How much do I need to insulate?

[Guy]

This a great site for foil insulation. They are the least expensive I have found and their product is great. If anyone in Southern California wants to go in on some together and lower the cost sgnificantly send me a note.http://www.insulation4less.com/default.asp

[fasttimes]

You have three type of heat transfer: Conduction, convection, and radiation.

Regular insulation works at stopping conduction and convection. Radiant barriers only work at stopping radiation.

In order for a radiant barrier to work, they need an air gap on both sides. The reason for this is that otherwise without this air gap they will just transfer the heat to the next layer via conduction.

Forget the radiant barriers. Having your trailer white will reflect 90% of the suns heat (vs 97% for properly installed radiant barrier) and use foam insulation to slow down the remaining 10% of the heat that makes is past.

[Dave Nathanson]

So it seems that everybody who mentions anything technical about the aluminized bubble wrap insulation is always talking about keeping heat OUT, as if getting too hot because of sunshine was a big problem. And I'm sure that in the summertime, in hot climates like Arizona and even my local So Calif deserts it could be.

But that's not my main insulation concern. I'm trying to figure out how or IF all this radiant heat reflection will help keep a teardrop trailer warmer inside. Is it just the sealed air bubbles that help keep a teardrop warm, even more than the "radiant barrier"? Do humans product radiant heat? I dunno, but I doubt it.

I'm interested to hear Dawn's report of how her garage is a lot warmer since installing the bubble wrap on her door. That's something that I can easily understand!

http://www.insulation4less.com/insulation.asp
This stuff has an R value of 14.5 and it's only 1/4" thick. Sounds good doesn't it? Or does it? They say it compares well to much thicker fiberglass house insulation. I'm so "unclear" on this that I wrote that company an email asking for some clarifications. It's all so confusing!

Has anybody actually used the Aluminized bubble wrap insulation for a TearDrop like situation? If so, how good is it? How does it compare against other insulation types at keeping the body heat in?

[asianflava]

Forget the radiant barriers. Having your trailer white will reflect 90% of the suns heat (vs 97% for properly installed radiant barrier) and use foam insulation to slow down the remaining 10% of the heat that makes is past.

Would the aluminum exterior skin reflect the radiant heat?

[mikeschn]

Here's a quote from Rik Keller that talks about the different colors and radiant heat...

As background, remember that heat is tranferred in three ways: radiation (think sun's rays), convection, and conduction. When we're talking about solar gain on a trailer, radiated heat from the sun that is absorbed by the surface (skin) is then transferred via conduction to lower layers. The cooler the surface stays, the less the heat gain on the system. Insulation will also help keep the interior cooler (or less hot) longer by slowing the rate of heat transfer through the roof/wall.

When looking at how hot any given material gets in the sun, there are two main factors to consider. The first is the reflectivity of the material. The second is how quickly it can radiate heat off of its surface back into the air; this factor is called emissivity. Both reflectivity and emissivity are based on the surface properties of the material.

Speaking about the first point, reflectivity, aluminum (or any metal) will reflect a lot of the solar energy radiating on it. And the shinier the metal, the more it will reflect. But a white surface will also reflect to a large degree, usually more than the metal. Solar reflectance of a white surface can get as high as 0.85, meaning it reflects back 85% of the solar radiation. This is about the same as highly polished aluminum. Mill finish aluminum has a value more like 0.6, depending on the oxidation level. Also, generally, the darker the color of a material, the less reflective it will be. This is why, given the same material, the darker color will get hotter (however, there are exceptions, including some new paints that have ceramic particles embedded and are almost as reflective in darker colors as in lighter.).

So, the higher the reflectivity, the longer a material will take to heat up when exposed to a given amount of solar radiation. But that's only half the story.

The second factor is the emissivity of the material. The higher this number is, the faster the material can radiate heat that is has absorbed back into the atmosphere (different wavelength than the incoming solar radiation). Most materials have an emissivity of around 0.8 to 0.9, meaning they emit 80% to 90% of their heat. Bare metals (including aluminum) are an exception, with low emissivities that range between 0.05 to 0.6 depending on the type of metal, and its surface finish and condition. And the shinier the metal, the lower the emissivity. Highly polished aluminum has an emissivity of about 0.05. Even highly oxidized aluminum's emissivity is only about 0.25. So, even though they're reflective, metal surfaces tend to get hot since they're unable to emit away even the modest amount of solar energy they do absorb (hence "Cat on a Hot Tin Roof" or cat on a hot trailer roof!).

The ideal material, if one wants a surface that doesn't get hot in the sun, would be one that has a high reflectivity and high emissivity.

White paint does the job nicely. This is why bright white elastomeric coatings are increasingly being used for "cool roofs" that significantly reduce heat gain and hence cooling bills for buildings.

As it turns out though, a coating on aluminum, whether it is anodized, or a clear coat sprayed on, can increase the emissivity of the aluminum tremendously. Clear anodized aluminum has an emissivity of 0.76-0.84 (depending on the thickness of anodization). A clear coat would be similar, depending on thickness. Of course, white painted aluminum could have even higher emissivity (and would have a higher reflectivity). Bare mill-finish or polished aluminum, though, is going to get really hot in the direct sun.

