Vapor Barrier

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vanman2300 said:
Another good question, I think, is has anyone ever opened up the wall of their van after a few years and what did they find for damage due to moisture?

It is a great question, one I've asked but have not yet seen answered directly.

Predominant climate type seems to be a big variable here, IE: are you insulating to keep heat in/cold out or the inverse, cool in/heat out. My gut tells me that's gonna make a difference with moisture in a steel vehicle.

Good discussion.
 
In most stock passenger vans, the floor, walls, and ceiling are all vented to prevent moisture buildup. The floors use a heavy fiberous wicking material to draw the moisture away from the metal so that it can be evaporated through the carpet. Even though not obvious, the side walls are vented top, bottom, and around all of the windows. The headliners are usually perforated, or made of breathable fabric, as well as being vented around the perimeter.

The holes in the ribs are designed to help this ventilation scheme, as well as to prevent moisture build up inside the ribs from condensation, because if they weren't present moisture would build up inside the sealed ribs.

I may or may not be using the term condensation correctly here. What I am referring to is when metal sweats do to the difference in temperature, humidity, and possibly even barometric pressure between the two sides of the material. The result of which is moisture occurring on the inside of a seemingly sealed object such as the skin of a van. This same process occurs in homes with metal framed windows. Under the right conditions we can be talking about a sizable amount of water in a single day, and due to the size of a van we can be talking cup fulls.

If the skin of the van isn't vented in some way via either direct venting, or some type of wicking material to transfer the moisture to the interior, it will become trapped between the vehicle skin and the interior walls/insulation leading to rust, mold, mildew, and dry rot if it can't be dissipated.

This is the exact reason that many camper and conversion vans, and many RV's & TT's in general, are riddled with mold and dry rot problems. Fiberglass will sweat just like the metal will. To my knowledge there is no way to stop this process, besides building in such a way as to compensate for it.

This is just one of many reasons that I have come to the conclusion that a stock window van with factory finished floor, walls, and ceiling is the best base to start a camper van with. All of the hard work is already done, no extra insulation is needed. It is easy enough to add curtains to prevent heat loss/gain through the windows if you choose to do so, and the opening windows will provide you with the necessary ventilation.

I agree that if you're starting with a stripped van you're probably going to want to add interior floor/walls/ceiling, but if you don't do it correctly, with proper ventilation to the inside skin of the vehicle, you WILL have mold, mildew, rust, and dry rot problems in the future.

Someone asked if anyone has torn out the interior of a conversion or camper van. I have rebuilt many over the years. RV's & TT's too. They are typically full of black mold and dry rot, many are sopping wet behind the interior paneling, and it was not caused by leaks, it was caused by condensation.

If you're building your own rig, history is the best teacher. Don't repeat the failures that others have made before you. Don't create an environment to trap moisture and grow mold and rust.

There's nothing more important than your health and well being. We are living in these rigs, not just occasionally taking them on camping trips. If you get mold, you're breathing that every day and every night. It's just not worth the risk. You can't smell carbon monoxide, but it can kill you. You might not be able to smell the mold either, and it's effects might be slower, but why take that risk.
 
Something I have not seen addressed is the idea of painting the inside of the steel body with a water-proof (plastic) paint, to keep the moisture OFF the steel. Let it trickle down to weep holes at the bottom, and out of the vehicle.
Condensation being a given, I am thinking controlling and directing it to a safe place is better than trying to prevent it with too much insulation.
 
I only insulated the ceiling and the wall sections in the rear where the foam mattress is crammed up against the wall.  I have seen mildew on the outside of where a mattress has been up against the walls.  I have not seen cold enough weather yet to know if I will have condensation or not.

I can tell you that after 90° days at night when cooler I can feel the cool metal skin that is not insulated and it must be helping interior cool down.  The polysio feels neutral so is it holding the heat in or just not helping to cool.  I don't think the roof insulation that also feels neutral is holding heat that would not go straight up out of the vent anyway and contributing one way or another.  It is also cool when the sun is blasting the roof in mid day so not radiating heat.  Also with my fans I am at ambient or very close to ambient but instead of sitting in the sun waiting for a full solar charge I would rather be in almost any water trying to cool off.

I will report back this winter about the condensation.
A SEEKER

 
 

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LeeRevell said:
Something I have not seen addressed is the idea of painting the inside of the steel body with a water-proof (plastic) paint, to keep the moisture OFF the steel. Let it trickle down to weep holes at the bottom, and out of the vehicle.
Condensation being a given, I am thinking controlling and directing it to a safe place is better than trying to prevent it with too much insulation.

Rust is really your last concern. Its the most final concern too, rust can kill a rig. Water equals life. Once you have water something is going to try to eat all the organic material in your vehicle. I found a mushroom growing out of my carpet in the storage space under the bed. That wasn't from condensation, it was from a leak. After I pulled all the osb up, the paint looked factory fresh. I imagine if I had a lot of drain holes in the bed of the van the osb would have been able to dry out.
 
LeeRevell said:
Something I have not seen addressed is the idea of painting the inside of the steel body with a water-proof (plastic) paint, to keep the moisture OFF the steel.  Let it trickle down to weep holes at the bottom, and out of the vehicle.
Condensation being a given, I am thinking controlling and directing it to a safe place is better than trying to prevent it with too much insulation.

