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Hello again my fellow van dwellers.......I had some insight and wanted to share and get opinions about me insulating without some type of vapor barrier is defeating the purpose of insulating.I agree that using poly is only asking for trouble because of far as I know....has the capabilities of allowing the exterior of a home the ability to breath so to speak but at the same time stops drafts.....has anyone else thought of this or tried it.....opinions....I might be over looking something.....
house wraps are designed to stop liquid water, but allow water vapor to pass through, think Gortex.

For the inside-most layer you want to completely block the inside humidity.

This is difficult in a van.

I personally think use foam that is impervious to moisture, use a lot of forced ventilation in the living space and leave enough air circulation inside the gap so things can dry out when weather allows.

PNW type climate changes things, need to regularly super-heat the space I guess.

Especially be sure not to block the drip holes to the outside at the bottom of the body panels.

If you really want optimal sealed insulation, buy a reefer box truck.
I have to look into this a little more and get back to everyone on my findings........ it is....and I quote.....unique material that prevents the infiltration of air and water,but lets water vapor escape to prevent rot and mold inside walls.....I am going to go this route with my all I have to figure out is how to keep the roxul off the steel.....looking into the Styrofoam soffit vents you use to vent the attic space......I hope others look into house wrap scenario.....check out DuPont's web site and see for yourself..........might solve a lot of problems in the insulating a van department......I'll be the guinea
the problem as I see it is not a problem at all. what are you planning to use for insulation? basically in a vehicle you don't have problems with rot or mold unless you use materials that absorb and hold water then you don't air out your vehicle. you will never make the inside walls air tight and if you somehow could how would water get in? highdesertranger
The problem is that house wrap is designed to stop liquid water like raindrops from passing, but allow water vapor to pass.  Well, humidity IS water vapor, so it will pass right through your house wrap and condense on the van's metal walls, soaking your insulation.
What OP said x2
Yes, the only point of a **vapor** barrier is keeping the inside warm humidity from reaching the cold metal.

The only point of house wrap is protecting the building materials from outside liquid rain.

The former is quite difficult, but if you are going to try, need to choose material that stops water vapor. If you don't get a complete barrier, you may just be trapping condensation in the cavity.

Most people **want** to allow some air circulation in the insulation cavity to help reduce the length of time condensation remains sitting on the metal.

Yes this does reduce some insulation effectiveness but saves the body panels from rusting out from the inside.

Using the house wrap there may help adjust that balancing act a bit, but I suspect will just result in the moisture remaining there longer.

A decent heating system and good active ventilation takes care of the problem without trying to get a complete vapor barrier IMO.

Why don't you want the Roxul to touch the steel? They claim it repels moisture. . .
Majikman, a couple of basic questions about that since insulation will be part of my van build-out. :
1. What is house wrap made of?
2. Do you install it between insulation and bare van wall?
3. Is it meant to act similarly to the way Goretex clothing is supposed to work? That is, block out rain and wind but still allow some air in to cool the body inside and to prevent body moisture/sweat from collecting on the inside of the garment?

I probably should have read all the insulation forums and how-to posts on it first. I didn't. I'll do that next. Maybe here, as well, answers will inform beginners and the more experienced. Or not. Anyway thanks for the question.

For starters I thank those who responded with their input......sometimes we need a different as for Roxul,which I plan on using,over time it will absorb moisture.....I've seen it.....and the reason I am thinking of putting Styrofoam soffit vents first(against the metal) before the roxul......the channels will allow air space......but.....might lose to much interior space.....then I thought of using perforated soffit.....cost factor might be an issue....gonna look into that.....atm I am still 85% sure on using house wrap for vapor barrier......spoke with my friend who is an engineer and he agree's that it is a better alternative to poly....roof vent is a must we both agreed I am working on the I insulate with spray foam underneath...painstaking job I'm sure......or do I just go conventional with the pink foam and laminate......keep in touch my fellow van dwellers.....I'm on a mission
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