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Old 04-26-2006, 09:49 AM   #225
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Originally Posted by uwe
... It does seem that it has better heat reflection,if that is possible.
well, yeah. thats what its supposed to do. while fiberglass slows heat transfer in an entirely different way. Fiberglass slows down "conduction", while foil reflects radiant heat. If you google around on "r-value", you'll find that (at least according to the people that pedal this stuff), it is an innacurate measurement of a given material's insulating ability. kind of reminds me of trying to measure strawberries by the cup. (hard to measure irregular shapes by volume). Anyway, I think you'd also find the same sort of disclaimers if you look closely at fiberglass's labelled r-value...its a number derived in a lab that doesn't factor in real-world conditions, like the fact that air can blow right through it. (air doesn't move through it in a lab test...but it does in your house). so the r-value is really only of any use when comparing a type of insulation to itself; i.e. 3" of fiberglass vs. 6" of fiberglass.

What would really be neat would be fiberglass batts with a foil-bubble backing. but that would probably be impractical to make. But then you'd get the best of both worlds (sound deadening of the fiberglass).
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Old 04-26-2006, 10:21 AM   #226
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Quote:
Originally Posted by chuck
What would really be neat would be fiberglass batts with a foil-bubble backing. but that would probably be impractical to make. But then you'd get the best of both worlds (sound deadening of the fiberglass).
Actually, foil bubble with 2-sided fiberglass backing would be just about the cat's meow for insulating Airstreams...take care of the much needed Airspace plus the advantage of sound deadening. However, it would add the loose fiber issues and the absobing nature of that fiberglass again.
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Old 04-26-2006, 10:22 AM   #227
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Originally Posted by chuck
well, yeah. thats what its supposed to do. while fiberglass slows heat transfer in an entirely different way. Fiberglass slows down "conduction", while foil reflects radiant heat.
I was thinking along the lines of heat vs.cold, actually. My feeling was that it might reflect heat better than cold. If that's even possible.....
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Old 04-26-2006, 11:16 AM   #228
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I'm not very happy with the idea of fiberglas on one or both sides of the bubblefoil material. The foil needs to "look" at the surface across the air gap in order radiate (or reflect) heat to it.

Fiberglas does not insulate by slowing down heat conduction, it works by preventing convective heat flow.
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Old 04-26-2006, 11:28 AM   #229
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Jim and Uwe, I certainly see some advantages as well, but we have such extreme temperatures here in Arizona (110 all summer in the city, below freezing in the mountains in the winter) that I think I need something with a higher R-value. I'm thinking an R-value of 30 is approximately what I would need. For homes built in this area, it is recommended that attics have an R-value of at least 38. I imagine it's the same for very cold climates as well. That can be accomplished through fiberglass insulation, but it's very thick; approximately 9". Of course as you know the walls of the Airstream have about 1.5" of space. I don't know if the compression negatively affects the insulation or not.

However, I've done some research and learned that the foil type insulation is supposed to provide a different type of insulation; a radiant barrier in that it reflects heat energy instead of trying to absorb it, whether keeping heat in or out (since it reflects on both sides). Also, foil insulation does not decrease in effectiveness if there is an increase in humidity. While R-values measue conductive heat, radiant heat is not taken into account which is primarily what foil insulation protects against.

I think what I'm going to do is use a standard fiberglass R-30 insulation under the floor, stapled to the bottom of the plywood. This is most cost effective and there is room for it down there. For the walls I'll probably go with a hybrid approach, using a thin fiberglass insulation combined with the foil insulation. I may actually use two thin layers of fiberglass insulation in front of and behind the foil insulation in lieu of an airspace.

There's an interesting foil insulation called "Prodex FfmF" which sandwiches foam between the foil layers. It has an r-value of 14.5. I think i might put this between two layers of a thin R-13 fiberglass insulation. I guess that would give me an R-value of around 40.5, if I can fit it all in the walls.
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Old 04-26-2006, 11:41 AM   #230
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Originally Posted by markdoane
I'm not very happy with the idea of fiberglas on one or both sides of the bubblefoil material. The foil needs to "look" at the surface across the air gap in order radiate (or reflect) heat to it.
Mark, that doesn't make a lot of sense to me. If fiberglass is ineffective against radiant heat anyhow, why couldn't it be used as the airspace around the foil? To the foil and to the radiant heat, the fiberglass is essentially "invisible' anyhow, so it should be able to "look" right through it...

