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Old 04-12-2010, 09:02 AM   #1
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Creating a Thermal Break between Outside Skin and Inside

For years I've thought that a thermal break between the outside skin/ribs of our Airstreams and the inside skin would greatly reduce the flow of heat between the inside and outside of Airstreams. The biggest disadvantage of aluminum frames as a skin material is its high thermal conductance. It readily conducts heat. Aluminum window frame manufacturers have found a simple thermal break greatly reduces the thermal conductance of the window frame. A good thermal break can stop 40% or more of the heat flow between inside and outside of aluminum window frames. Here's an example:


Since doing the renovations on my trailer, I've regretted not installing a thermal break at the time, but I didn't know what to use and where to get a suitable material. Now that the renovations are long over, I've found just the material. It is a tough EVA foam 1/16" thick which could be very easily applied to the inside face of the ribs just before the interior aluminum skin is re-installed. The EVA foam could be applied with a very thin, very tenacious and durable adhesive tape used in making sails. This thermal break should greatly reduce the heating and cooling load on the trailer as well as greatly reducing the tendancy for the interior skin to sweat. Strips of the foam could be made a bit wider than the rib face with the adhesive tape pre-applied. To install would mean cleaning the rib faces to create a clean mounting surface, peel the paper backing off the foam and press onto the rib. Then you would screw or rivet the interior skin to the ribs just as normal.

Anyone game to try it on their project! I'll make you a really great deal on ready to use EVA strips, say $2 per 6' length of EVA foam with the adhesive applied and ready to use. I would cut strips to be about 1/4" wider than rib face. Let me know. I could send samples. Bob T.
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Old 04-13-2010, 08:22 AM   #2
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Bob, a good idea. My 1956 Flying Cloud is not far along enough to take you up on your offer, but I will look forward to whatever progress others make. Eventually, I will remove the interior walls to re-wire, re-plumb, and re-insulate, but that is still well into the future.
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Old 04-13-2010, 10:43 AM   #3
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Bob, I'm getting ready tp do that to my trailer. I'm using a rubber tape with adhesive backing. I don't know much about EVA, but if it provides a better thermal break than rubber, I'd be interested.
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Old 04-13-2010, 10:53 AM   #4
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a/s already has and uses a butyl double sticky thermal break tape.

it's applied between ribs and outer skin.

seems this stuff has been used on all new 'streams for 10 years or so...

i assume anyone could purchase this tape for this application.

no doubt it helps SOME with heat/cold conduction.

but it also makes for 'dimpling' around the bucked rivets.

my preference would be for a NON compressible material.

cheers
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Old 04-13-2010, 04:49 PM   #5
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This is interesting to me. I have not camped in an Airstream, and don't know anything about how hot or cool they get, whether there are condensation issues, etc. I will be doing a removal of the interior skins to revulkem seal the seams, rewire, insulate, etc. and didn't think about this. I have in mind to use the Prodex reflective insulation as mentioned in several threads.... Rae
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Old 04-13-2010, 05:02 PM   #6
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Quote:
Originally Posted by Bob Thompson View Post

Anyone game to try it on their project! I'll make you a really great deal on ready to use EVA strips, say $2 per 6' length of EVA foam with the adhesive applied and ready to use. I would cut strips to be about 1/4" wider than rib face. Let me know. I could send samples. Bob T.
I'm game, as I have been looking for some time. I will PM you with my address as I would like to check it out. Do you have a spec sheet for it.
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Old 04-13-2010, 05:18 PM   #7
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Ambi, I think the rubber (Neoprene?) and the EVA would perform equally well. I don't know of a benefit of one over the other. Some of the EVA in my stash has some neoprene mixed in with it to give it abrasion resistance and toughness. I would think the functioning of both would be about the same. The EVA might provide some weight savings as rubber can be heavy. Plus the EVA might slow the conductance of heat a bit better due to being less dense. Sorry, I don't have a spec sheet for the material.
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Old 04-13-2010, 06:30 PM   #8
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I got a 3x20 foot roll of 1/16th (0.063) dense (stiff) sheet silicone gasket material that has little or no crush to it - thinking a spray 3M adhesive or similar to lock it in place and triple-up on rivets; but I am also doubting the structural integrity of adding wiggle to the interior liners....
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Old 04-13-2010, 09:11 PM   #9
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Now, I'm no engineer (nor do I even play one on TV), but as I read this thread, I wondered if there is a meaningful break in the heat tansfer between inside and outside skins with such a thin material.

What I mean is, wouldn't there be a majority of the heat still being transferred just through radiance from the outer skin to the ribs?

Or does either the tape that AS uses now, or EVA have enough resistance in 1/16 of an inch thickness to resist all the heat wanting to move to the other metal structure?
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Old 04-13-2010, 10:10 PM   #10
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Actually aluminum has a bizarre property of little heat loss through radiance - the molecular level just does not radiate much in the infrared light spectrum.

And yes a mere sixteenth of isolation is not that much when it turns bitter cold but will extend shirtsleeves only comfort in hot and cold weather PLUS it will also help quiet the interior...
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Old 04-13-2010, 10:30 PM   #11
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What Wabbiteer says is exactly as I remember it from my HVAC classes in graduate school. Even a break as small as 1/16" can greatly reduce the conductance of heat provided the intended thermal break isn't a good conductor also.
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Old 04-14-2010, 09:43 AM   #12
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Bob,

Spartan used a thin layer of plywood between the ribs and interior of the trailer (not sure which year this started). They spent a lot of time and energy trying to improve the livability of their trailers, because people were of course living in them throughout the country.

In addition to their concerns about the aluminum conducting heat and cold into the interior, they also changed the insullation from Kimsul to the pink stuff. In fact, I believe in was around 1951 that they were experimenting with trailers up in Alaska and Florida to make improvements.

I have been thinking about using cork as a thermal barrier.

Carol
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Old 06-25-2010, 05:54 PM   #13
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As I'm getting ready to pull the inner skin from my Globetrotter, I've been thinking about this a lot and I wonder if edge banding tape would work. It is an iron on product used to cover plywood and melamine edges in the cabinet industry. It comes in various widths and is available in real wood or PVC with heat melt glue on one side.
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Old 06-25-2010, 08:02 PM   #14
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I would think the edge banding would help, but it is thin. If you decide you want to use the EVA foam with sticky tape applied, let me know. I can make up strips for about $2 per 6' piece plus shipping. I have 3 densities and thicknesses from about 1/10" to about 1.4mm.
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