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Old 11-18-2008, 09:13 AM   #1
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Insulation thickness

OK, time to replace the spun glass insulation before I reskin the inside. I found1", 1.5", and 2" at the local HVAC contractor. The gap between inner and outer skins appears to be about 1-5/8", maybe 1-3/4" max. I am leery of the 2" because I don't want to over compress it and lose insulation value, and I know that compressed insulation can create quite a bit of pressure over a large area.

Has anyone found 1-3/4" spun glass bats? If not, which thickness would you use? I'm contemplating the foil-faced bubble stuff (1/4") and the 1-1/2" glass, but that would require putting the bubble right on the outer skin--no air gap and loss of a lot of effectiveness.

I could use the 1" glass bats with the bubble, but I really don't want to get into installing the bubble stuff with an air gap--a huge pain and my insulation effectiveness tests didn't show that much advantage for that configuration over just full thickness glass.

I'm leaning toward the 1-1/2 solution. The amazing thing is that all three of these thin bats (4' by 75') are about $100 from the HVAC guys. Sheesh.

Zep
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Old 11-18-2008, 11:53 AM   #2
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OK, time to replace the spun glass insulation before I reskin the inside. I found1", 1.5", and 2" at the local HVAC contractor. The gap between inner and outer skins appears to be about 1-5/8", maybe 1-3/4" max. I am leery of the 2" because I don't want to over compress it and lose insulation value, and I know that compressed insulation can create quite a bit of pressure over a large area.

Has anyone found 1-3/4" spun glass bats? If not, which thickness would you use? I'm contemplating the foil-faced bubble stuff (1/4") and the 1-1/2" glass, but that would require putting the bubble right on the outer skin--no air gap and loss of a lot of effectiveness.

I could use the 1" glass bats with the bubble, but I really don't want to get into installing the bubble stuff with an air gap--a huge pain and my insulation effectiveness tests didn't show that much advantage for that configuration over just full thickness glass.

I'm leaning toward the 1-1/2 solution. The amazing thing is that all three of these thin bats (4' by 75') are about $100 from the HVAC guys. Sheesh.

Zep
Use the 2 inch.

It won't hurt anything, not even the "R" value.

BUT, do not use any form of backing, no paper, no foil.

The walls must breathe, from inside to out, as well as outside to in, to prevent corrosion, within the walls.

Andy
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Old 11-18-2008, 04:45 PM   #3
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I used unfaced 3 1/2" batts split in half. Worked great, and a lot cheaper.
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Old 11-18-2008, 05:35 PM   #4
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I used unfaced 3 1/2" batts split in half. Worked great, and a lot cheaper.
How did you split it? I've considered this, but thought I'd make a mess of the insulation.

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Old 11-18-2008, 05:37 PM   #5
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I used unfaced 3 1/2" batts split in half. Worked great, and a lot cheaper.
We've done the same ~

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How did you split it? I've considered this, but thought I'd make a mess of the insulation.

Zep
We just pulled it apart...it splits pretty easily - no mess.

Shari
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Old 11-18-2008, 06:16 PM   #6
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We've done the same ~


We just pulled it apart...it splits pretty easily - no mess.

Shari
Ditto. But I used the foil stuff too on the outside of the shell with spacers, but that's another story. I'm very happy with it, BTW.

What I did was to buy the 3.5" rolls of pink stuff (30 foot rolls, IIRC) from HD, remove the paper backing, then split in half. Cost was about $10.00 per roll. I think I used about 4 rolls, all totaled. It's over in my Full Monte therad someplace.

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Old 11-18-2008, 07:06 PM   #7
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On the overlander did the splitting of the R-13 (3 1/2") unfaced, worked great.
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Old 11-18-2008, 08:59 PM   #8
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The walls must breathe, from inside to out, as well as outside to in, to prevent corrosion, within the walls.
Andy

Andy, this statement has me confused. I am rebuilding a 1966 Safari. It has several leaks in the outer skin due to the use of Olympic rivets that had no sealant and missing rivets. I am busting my hump to replace these with Bucked rivets and "Vulcam" to seal up all leaks in the exterior skin. How can the exterior skin "breathe" without leaking? Am I doing something wrong making this trailer as water tight as possible? I am tired of rotten floors and stinky insulation.

