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Old 07-09-2012, 11:52 PM   #1
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Highest quality insulation for total restoration?

My wife and I are amateur astronomers and we boondocks in remote areas with substantial temperature variations (from 113 degrees to 15 degrees F). We presently do this with our 1974 23' Safari. The original fiberglass insulation does not properly insulate the interior. Sleeping next to the exterior walls can be a very chilling experience!

We are thinking of purchasing a 27' to 34' 1980's or early 90's Airstream for 6 month excursions. We would remove the interior walls/ceilings during the restoration and possibly the floor.

What would be the best insulation (sprayed in foam, rigid foam, etc.)? We would prefer a non-off gasing product. What would you do to the floor and underbelly?

This is my first post since joining the forum. Thanks in advance for your replies. And I am especially interested in the experiences of those that have already actually done what we are proposing.

~jerry
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Old 07-10-2012, 12:02 AM   #2
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Probably the spray foam is going to be the best insulation for the thickness. It does have some drawbacks. If you have a leak the water gets trapped in there and if you have to fix something you have to tear out all that foam to get to it.

You could also use a rigid foam sheet and maybe a radiation barrier as well. Covering the inner skin with warm fabric will help also. My 81 has mouse fur on the walls around the bed area. Mine is a rear bedroom unit.

Get you a good sleeping bag to keep yourself warm. Just use the trailer as a big tent if you don't have the propane to keep it warm. You can get some bags that zip together if you want to get cozy with the wife. In the summer sun you can get some of that radiation barrier stuff and make a solar blanket for the roof of the trailer. Think Skylab here when they had to make a new solar reflector when a panel blew off during launch.

http://spinoff.nasa.gov/Spinoff2006/ch_9.html

Perry
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Old 07-16-2012, 11:31 PM   #3
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Perry, that was a very interesting article. Have you heard of anyone bonding that material "heatsheet" to some type of foam for structural insulation? That way it could be applied permanently to the inside walls of the trailer.

Thanks for the help.


~jerry
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Old 07-17-2012, 05:37 AM   #4
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Check out Supertherm.
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Old 07-17-2012, 07:47 AM   #5
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RMAX makes a rigid foam with foil on one side. Most home improvement stores have radiation barrier as well.

There are 3 ways for heat to be transferred. Radiation, conduction and convection. You can take care of convection by limiting voids between walls. Radiation barriers reflect heat back where it came from. They heat up because they absorb some radiation from the sun. They also use low emmisivity so as little heat as possible is radiated to the inside. Conduction is a more brute force method by putting a material between the skin and the walls that does not conduct heat well. Since the walls are thin, you are limited in thickness so a radiation barrier will reduce the heat going in the system. So Q=k (Toutside-Tinside) where Q is the amount of heat and k is the conductivity of the material. So the more you can reduce the temperature difference the less heat is going to get to the inside.

Polishing the roof or painting it white will help a lot. Putting a solar blanket up there will help a lot and having awnings all around.

Perry
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Old 07-17-2012, 08:39 AM   #6
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I used 1.5 inch rigid foam it had foil on one side but I believe it makes no difference as the AS has aluminum out and inside to reflect heat. It has an R value of about 7.5. Unless you can get better from spray in I think it's the way to go. Thermal reflective R values are very misleading. They are not true R values. Just what they can reflect if exposed to something like direct sunlight. Once you place it behind something like a wall it loses a lot of its reflective R value anyway. It's like putting a blanket in front of the widow sun shade in your car. The blanket is now doing most of the work.
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Old 07-17-2012, 07:45 PM   #7
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Timeless and some of the other shops are using:

Polyisocyanurate.

DOW Super Tuff-R

See comments by Top on this

.
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Old 07-17-2012, 08:21 PM   #8
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Insulation for houses and other buildings has changed a lot in recent years and while fiberglass is still used, it is going out of style. Airstream is far behind the times.

