation. But, ideally spray closed cell foam, directly onto the inside of the fender panels will keep moist air from ever getting to the cold surface, thereby radically reducing the chance of condensation. ...

Never have two vapor barriers (the plastic and the metal of the body) with a gap between. What that will do, is to trap moisture between (there is no such thing as a vapor barrier that does not leak. So, when you have a vapor barrier on one side (the metal of the body) the other side needs to be able to breathe moisture. In this case it needs to be able to dry to the interior. A vapor barrier would stop that from happening and your foam rubber (very expensive insulation) would become a wonderful medium for mold spores to grow on/in.

So, you should make you walls air tight, but not totally impermeable to moisture diffusion, If you drive your van regularly, then drying is not difficult. Vehicles are very leaky while moving, and the dash heater takes the dry Winter air, and heats it further to make it even drier. Just blast the heater when you drive (this is all during the heating season) and everything, including the walls should dry out, if you allow that to happen, by not putting in a vapor barrier. We used to think vapor barriers were a good idea for houses too. But, time and building science has shown us the folly in our earlier thoughts ...

-Laren Corie-
Natural Solar Building Design and
Solar Heating/Natural Cooling/Energy
Efficiency Consultation Since 1975 ...

Laren's full response here:
Thanks for that Laren's post Suanne. That make perfect sense to me. Putting in a real air-tight vapor barrier would just trap the moist air inside next to the van making matters worse. Laren is the one who got me onto PolyIso and is what he recommends so that is probably your best bet.