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Old 11-18-2008, 09:07 PM   #9
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Alumanutz, I'm thinking you're on the right track, but since they all leak eventually, not allowing the insulation to breath means when a leak happens, the water will be trapped either above the insulation against the outer skin, or in the insulation itself. If it is unfaced, in theory it will dry out faster in the event of a leak (or humidity etc). Plus there is condensation from differences in temperature. All lead to corrosion, mold, mildew etc.
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Old 11-18-2008, 09:13 PM   #10
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Not to be a PIA, but if they will all leak, wouldn't that include the inside skin, allowing the insulation to dry out? I'm not really trying to be a smart ass but I am wondering if I am going over board with sealing this thing up?

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Old 11-18-2008, 10:31 PM   #11
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Not to be a PIA, but if they will all leak, wouldn't that include the inside skin, allowing the insulation to dry out? ...
NUTZ
I don't pretend to speak for Andy, but here's my take. IF (note the BIG if, here) you get a leak, the shell needs to dry out reasonably quickly. For any of you who have taken the inside skins off, you know the inside skin provides a very porous path to the inside of the trailer from the space in the shell. The outside is presumably tight, as in water tight. So you need to make sure there is a path from all parts of the shell to the INSIDE.

If you use bubble as your outer insulation, it should be gapped at the bottom and probably (not positive about this, which you'll see in a moment) at the top. Most of the bubble people are applying a layer of glass on the inside of the bubble layer. That glass will significantly slow any circulation of air around the loop created by the bottom and top gap, but will allow moisture to escape towards the inside. Then normal window, door, and vent operation will let the water vapor escape from the trailer.

In my opinion, the shell only breathes towards the inside (unless you've got a crappy, leaky outer shell). Except at the C channel, of course, which breathes the shell down into the banana skins and out.

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Old 11-18-2008, 11:08 PM   #12
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Man, I am confused now! Where does glass figure in? And what about gapping the bubble at the top and bottom? Where do i read about this stuff?

Help me, I've fallen down and can"t get up!!

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Old 11-19-2008, 10:18 AM   #13
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"Glass", as in shorthand for "spun glass insulation, the pink stuff."

The gaping (at top and bottom) issue is just my logical conclusion that you shouldn't create a trap for water if you have a leak in the shell. I've seen some wonderful bubble insulation installations where the sheet of bubble was carefully sealed to the ribs on all edges, which creates a potential problem because the bubble is impervious to water vapor--that creates a space with no way for the vapor to get out.

This is because of the the other gaping issue--for the bubble to be most effective, it has to have a small air gap between it and the outer shell. So you createa small air space, maybe 1/2" thick, between the bubble and the shell. Now, if you don't use the pink stuff on the inside space between the bubble and the inner skin, you can't provide a breathing gap at the top and bottom because you'd get fairly rapid thermally driven air circulation from the outer space to the inner space, defeating the insulation.

So, you put in 1/2" spacers, the bubble stuff, then 1" of pink stuff, which fills the space between the skins. You get a high insulation value from the bubble, about R 7, plus additional R value from the pink stuff, about R 3. This is the theory.

However, when I did extensive tests on various methods of insulating the shell (http://www.airforums.com/forums/f46/...sts-40442.html) I didn't find the bubble stuff to be that much better than just using full thickness glass mats. The effort required to get a good seal with the sheets of bubble insulation is significant, plus no one really has any good feedback on whether really hot days might cause the tape or glue to soften and let go, creating gaps which totally reduce the insulating value of the bubble (unless there is glass mat behind it). So I've elected to just use the tried and true Airstream method--pink stuff, full thickness.

You can save yourself a week of reading if you go to post 62 in the above thread--the Prodex (really good bubble foil) and Pink Glass both rank high (in the green part of the insulation techniques list).

Zep
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Old 11-19-2008, 03:55 PM   #14
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Zep, my apologies for hijacking the thread. I didn't mean for it to take different road. Let us know how things are coming along with the insulation.

Jim
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