Class B Insulation

[Davydd]

ARV uploaded a video, "What we know (and don't know) about van insulation." It is a rundown of the insulation systems they have installed in their vans from fiber glass (maybe initially because they weren't using it in 2015) to recycled blue denim, to wool, to Thinsulate. I have blue denim installed in 2015. The wool was a special request of a customer. They pretty much have settled on Thinsulate. They didn't touch upon spray foam but they have done it and found it wanting for many reasons. Keep in mind their knowledge extends to buying back their vans and refurbishing them and performing most of the work of customers in their shop. I know that I have seen my blue denim after a couple of years and their wasn't anything wrong with it.

https://www.youtube.com/watch?v=nwhIRugx5NY&t=636s

[Davydd]

To further expand on spray insulation which wasn't covered in the video. I know they found it was not easy to install and distorted the metal skin with expansion. It is somewhat permanent in that it can't be easily removed for repairs and getting to the extensive wiring in a van. It has an R-value better than the other insulations but with metal structural conduction and large expanse of windows it probably doesn't make a hill of beans difference.

[GeorgeRa]

I purchased 90’ roll of Thinsulate in March of 2013 from a Marine outlet in Washington, sold the left-over half to Hein, active member on the Sprinter Forum. Hein took this as opportunity and became a major reseller of Thinsulate for Mercedes, Ford, Dodge DIY communities. This was one of the best decisions for our conversion. A running polling chart on the Sprinter Forum shows Thinsulate leading position from all other types of insulations.

Solar panels are often missed as excellent insulating components. Old technology of tropical/safari double roofs on Land rovers and other tropical vehicle is a good proof that they work. A well vented double steel roof with 1-inch gap blocks direct sun exposure.

[TygerMark]

Originally Posted by Davydd

....spray insulation.....is somewhat permanent in that it can't be easily removed for repairs and getting to the extensive wiring in a van.

I would not have a van where the wires are run inside of channels. In my opinion, the best van builders refuse to do this, for obvious reasons.

Best to run the wires in looms inside the van space. Always accessible and not susceptible to abrasion.

[Ray B]

Originally Posted by Davydd

ARV uploaded a video, "What we know (and don't know) about van insulation."

Excellent and Interesting Post! Great Information in this Video!

Ray Brown
2012 Pleasure Way Plateau TD
Ormond-by-the-Sea, Florida

[avanti]

When installing insulation, one must NEVER install two vapor barriers. This is just as true in an RV as it is anywhere else. This fact can be confirmed in any standard text on insulation. I guess ARV moving to "we don't know" is at least a little progress.

A good vivid example of what happens with two vapor barriers is a sealed double-glazed window with a broken seal. This is what happens:


Fluctuations of barometric pressure pump damp air into the space between the two barriers and it can never get out again. The same thing will happen in the space between the wall of the van and any added vapor barrier. An added barrier cannot be perfectly-sealed, if for no other reason than the presence of weep holes at the bottom of the van. This is beyond dispute and it is silly to argue otherwise.

[Davydd]

The outer metal skin can be said a true vapor barrier which you can't get away from in a van. Anything you put inside is a vapor retarder not a vapor barrier. Retarding is a good thing. As you said, weep holes in the bottom are there. The less moisture you need to weep the better. You can't compare a moving van with a stable in place building to determine what you need to do.

I think the main thing they discovered is arguing about what insulation is better is a fool's game in light of thermal conduction through the frame ribs, the low insulation allowed by the thickness and the overwhelming glass. That is probably why ARV settled in Thinsulate as their standard I think because it is the easier to install. It is lighter in weight I gather than wool or blue denim. I think the key to their system is the 100% Hushmat coverage as it is a great sound proofer and the real barrier of condensation on the inner metal skin. BTW, in a 144 WB Sprinter they install 100 lbs. of Hushmat and 24 lbs. of Thinsulate.

[avanti]

Originally Posted by Davydd

The outer metal skin can be said a true vapor barrier which you can't get away from in a van. Anything you put inside is a vapor retarder not a vapor barrier.

