Condensation Question

[foamer01]

I was chatting with a RV manufacture about his traditional built camper (which I liked alot) and I mentioned the possibility of getting a Aluminum Cargo trailer. He shrugged his shoulders and said watch out for the condensation that I would most likely experience. So the question is this; Do you notice a condensation issue in your converted CT? Thanks!

[KennethW]

He is going to poo-poo any the that stands in the way of a sale. A cargo trailer will have to be insulate to prevent condensation and-or vented when you are in it. Your breath has a lot of water in it. Same with all small hard side campers !!

[OverTheTopCargoTrailer]

Condensation inside a metal trailer , no way !!
Besides 100% alum = 100% no rust

[jjvw]

Just make sure you use battens to install an insulation layer over the metal studs. My all aluminum trailer has 2" foam plus 3/4" foam thermal break and FRP in the ceiling and 1" + 1/2" in the walls. Deer camp was unusually cold last year with 0-10º lows. Heated to 60º with a Buddy heater only for an hour before bedtime, it fell to 40 by morning. The walls and ceiling never really warmed enough and you could see where the ceiling beams were because of the light condensation over the aluminum beams. You definitely need a good thermal break.

[len19070]

My response to any questions about Condensation is this. It all comes from you Breathing.

In any trailer I have ever owned I have burned a candle.....SAFELY and have never had any problems.

Happy Trails

Len

[OverTheTopCargoTrailer]

My response to any questions about Condensation is this. It all comes from you Breathing.

Happy Trails

Len

I'm not a real bright fellow, but please explain to me, if you fill a glass with cold water & ice cubes, set it on a tabel inside a 90 deg hot room.......
how hard do you need to breath on it to get condensation ????

[WoodSmith]

OTTCT, I actually laughed out loud.

There is nothing like a simple example to clear things up.

That said, humans are definitely wet creatures & we do exhale quite a bit of moisture.

[Prem]

Cold metal contacting warm air always produces condensation.

You can't eliminate either, but you can put something in between them that is AIR TIGHT. There's only one thing: Spray foam.

I spray foamed my bus motorhome years ago. I wish I would have spray foamed my cargo trailer instead of using block foam.

The interior plywood warped from the inside of the wall.

[lrrowe]

Prem,
First of all, I think I do understand the overall benefit of spray insulation over panels. But what would you do to metal uprights? How would you spray over them? And why would having the spray insulation at say 3/4 inch over the metal studs be better then putting a second layer of blue insulation horizontally over the first layer with taped joints to address the thermal bridging?

I am not trying to attach your input, but just trying to understand the physics. If possible, I would like spray insulation, but I believe for my use, it would not be affordable for me.

Thanks,

[OverTheTopCargoTrailer]

Grasshopper

Prof Prem is always right
#1 Never question Prof Prem
The sprayed foam blocks 100% of the air - NO AIR - NO CONDENSATION

If you sprayed foamed a glass, it will not sweat when filled with cold water & ice.
I have a thermos bottle with a vaccume between layers - it also does not sweat
It even keeps ice for almost 3 days.
Creating a vaccume in your trailer is most difficult.

Cheers OTTCT

[lrrowe]

As I tried to say, I was not questioning Prem at all. I am just trying to understand things better.

[MtnDon]

Keeping the air and the moisture it may contain away from the inside face of the metal skin is very important. I sealed each piece of foam inset between the ribs with foam in a can around the perimeter of each foam panel. In a few years we'll see if that worked as well as I hope it does.

An inside layer of sheet foam over the ribs does a good job of breaking the thermal bridge, but likely has to be at least an inch thick. Ours varies from one inch to three inches depending on where on the roof and walls.

When you come right down to it, OTTCT may have had the best idea with the wood framed, plywood on the outside and then the metal skin method CarMate employed. Not everybody has a CarMate dealer close by, nor can everyone take time to drive across country to get one. Every other manufacturer with a dealer presence in my area, stated they could not do plywood on the outside wall.

[lrrowe]

Thanks MtnDon,

Another thought I had has to do with the ceiling metal cross members. If they too can create a condensation area, what about running a wooden cross member across the top connected to the cross member on the side and then providing a non- metal surface for the ceiling and thus help prevent the thermal bridging of "cold" to the ceiling through the metal cross members (ugh, what a bad long sentence that is). This is because no metal contacts the ceiling panel. If you did this, added height helps when ordering the CT.

I remember seeing one posted picture in this forum with wooden cross members added. Maybe it was Jerry in a OTTCT post.

[OverTheTopCargoTrailer]

Bob

Now I know your dreaming about OTTCT 2.0 ... I did the wood cross members with R19 Denium insulation.
The denium needs to be compressed real tight, remember the freezing skin at 37 deg
Then i put runners from front to back & another 3/4 or 1" foam layer under the denium.

Get the CarMate ...... Just save another 2 years to finish. I'm only about 40 into it , including goofs.
I just dropped the last 8 on the mega battery, mini split & outback inverter,
But when the world ends I'll have power for a few extra days.

OTTCT

[MtnDon]

Roof / ceiling.

I first infilled the bays between the cross ribs with 1" foam rigid sheet foam.

Then I ran two wood strips (battens?) down the length, perpendicular to the roof cross ribs in from the side walls about 18" on one side and 24" on the other. The difference was to accommodate ease of installing our shower. Probably made no real difference. Our roof has a slight arch to it, BTW; not really flat though Lark calls it flat. Those longitudinal strips were cut from poplar as I wanted something harder than pine or whatever. They were fastened with self drilling flathead metal screws. The hardwood was predrilled and pre-countersunk. I cut them to 1/2" thick x 2 5/8 wide. The area between the wood battens and the exterior walls and between the pair of battens had 1/2" foam glued to the insulation above it. I used a polyurethane moisture activated glue and used plenty of 1x2 supports and strips of 1x4's to prop the foam securely in place. At that point the entire roof was brought to the same plane.

After the glue had set (overnight) I cut more sheets of foam to fit wall to wall. Two inch thick in some places, 1" in others. These foam panels were also glued with the polyurethane glue. I used poly washers made special to secure sheet foam insulation in addition. The screws through the washers anchored into the poplar hardwood strips. I also used some more temporary braces to hold the foam sheets up at the wall edges. The center conformed to the slight curvature of the roof as the washered screws were tightened to the poplar hardwood strips.

Hope that is clear to understand.

All that messing around gave us thermal breaks from the ribs and no visible interior screws anchored to the steel ribs.

After the ceiling insulation was completed I did the walls in a similar manner using 1" or 2" foam over the ribs and interior structural wall plywood. The bed area received the extra thickness.