Insulating a Cargo Trailer

[Day Dreamer]

Hello All!! It's been a while since I've been here. Got hit hard by the covid shutdown killing my business, losing jobs due to layoff etc. and divorce (lost house). Now finally getting back on track.

I had been planning on "hitting the road" as a back up plan right before covid (which is now my forever back up plan which is good to have). Experienced camper and backpacker so easy adjustment. Way easier than thru hiking the AT. haha

So I bought this 5x8 cargo trailer. My plan is to make it mobile business and tiny camper combo until I retire (I'm 58 but probably like many here some life events kinda screwed me for "lush retirement"). Depending on how the stock market shakes out now I have 5-10 years of work left.

I have the trailer gutted and I am getting ready to insulate with -

Johns Manville R- 6, 1-in x 4-ft x 8-ft AP Foil Faced Polyisocyanurate Board Insulation​

My question is - Should I install foil out or in? I'm getting conflicting info. I will be using it mostly spring through fall.

Thank you!

 

[bullfrog !]

For me ( I am no expert ) it would depend on the temperatures I would be in, what type of heat/cooling I would be using and what type of ventilation. Is the foil meant to be a vapor barrier? Will there be a ventilated air space between the insulation and the trailer wall which I assume is metal? Condensation would be my main concern. In such a small trailer any heat source is going to be almost too much! If you are using a dry ventilated heat source you probably won’t even need insulation, in fact you may need more ventilation to prevent condensation from your body heat. In summer unless you have access to grid power for AC you will need lots of cross flow ventilation and external shade (parking in the shade really helps) like a shade structure or elevated roof rack with maybe a reflex or Mylar reflective surface will help. People have used a misting system as well but the outside surface of the trailer can be damaged by deposits left by the water deposits evaporating but in dry climates it can lower the inside temperatures at least 10 degrees.

 

[Day Dreamer]

For me ( I am no expert ) it would depend on the temperatures I would be in, what type of heat/cooling I would be using and what type of ventilation. Is the foil meant to be a vapor barrier? Will there be a ventilated air space between the insulation and the trailer wall which I assume is metal? Condensation would be my main concern. In such a small trailer any heat source is going to be almost too much! If you are using a dry ventilated heat source you probably won’t even need insulation, in fact you may need more ventilation to prevent condensation from your body heat. In summer unless you have access to grid power for AC you will need lots of cross flow ventilation and external shade (parking in the shade really helps) like a shade structure or elevated roof rack with maybe a reflex or Mylar reflective surface will help. People have used a misting system as well but the outside surface of the trailer can be damaged by deposits left by the water deposits evaporating but in dry climates it can lower the inside temperatures at least 10 degrees.

Thanks for the reply! It will be used mostly in the spring to fall so warm temps. I plan on starting out with A/C possibly an RV unit. No heat for now.

I don't plan on gluing it to the inside but there will only be a very small air gap if any between the trailer and insulation.

Right now I'm living in PA so it's not a very dry climate and my trips will be east coast. My travels will eventually include out west (BLM land) and Florida.

Ventilation won't be an issue as I will be installing a Fantastic fan, two small windows and a small side door.

Down the road (no pun LOL) I will be adding solar as well.

 

[bullfrog !]

The foil side is usually facing the side you want the heat to stay on. Having a ventilated air space between the metal surface of the trailer and the foil would be very effective in my opinion but take up a lot of space. Really to me the foil if you are putting it directly against the metal, is a waste. Most buildings with vinyl siding face the foil towards the interior as it makes heating the inside more effective and serves as a vapor barrier. With a roof top 13,000 btu AC in such a small space won’t need much in the way of insulation. Plain ridged foam installed so there are few thermal bridges ( transfer of heat thru metal ribs ) by using foam tape over then covered with thin plywood or paneling in my opinion will be plenty. Window shade material or temporary awnings will help during the day as well. Again I ain’t no expert! If solar is mounted on the roof use an elevated rack as the panels create a lot of heat underneath them in the first couple of inches and won’t work as well without air flow in that area. Also bright white exterior and white insulating roof coatings really work in extremely sunny areas. If you are not going to glue insulation make sure it fits tightly as it will deteriorate as it vibrates going down the road. Again this is only my opinion and I usually am in the dry Southwest which does get cold sometimes in the winter so maybe if you are going to cover the insulation with interior panels and are using foil backed insulation with a huge RV roof top Ac consider facing it in.

