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Old 01-16-2018, 01:07 AM   #11
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Why is plastic bad?
Because it doesn't let the insulated area breathe, so it would trap moisture.
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Old 01-16-2018, 01:14 AM   #12
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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
Exactly, a common topic in DIY community, and unfortunately not always supported by facts. As already stated making a water vapor barrier inside a van is practically impossible. We generate about a pound of water vapor per night/person, so for 2 it is almost a 1/2l. If vapor barrier is not perfect this water will diffuse into insulation and time of staying there will depend on hydrophobic quality of insulation and inhibiting water vapor diffusion internal barriers.

Another mistake is use of hydrophilic insulation, worse from all is denim/cotton, easy to sell on its nice to touch petting characteristics but it soaks water and loves to keep it. I think Advance RV used or is still using cotton based insulation, for their price must be a “hydrophobic cotton from Alaska”.

Another one is misuse of Reflectix, it is a great product to reflect IR – Infrared Radiation/heat. IR can pass through air, through IR transparent plastics, quartz, special glass, silicon - all to different degrees. If IR is blocked from Reflectix it no longer works as intended, so an IR transmitting air gap is necessary for Reflectix to work.
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Old 01-16-2018, 02:25 AM   #13
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.

ARV does not use denim anymore.

BTW the recycled denim is treated for water and insect and mold resistance.
OK I hear you... the chemical can wear out and it will become hydrophilic again.
And people have found insects in them after a few years.

Disclaimer: I have no first-hand experience one way or the other.
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Old 01-16-2018, 03:14 AM   #14
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Boric acid and ammonium sulfate are both soluble in water which will not give the Denim insulation hydrophobic quality, just bug resistance. In addition, it could produce a perfect electrolyte to help chewing van’s steel walls from inside out. Oops.
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Old 01-16-2018, 03:41 AM   #15
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Boric acid and ammonium sulfate are both soluble in water which will not give the Denim insulation hydrophobic quality, just bug resistance. In addition, it could produce a perfect electrolyte to help chewing van’s steel walls from inside out. Oops.

Oh no
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Old 01-16-2018, 10:58 AM   #16
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[QUOTE=dhuff;66594]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.

Because of positive negative pressures whether created by weather or on the hwy. Unless it is sealed so if 3' underwater its not sealed to prevent air exchange. I pulled my 2015 ERA 70A apart to inspect behind the panels. No wall, floor, insulated panels in the roof. The rear doors of the Sprinter sounded like a tin can with nuts and bolts when it was closed. It was the ABS plastic panel. I added fiber glass as for sound isolation and energy saving. Behind the galley the outside wall had no insulation or sound deadening. I added a closed cell insulation again for sound isolation and energy saving. Working as I have time adding sound isolation and energy saving in other exterior cavities.
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Old 01-16-2018, 05:11 PM   #17
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You could consider Thinsulate in lieu of fiberglass easier to weave/pack through difficult to access places. Using electricians’ trick of using vacuum to pull a lead line with a piece of paper on the end and use the line to pull the Thinsulate. A lot of DIY folks use Thinsulate, it became a prime material for insulation as well good sound barrier.

My van is fully insulated with Thinsulate with all glass windows and the Espar D2 (2.2 KW) has no problem keeping us warm in frigid weather. For floor I am using ¾” factory passenger van corrugated floor with ¼” SpaceAge Versatile Series Thermo-Lite board on the top plus heavy linoleum.

I started my van conversion in 2013, and the following video prompt me to dive deeper into the Thinsulate resulting in selecting it. In 2013 this material was difficult to get, I found one marine store which had a large roll in stock, used ½ if it and sold the other half. Today it is reasonably easy to get.
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