So what kind of difference does it make in reality? The Lawrence Berkeley National Laboratory did a study on roof materials (http://eetd.lbl.gov/CoolRoofs/) and found the following average temperature gains above ambient temperatures in full sun and no wind (a 40°F gain on a 100°F degree day would equal 140°F surface temperature):

Bright white smooth materials: 15°F
Rough white surface: 35°F
Very light (pastel) colors: 15 to 55°F
Bare aluminum: 48°F
Medium gray (reflectance half way between white and black): 52°F
New, bare galvanized steel: 55°F
Intense but not very light colors (green, red, blue, etc.): 79 to 83°F
Black materials: 90°F

So on a day with an air temperature of 90°F, you could expect a clean white trailer roof (Filon, painted aluminum, painted wood, etc.) in the direct sun to reach a surface temperature of 105°F. A non-coated, non-anodized aluminum roof would reach a surface temperature of 138°F, and a black roof would reach a surface temperature of 180°F!

The lower the heat load from the skin, the less your cooling needs are in the trailer and the more effective your insulation will be.

Rik

BTW, the original thread is here if you want to see the related posts...
http://tnttt.com/viewto ... urface#309

Mike...

[Arne]

Short long story:

I was motorcycling with a friend. While waiting for a ferry, we set our helmets on the seat. Hers was white, mine was black. Her helmet was cool to the touch, mine was almost too hot to touch....

When I got home, I painted my helmet white......

-----

On our trip down south, even in the middle of the afternoon, the inside of our white tear was quite comfortable....... Humid, but cool...... (I'm working on the humid part this spring)......

[SteveH]

After reading what Mr. Keller has to say, I think even if I cover my tear with aluminum, I'll also paint at least the top white.

[Dave Nathanson]

Hi, I got an answer from the manufactor/vendor of that Hi-R bubblewrap insulation.

I asked:

I saw your website:
http://www.insulation4less.com/insulation.asp
and I have several questions about your products.

I have a small "TearDrop" camping trailer. It is uninsulated & unheated. I'm wondering if your "Hi-R insulation wrap" might be a good retrofit for my trailer ceiling.

The construction of the trailer ceiling is 3/8" plywood, covered with 0.050" unpainted aluminum sheet. In case it helps describe the application, you can see photos of my TearDrop trailer at my website;
http://TD.RoughWheelers.com

I'm unclear if the reflecting of 97% of radiant heat will be helpful in my situation or not. It is a unheated area. I am unclear about the mention of "Heat flow direction is down, emmitance of the foil surface is 0.03 & 42 mm airspaces." Does that mean that it will not do well as a roof insulation in the winter? I mostly want to keep the heat in.

Do you think that the Hi-R bubble wrap is a suitable insulation for a camper? If not, can you suggest something? Thanks.

I would like to cover this insulation with a 1/8" layer of oak paneling. Or is it important to not cover it so it can reflect properly?

Is is ok to glue this material to wood? What glues would you recommend? Can I use ordinary construction glue?

If I use 2 layers of this product, will it work twice as well? I have slightly less than 2 inches of space to work with. It's an open beam ceiling, and I would like to still see the beams.

I know I'm asking a lot of questions, but I sure would appreciate it if you could answer them! I can relay your answers to our community of builders.

Thanks,
Dave Nathanson

And the reply came back:

High R Double Sided would work well in keep the structure cool in summer and warm in winter.
Any construction glue would be fine. You might want to nail it.
1 layerof insulation is recommeded. 2 doesn't double the value.
Panel over it would be fine.
--
http://www.insulation4less.com

Well, so there we have it.

[fasttimes]

Dave Nathanson
And the reply came back:

High R Double Sided would work well in keep the structure cool in summer and warm in winter.
Any construction glue would be fine. You might want to nail it.
1 layerof insulation is recommeded. 2 doesn't double the value.
Panel over it would be fine.

Well, so there we have it.

Well, good luck. But you are probably not going to be real happy with the results, but it will be better than your current situation of totally uninsualted. Report back on how things work out for you. If it works well, I might add it myself.

[fasttimes]

After reading what Mr. Keller has to say, I think even if I cover my tear with aluminum, I'll also paint at least the top white.

They have that stuff already painted too.

[andysbunny]

I realize that the High R brand boasts over 14 in r value, but the stuff I bought (Reflectix brand) I got at Lowes for $25 a roll for a 4'x25' roll.

I just used the bubble wrap insulation for the door on my garage. It has really helped keep the heat in from my Kerosene heater. I have a thermometer on the wall in the garage. Before the door was insulated (just the walls were at the time, no windows and attached to the house.) I would go out and it would be 20 outside, 35 in the garage. After the bubble wrap insulation was put in the doors, I would go out and it would be 45 - 50, and after 30 min with the heater on low, it would be 65 -70.

It only boasts an r value of 4, but I think the previous post by me speaks volumes of it's effectiveness. I actually can work out there without being bundled up, which is great both for my woodworking, ebay "warehouse" area (part of my business) and artistic painting for school (I plan on some neat decorations for the outside of the TD when it's thru!)

If you need 700 sq ft, Or, if you need it for the garage like I did, go for the HIgh R. It does save money, but it seems like I would have a lot left over. I think it may be just as good to go to Home Depot or Lowes and get the smaller roll of Reflectix and use just what you need.

[Guy]

Dawn or Andy,

Lowes' site lists the 4'x25' for 46.74, was it on sale when you bought it?

[andysbunny]

Sorry, I am an idiot. I was looking at the 2' wide stuff!

Ain't edumacashun great?

Dawn