 

[maki2]

In a trailer some times you will be trying to keep heat in and other times you will be trying to keep it out. So that means it is pretty much irrelevant as to what direction you face it. Plus in order for reflective heat to work it can’t be up against other materials. So no matter which way you face that reflective surface it is going to do a whole lot of nothing. The foam is the insulator in these situations.

But if you are applying tape to it then choose to tape to the plain side as the micro thin aluminum can be peeled off and stick to the adhesive so that means the tape might come loose.

 

[LargeMarge]

If I was me, I might gap between the outer shell and my first inch-board of insulation.
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Another air-gap, then a second inch-board of your insulation.
And I might coat the inside of the shell with an adhesive-back acoustic insulation... this doubles as a sound barrier plus significantly reduces thermal transfer.
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With the adhesive-backed against the inside wall, I would anticipate significantly less condensation.
I base my opinion on our two decades full-time live-aboard in our home-made ExpeditionVehicle.
We used the adhesive-back acoustic insulation, a gap, 1" pink-board, another air-gap, then 2" foil-side poly.
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With this system, we rarely need to run the Wave 3 catalytic converter above 40°f.
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For windows, we built with 3010 (three feet wide by a foot tall) dual-pane sliders designed for a stand-still house.
We mounted these at our eye-level standing inside, about eight feet above pavement.
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Small windows, obsessively excessive insulation, and No! Holes! In! The! Roof!.
Our tiny home is quiet and temperate.
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For plenty of portraits plus our reasons for our decisions, please peruse our introduction:
https://vanlivingforum.com/threads/expeditionvehicle-build.44908/#post-576110

 

[tx2sturgis]

With foam that is 1" thick, and the vertical ribs on the trailer are probably 1" depth, this means your interior wall will almost surely be right up against the surface of the foam. In other words, a 'sandwich'.

So the foil will have minimal (to zero) thermal effect, but in this case, the foil should face the interior, more as a vapor barrier than anything else.

 

[Camper]

An air gap is an R-1... I'd fill it up with a Polyiso board which is an R-6 instead.

I used two inches of Polyiso in my cargo trailer which gives me an R-12.

 

[Spaceman Spiff]

According to Johns Manville installation instructions: shiny side out.
https://www.jm.com/content/dam/jm/g...P-Foil-Above-Grade-Exterior-Walls-9.10.13.pdf

 

[tx2sturgis]

An air gap is an R-1... I'd fill it up with a Polyiso board which is an R-6 instead.

I used two inches of Polyiso in my cargo trailer which gives me an R-12.

The OP is using polyiso.

 

[tx2sturgis]

According to Johns Manville installation instructions: shiny side out.
https://www.jm.com/content/dam/jm/g...P-Foil-Above-Grade-Exterior-Walls-9.10.13.pdf

Residential buildings and aluminum (or steel) skinned trailers are different.

The skin of the trailer already behaves as a vapor barrier, and in fact most polyiso already has a vapor barrier on both surfaces, so really it does not matter.

Again, a 1 inch thick sheet of polyiso that fills a 1" gap means the best use of the vapor barrier/foil (if there was only one on the foam panel) is facing inside, to keep interior moisture from penetrating into the foam and condensing on the interior skin of the trailer, especially during cold weather.

