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Old 01-15-2018, 08:35 PM   #1
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Default Insulation

Wondering if anyone has info on just how the major Class B mfgs handle insulation ? I came across the Youtube channel of an HVAC / mechanical engineer in the UK that's building his own, and for the first time really understood just why you insulate a van in a certain way. Esp. important was his use of Reflectix. Not as insulation (it's poor at that), but as a vapor barrier to keep the actual insulation dry. Thus preventing condensation forming on the inside of the cold outer steel wall and potentially causing corrosion.

https://www.youtube.com/user/sliderno1/
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Old 01-15-2018, 09:03 PM   #2
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I don't see any evidence of any isulation in a 2003 Roadtrek. There is a bit of it on top of the refrigerator to keep burner heat out of the cabin. Other than that there isn't any. None between the wall panels and body. None in the floor other than carpet. None in the roof.

Heat shields were placed around the exhaust system here and there but plastic pipes melted anyway.
Harry 2003 C190P
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Old 01-15-2018, 09:44 PM   #3
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Esp. important was his use of Reflectix. Not as insulation (it's poor at that), but as a vapor barrier to keep the actual insulation dry. Thus preventing condensation forming on the inside of the cold outer steel wall and potentially causing corrosion.
In all respect, this is nonsense. The first rule of insulation is "only one vapor barrier." In a home, you put it either inside or outside the insulation, depending on climate. In a van, you have no choice: It came with a near-perfect vapor barrier on the outside. You MUST NEVER add one on the inside, since moisture will be introduced between the two barriers via fluctuations of barometric pressure, and it will never dry out. It will be trapped there forever. If you could make a perfect vapor barrier, that would be a different matter, but you can't. If nothing else, the weep holes built into the bottom of the van would defeat this effort. For this reason, it is vital that insulated areas be provided with some amount of ventilation. There is such a thing as a "vapor retarder", which can help with the problem that the guy in the video seems to be worried about, but it is quite different from a vapor barrier.

This is a common error by over-enthusiastic DIY insulators. I even know of one small professional upfitter that at least used to do it. But it is unambiguously wrong, as any insulation professional can testify. Here is one good discussion:

https://buildingscience.com/document...vapor-barriers
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Old 01-15-2018, 09:45 PM   #4
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Originally Posted by dhuff View Post
Wondering if anyone has info on just how the major Class B mfgs handle insulation ? I came across the Youtube channel of an HVAC / mechanical engineer in the UK that's building his own, and for the first time really understood just why you insulate a van in a certain way. Esp. important was his use of Reflectix. Not as insulation (it's poor at that), but as a vapor barrier to keep the actual insulation dry. Thus preventing condensation forming on the inside of the cold outer steel wall and potentially causing corrosion.

https://www.youtube.com/user/sliderno1/

I have watched the video.

He could have used Tyvek as vapor barrier. No need to use Reflectix.
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Old 01-16-2018, 12:06 AM   #5
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I was wondering about using Tyvek. Dunno how avail it is in the UK. We certainly have it installed on my house
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Old 01-16-2018, 12:16 AM   #6
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Tyvek is made to stop water, but pass water vapor, so it can be used on the "wrong" side of a wall to help keep it from getting wet and to stop the wind from getting in. Since neither side of the insulation gets water on it, I don't think it would do much good, or bad.
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Old 01-16-2018, 12:20 AM   #7
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.

I have forgotten Tyvek allows vapor.
I guess that's not good.

How about plastic sheet?
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Old 01-16-2018, 12:26 AM   #8
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.

I have forgotten Tyvek allows vapor.
I guess that's not good.

How about plastic sheet?
No. it is good. If you insist on putting some kind of sheet material between your insulation and wall sheeting, then Tyvek might be a good choice, since it would not trap moisture. As Booster said, probably won't help much, but it won't hurt either.

Plastic would be a terrible idea.
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Old 01-16-2018, 12:52 AM   #9
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No. it is good. If you insist on putting some kind of sheet material between your insulation and wall sheeting, then Tyvek might be a good choice, since it would not trap moisture. As Booster said, probably won't help much, but it won't hurt either.

Plastic would be a terrible idea.
Ok Thanks.


Why is plastic bad?
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Old 01-16-2018, 12:58 AM   #10
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Tyvec is good to protect the wooden shell until siding is put on. I have removed 20 yrs old siding with Tyvec applied underneath. The Tyvec was ripped, fibers were degraded. IMHO a was of money if used to create a permanent wind or vapor barrier.
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