The existing paint on the inside walls should already be waterproof.  Otherwise I would think you would have pretty immediate rust problems.


Weep holes are good at preventing standing water buildup, but I'm not sure if they would adequately prevent moisture build up.

I would create an air gap around the inside of the skin, then vent it all the way around through to the interior.  If the interior walls are "floating" it should create enough air movement to the skin to keep everything dry.
 
A Seeker,

I keep a small inflatable boat in my rig that can double as a soaking tub too.
 
907KHAM687 said:
Rust is really your last concern.  Its the most final concern too, rust can kill a rig.  Water equals life. Once you have water something is going to try to eat all the organic material in your vehicle.  I found a mushroom growing out of my carpet in the storage space under the bed.  That wasn't from condensation, it was from a leak.  After I pulled all the osb up, the paint looked factory fresh.  I imagine if I had a lot of drain holes in the bed of the van the osb would have been able to dry out.

Be really careful about holes in the floor, as they can let exhaust in.

Do you know where the leak is? 

Maybe some sort of storage area ventilation could help get everything dried out too.
 
Off Grid 24/7 said:
Be really careful about holes in the floor, as they can let exhaust in.

Do you know where the leak is? 

Maybe some sort of storage area ventilation could help get everything dried out too.

Yeah, I wouldn't drill holes in the floor. That was back in the 90's, water was leaking in around the brake light and it soaked the osb floor of the carpeted conversion van. Not a big leak, just a little bit every rainy Seattle day. Osb is like candy to the fungus among us. If I had know it was happening it would have been an easy fix, the van was jet black, the sun boiled water in that thing. I gutted it, put a new transmission in, and it popped a freeze plug and I wasn't watching my gauges. Wisp of steam and a cracked block. I walked away from that van, I still feel like I let her down.
 
That's one of the best answers I've seen...... thank you Off Grid.

Seeker that tub you're soaking in must be freezing cold! I'm from the north and that would be a little rough for me.
 
I asked a friend of mine who is a mechanic for a school board and cleans / cares for vans often. He says that condensation will happen between the metal wall and insulation but it doesnt matter because throughout the bottom of the van there are small drain holes so the condensation cannot accumulate and become water and eventually mold. He said a hobo broke into one of the vans and slept and urinated in it. He pressure washed the inside and the water dripped out thru the drain holes. I think what I'm going to do is to continue building the van the way I am. Then in a few months I'll take the van insulation apart enough to see if condensation/water/moisture/mold is an issue in the walls. I guess one advantage of having 2 inch rigid foam insulation is that it wont bend, meaning that there are lots of gaps between the insulation and the van's metal wall. Hopefully enough to allow things to dry out in the wall. If condensation is a big problem, I'll buy one of those fancy/expensive Dickenson heaters that are fully vented and add nothing to the interior but heat. That should dry things out well and solve any moisture issues. They are over $800 for those heaters so thats plan b at this point.
 
vanman2300 said:
That's one of the best answers I've seen...... thank you Off Grid.

Seeker that tub you're soaking in must be freezing cold! I'm from the north and that would be a little rough for me.

Tub?  That would be the horse water trough thingy.  What can I say, it was HOT!  I normally stay on the coast where I have the ocean or waterway available.  It was empty when I found it besides a few leaves that had fallen in.  The water temperature was somewhere near what Florida springs are year round I would guess.

I have lived in Florida since 89 but I grew up swimming creeks and rivers in the Appalachian mountains and I am sure they are usually colder (the creeks anyway)
A SEEKER
 
Springs in my Florida AO are cold. Wakulla and Horn Springs are near freezing year round. The water off the Gulf Coast tends to be warmish, even in winter.
 
LeeRevell said:
Springs in my Florida AO are cold.  Wakulla and Horn Springs are near freezing year round.  The water off the Gulf Coast tends to be warmish, even in winter.
Lee, my favorite Silver Glen Springs is around 72° all year.
 
I read somewhere on here that somebody used the plastic they use to protect new carpet installs that has a mild adhesive on one side. I was thinking of using that after my insulation and before my finished walls inside.
 
I remember reading moisture goes from warm to cold.
So in a van, moisture travels through the wall and hits the cold steel shell and condenses. So I think the vapor barrier should be as close to the passenger compartment as practical.
 
Bdog1 said:
I remember reading moisture goes from warm to cold.  
So in a van, moisture travels through the wall and hits the cold steel shell and condenses. So I think the vapor barrier should be as close to the passenger compartment as practical.

Moisture does not go through steel. What happens is that water vapor in warm air condenses on any surface that is significantly cooler. That is, moisture goes from warm AIR to cold walls and windows. Technically, you will get condensation whenever the walls and/or windows are below the dew point of the air, but that's not useful to know since most of us don't usually measure the dew point of the air in our mobile houses. But what it boils down to is that the higher the humidity of the air, the less of a temperature difference between the air and the surface it takes to make it sweat.

Most of the moisture in a house, van, RV, or tent comes from people breathing in it. As a number of people have already said, the key is to always have some ventilation, which brings the humidity down and reduces condensation.
 

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