As Rednax says, polyisocyanate is probably the best available. I don't know if you can spray it (and that requires some knowledge of what you are doing), but it is available in board form and has pretty high R value. Any insulation has to be sealed well because even a small amount of air movement through the wall interior drops R value significantly. If I were restoring a trailer, I would use a vapor barrier between the outer skin and the insulation. To let water that condenses or leaks between the outer skin and the insulation have a place to go, I would devise weep holes at the bottom. Then I would put in foam board and seal it all around with spray foam that does not expand much (it can be hard to know which you are buying, be careful). Heat and cold move through the ribs to the interior, so a thermal break between the ribs and inner skin are necessary—materials for that are also available.

I would also add any new electrical cable you may need at some time plus you may want electronic stuff such as wiring for wifi and call boosters on the roof. For solar, best to install 8 AWG cable to the roof from a place for a solar controller and then to the converter. Once foam is in, you will not want to open the walls to install more wire.

When it is hot, a generator can be used run the A/C to cool the interior. Cooling all the solid things inside takes time, but if you don't, they will radiate heat all night. Even an hour or two will make a difference in how much heat the trailer stores during the afternoons. And go north—same stars and planets above Canada.

Fine Homebuilding runs a lot of articles on insulation. If you go to their website, you can find them in the index of all recent issues. You'll have to pay for them, but you'll learn a lot. I'm sure the publisher, Taunton Press, has a book on it too. You can see what the latest info is and adapt it to a trailer.

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Old 07-17-2012, 08:26 PM   #9
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Radiation barriers work better than you think if installed properly. The outer skin does not reflect anything unless it is polished. If polished it might reflect 90% of the sun light that hits it. If it is oxidized maybe it absorbs 50% of the light from the sun. If you have a layer of radiation barrier below the skin, 90% of that 50% is reflected back to the skin. The bad news is the skin will probably get hotter. If you have another layer of rad barrier below the first one then 90% of that heat is reflected back to the first layer. Now lets say it is winter and it is hot inside and cold outside. The process works in reverse. The heat from inside is reflected back inside. This is all great if you have a nice clean surface but what happens in a few years or months when that shiney aluminum rad barrier is dirty and does not reflect heat very well.

Perry
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Old 07-17-2012, 08:33 PM   #10
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Perry, can a radiation barrier be used as a vapor barrier too?

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Old 07-17-2012, 09:26 PM   #11
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If you seal the edges with the silver duct tape then yes. Water condensing on the aluminum coating may eventually eat it away though. Most radiation barriers are coated on both sides and the sides are insulated to some degree from each other. Prodex is thicker so the front and back surfaces are insulated from each other better than some of the other products. I believe the spray urathane foam like they use to insulate houses has the best R-value (lowest k) per inch of thickness. Avion uses this stuff. I have mixed emotions about using spray foam because it traps water. I suppose if you coated the inside with something like bed liner and then sprayed the foam you would have a good system but heavy.

I used two layers of 1/2" RMAX in my walls. I think it has an R-value of around 6. It has foil on both sides. There is an air gap between the layers. Any time you have an interface you slow heat transfer between surfaces. So two layers of RMAX is probably better than 3.2+3.2 because of the interfaces not to mention the foil. You could probably get a layer of rad barrier in there as well. The roof is the area where you want to be the most OCD about having good insulation. The support ribs bypass any insulation you put in there. This would be called a thermal short because at the ribs heat can pass from one skin to the other because aluminum is very conductive.

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Old 07-17-2012, 10:30 PM   #12
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This is what I have learned.

Heat passes by radiating UV, convection and conduction. Convection is air to air and then in conducts to a solid.

Aluminum is very good as both a barrier to radiant heat and also does not radiate heat itself very well. Silver is better but who can afford silver. It has to do with the way the metal molecules align.

Metal, aluminum, conducts heat very well.