IF the air gap in the wall was say, 1.5 inches, or 3.5 inches, and the outer wall was brick, lap siding, stucco, or any other porus or semi-porus residential construction, then yes the vapor barrier should face that outside wall.

But this is probably an aluminum skin trailer.

 

[GoingMobile]

I have the solar panels on a roof rack on top of my van. The reason I mention this is that with about a 3-6" space in between the panels and the roof it acts as a shade keeping the van cooler even while in the sun.

 

[KD2USM]

If you have the money, I would look at closed cell foam installation. You will need to have all of your rough-ins done that you want in the walls. This can be very effective and has a high R value compared to thickness. It will function as both vapor barrier and insulation. If you had the room, I might look at open cell which does breathe, but to get the same R value as closed cell, you have to go about double to treble the thickness.

I just had my 30x40 shed sprayed a few weeks ago with 3-1/2" thick open cell foam as it is cheaper and the difference between no insulation and the foam is amazing. The biggest difference between closed cell and open cell other than R value per inch of thickness is open cell is not water proof and will eventually leak through if there is a leak in the wall it is covering. It does not damage the foam, but you would have to fix the leak and it might take a while to show evidence.

Prices local to me (central MO) are around $2 a square foot installed and they can do the ceiling, walls, and even the undercarriage. That's about $500 installed.

You will probably spend $350 for insulation board alone, plus glue and time to install.

Shade is your friend for certain when it comes to staying cool in a small box.

 

[Gr8ful]

Vapor barriers always go on the inside. White trailers reflect much better than black. Many foams, OSB & plywood give off a gas many can't tolerate such as formaldehyde. Spray foam may now be water based but wasn't years ago. I'd use it as seals well with no air leaks at all. It takes a new house about a year to "gas off" so consider getting it done now, leave a door open with a fan & it will be ready when you are. Good Luck!

 

[LargeMarge]

An air gap is an R-1... I'd fill it up with a Polyiso board which is an R-6...

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We have zero experience with your product.
Our intent with our patent-pending Multiple! Air-Gap! System!® is slowing the air exchange by limiting its inherent convection.
In a perfect universe, that intangible thermal bridge would be eliminated by eliminating the air.
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Fact is, some commercial fishing vessels use Vacuum Insulation Panels to form boxes to eliminate air exchange.
As the name implies, the air is sucked out of the panels to significantly reduce that thermal bridge.
http://e3tnw.org/ItemDetail.aspx?id=531#:~:text=VIPs have better insulating properties,-25 to R-30.
[relevant passage]
* "VIPs have better insulating properties than conventional materials. A one-inch thick vacuum insulated panel can provide an insulating value of...R-30..."
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I worked as an Air Courier.
We transported medical supplies in VIP containers for their thermal stability.
Some boxes are rated for as cold as -70°c continuous duty (seventy Celsius degrees *below* the freezing temperature of water).
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Of course, as usual, I ramble (semi-coherently, I hope...).
Moderators, feel free to punch my lights out.
I never take it personal.
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keyword:
Seattle Homeless Community Decry Towed RVs,
Seattle Bureaucrats Declare 'Victory!',
Seattle Junk-Yards Instantly Over-Whelmed,
Seattle RVs Recycled By chinese,
Seattle Winnebagos Inexplicably Appear In Pacific Ocean Garbage Patch,
Cranky Elderly Poster Recommended For Intervention

 

[Gr8ful]

https://www.action1insulation.com/materials/vacuum-insulated-panels/ is a secure site. The one listed above is not. $10-$12 per SF is a bit rich IMHO. I used 6^ SIP panels in the 12'x52' heated machine shop attached to the hanger with a R40 rating but R values are subjective as shown below for Reflectix.
The values utilized in Reflectix® R-value calculations for Interior “Air Films” are as follows: Reflective side of product: R-4.55 Down • R-1.32 Up • R-1.70 Horizontal. White side of Product: R-0.92 Down • R-0.61 Up • R-0.68 Horizontal.