Am I missing something? (I often am!)
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Old 04-26-2006, 12:01 PM   #231
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Originally Posted by ankornuta
I don't know if the compression negatively affects the insulation or not.
it does. by alot, from what I understand. we're mixing measurements again.
Fiberglass's insulating qualities are not based on mass or weight alone, but its volume, as well. I read somewhere that if you compress fiberglass batts, you'll wind up with insulation that is even less effective than a thinner batt in its factory state. that is, a 12" batt stuffed into a 6" space will not insulate as well as a 6" batt. its the "fluffiness"...(F-factor? ) the amount of trapped air in there (volume) as well as the amount of fiberglass (mass or weight). so trying to stuff a 9" batt into a 4" floor cavity will be self-defeating.

Uwe: I'm no scientist, but my understanding is that you can't "reflect cold". heat=energy; cold is the absence of that energy. something like that. anyway, heat always moves toward cold.
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Old 04-26-2006, 12:10 PM   #232
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Thanks Chuck. I'll have to re-think some of my ideas regarding using a 9" thick R-30 for the floor then. Here's a simple question in regards to insulation compression; when insulating the floor, is the insulation only placed between the cross members, or is it placed over the top of all of them? It seems to me that the best approach would be to only go between the cross-members, but I'm curious what others have done.

Quote:
Originally Posted by chuck
Uwe: I'm no scientist, but my understanding is that you can't "reflect cold". heat=energy; cold is the absence of that energy. something like that. anyway, heat always moves toward cold.
In regards to the above, foil insulation primarily only reflects heat. The idea is that if heat is generated inside of a structure, it will keep that heat in. If heat comes from outside the structure, it will keep that heat out. That's my understanding of it...
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Old 04-26-2006, 12:56 PM   #233
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Originally Posted by ankornuta
when insulating the floor, is the insulation only placed between the cross members, or is it placed over the top of all of them? It seems to me that the best approach would be to only go between the cross-members, but I'm curious what others have done.
well, what the factory did was lay out the batts on top of the frame, then squished it down with the floor. the fiberglass obviously got compressed by the x-members, but remained "fluffy" in the cavities. I've seen people here post various ways of getting the stuff to stay up in the cavities from below...lots of ideas. some used straps of some sort to hold it in there. I think this is why (at least in part) some people went with rigid foam. its easier to attach.
Quote:
Originally Posted by ankornuta
In regards to the above, foil insulation primarily only reflects heat. The idea is that if heat is generated inside of a structure, it will keep that heat in. If heat comes from outside the structure, it will keep that heat out. That's my understanding of it...
yep, that's what they say.
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Old 04-26-2006, 05:51 PM   #234
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Unless you can get aircraft grade high density glass I think you would be better off with foam board. Here's what I did. Some over kill and some other than idea application of product.

1) I painted the underside of the floor with microshere reflective insulating paint.
2) Over the frame I put a layer of two sides foil bubble wrap which have random small bubbles with a thickness of 3/8 inch. I taped all seams.
3) I put pink 2" foam sheets between frame members very snuggly and used foam for any gaps. This left about and inch above the sheets and an airgap for the foil. I have an oversided furnance so I was more interested in keeping the heat for the 120 deg highway out than the heat in.

I used a similar system in the walls. Same bubble wrap and thinner foam sheets. In some areas no foam, rather an air gap on each side and sealing all edges to prevent airflow. I glued the foil to the top of the end caps. There isn't as much space between them and the outside shell as with the walls. I also lined the inside shell with 1/8 inch closed cell foam and then covered it with another layer of .1672 T3 aluminum.
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Old 04-26-2006, 06:58 PM   #235
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well, what the factory did was lay out the batts on top of the frame, then squished it down with the floor. the fiberglass obviously got compressed by the x-members, but remained "fluffy" in the cavities......
Here's a pic of what Chuck is talking about. See how the frame members compressed the bats? Just for the record, this type of insulation in the belly pan is a real mess. Dust, dirt and water get in there, it seems almost inevitable. It looks so bad (and smelled so bad) that I won't even post pics here of some of the areas under the floor.
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Old 04-26-2006, 07:19 PM   #236
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Sorry, I got distracted watching Mythbusters on Discovery Channel. They're trying to squash a compact car between two Semi's.

Over59, do you have a thread that describes in detail how you did your insulation? Sounds cool (no pun intended).

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Old 04-26-2006, 08:50 PM   #237
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http://www.airforums.com/forum...tml#post229373
General rehab thread. The post below give the details. If you have some specifc question I would be glad to share.
The is not a mouse freindly environment. Also nothing to hold onto water that may get in. Not in the walls or belly pan. Why an engineer would put sponge in the walls of a trailer is beyond comprehension.
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Old 04-26-2006, 09:43 PM   #238
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I love the sponge analogy. COmpletely apropos. Thanks for the link.

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