White reflects the Sun’s energy better than shiny aluminum. Most of the Sun’s energy is visible light, not UV. It is not a coincidence that we see the Sun’s light and not UV. I white trailer top will reflect the Sun’s energy the best.

I have actually made up test and run experiments. I think this is the best solution.

First, clean the inside of both the outer and inner skins. The shinier the better (less surface area). Let me explain.
The outer shell will heat up very hot. The shiny aluminum will not radiate the heat that well. The heat will conduct to the air, convection across the space and conduct to the next solid in line. Air is a poor conductor of heat. It Is best to not place anything against the outer skin. It would then be best to put insulation between the skins to slow the air. A insulation in the center as thick as possible but not touching either skin. Seal off all gaps with foil tape. This may be easiest with bubble foil held off the skins by small foam blocks. I think next best is a foil held off the outer skin by small foam blocks and fiberglass after that. I think fiberglass is better than rigid foam as you can fill in voids better.

Another thing is to somehow isolate the ribs from conducting heat from the outside skin to the inner skin. This is probably the single most contributor to heat transfer. Put a layer of very thin, non conducting material on the rib before you place the inner skin back on. Do not put too thick of barrier as this may reduce the effect of the inner skin provided strength if it is “floating”.

Painting the inner skin, the side facing you, allows for heat radiation. Leaving the aluminum bare and polished would be best.

Also, the shape of the trailer works as a parabolic dish at you. Hold up a piece of aluminum in the sun and just the slightest bend you will notice the increase in heat. The curves in your trailer do the same.

A light sheet will help you stay cool at night if the ceiling is hot. It will block the radiant heat some.

A sleeping bag in the winter would be better. The skin will always be cold and will conduct heat away from you readily.

Of course I learned most of this after I insulated my trailer but could not get it to cool in the Texas sun. I used rigid foam then bubble foil. I think I have it backwards. I will change it if I ever have the inside out again.
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Old 07-18-2012, 07:40 AM   #13
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The white and the aluminum absorb about the same amount of heat from the sunlight but the emissivity is higher in the white paint so it radiates the heat much better than aluminum. I have measured these properties before. The absorptivity is the amount of heat energy absorbed from the sun which is mainly visible light. This is about 90% for white paint and polished aluminum. The emissivity or IR reflectance of aluminum is probably not very good. The emissivity of white paint is better and that is why it runs cooler. It radiates more of its heat energy away. See this table. It is the ratio of these two values that determines the heat that goes into your trailer. Convection plays a part as well but the sunlight is a BIG factor. You want low absorptivity and high emissivity.

I use to test space station paints and coatings by measuring these properties and then expose them to UV radiation and measure these properties again after UV exposure. These properties are important for thermal control of spacecraft.

Take a look at this chart of the thermal properties of different materials and paints.

http://www.solarmirror.com/fom/fom-serve/cache/43.html

It is the ratio that makes the white paint so good. The ratio for aluminum is like 3 and the ratio for white paint is like .22. The problem with white paint in the southeast is it mildews pretty fast. The lower the ratio the cooler it is going to run in the sun.

So the best roof coating is white if you can keep it that way. The best wall coating on the inside is bare aluminum in the summer.

The sun puts out about 1400W/m2 in space. By the time it gets through all the crap and moisture in the air, you are probably at about 1000 W/m2 at noon. Multiply by the cosine of the angle of the sun to get the actual value. So that means that you could be getting 1000W of heat per square meter of roof area. 1000W (5000 BTU) is about the heat output of a space heater. So there are several 1000W of heat you have to deal with and you might be able to remove about 10,000 BTU of that with the AC. Windows are a big source of heat absorption as well. Whatever comes in the window is going to end up as heat.

Perry
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Old 07-28-2012, 08:31 PM   #14
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Perry, how did you apply those two layers of RMAX to the walls of your trailer, and what would you apply to the windows to make them more efficient?

And thanks to everyone for your comments and help!

~jerry
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