This is true in a strict sense, but as a practical matter, it is irrelevant. Permeability can be and is quantified, and different levels of permeability are well-defined in building codes. Barriers such as extruded polystyrene and elastomer coatings (among others) are classified as "Impermeable" and for all practical purposes serve as vapor barriers and can cause great harm when misused. To say that "there are no vapor barriers" ignores standard definitions in the building trades, as you certainly know.

Retarding is a good thing. As you said, weep holes in the bottom are there. The less moisture you need to weep the better. You can't compare a moving van with a stable in place building to determine what you need to do.

Yes, you most certainly can compare a moving van with a stationary structure for this purpose. Just try putting a mis-sealed double-pane window in your van for awhile and see what happens. If the vehicle spends time in a locale where there is any appreciable humidity, the problem will occur.

Retarding is not a good thing if it traps moisture, as it always does in the presence of double vapor barriers. A video from the Internet, even one made by a respected upfitter, does not change the laws of physics.

We have been through all this before. I emphasize that I am simply reporting best practice and reasoning from well-understood physics. I have provided many citations in the past. Here is a particularly fascinating review of the misuse of vapor barriers:

https://www.buildingscience.com/docu...iers#Quir_1985

Teasers:

Incorrect use of vapor barriers is leading to an increase in moisture related problems. Vapor barriers were originally intended to prevent assemblies from getting wet. However, they often prevent assemblies from drying. Vapor barriers installed on the interior of assemblies prevent assemblies from drying inward. This can be a problem in any air-conditioned enclosure. This can be a problem in any below grade space. This can be a problem when there is also a vapor barrier on the exterior.

The history of cold climate vapor barriers itself is a story based more on personalities than physics. Rose (1997) regales readers of this history. It is frightening indeed that construction practices can be so dramatically influenced by so little research and reassuring indeed that the inherent robustness of most building assemblies has been able to tolerate such foolishness.

[GeorgeRa]

Originally Posted by avanti

When installing insulation, one must NEVER install two vapor barriers. This is just as true in an RV as it is anywhere else. This fact can be confirmed in any standard text on insulation. I guess ARV moving to "we don't know" is at least a little progress.

A good vivid example of what happens with two vapor barriers is a sealed double-glazed window with a broken seal. This is what happens:

Fluctuations of barometric pressure pump damp air into the space between the two barriers and it can never get out again. The same thing will happen in the space between the wall of the van and any added vapor barrier. An added barrier cannot be perfectly-sealed, if for no other reason than the presence of weep holes at the bottom of the van. This is beyond dispute and it is silly to argue otherwise.

Interesting point, Thinsulate without an additional membrane begins to prevail in DIY community, but physics by feelings are still rampant. Double vapor barrier and hydrophilic vs hydrophobic qualities are often misunderstood. Feeling takes over, wool is nice and soft so is Denim.

I agree, stating "we don’t know" by ARV is a progress. Good news is that fiberglass insulation is not used and mineral wool insulation is used rarely.

[Davydd]

Originally Posted by avanti

Yes, you most certainly can compare a moving van with a stationary structure for this purpose. Just try putting a mis-sealed double-pane window in your van for awhile and see what happens. If the vehicle spends time in a locale where there is any appreciable humidity, the problem will occur.

I had a career in managing the designs of buildings as the Prototype developer and in new buildings in different climates and most of the United States. You most certainly do design walls differently in Minneapolis as opposed to Miami. So a van has to be a compromise. I mentioned the 100% Hushmat is probably the key to condensation prevention on the inner skin of the metal wall. The insulation thickness does not prevent moisture reaching the inner metal skin. So, keeping out as much moisture as possible is the key. The sun beating down on metal skin will radiate drying out insulation better than most any building.

Yes the rule of thumb in buildings is not to have two vapor barriers, but vans are not buildings and usually don't have weep holes in walls and generally are not less than 2" thick with metal skins. You are over expressing building technology that doesn't apply to vans. BTW, we did not place any vapor barrier in our Miami buildings since you want to have vapor pass through completely to the outside and there is little chance of it condensing.

I didn't touch much on spray foams. You mentioned extruded polystyrene as a true impermeable vapor barrier. That's true, I built my timber frame house with 5-1/2" thickness with it with building sheathing like a sandwich panel. I wrapped my house inside with exposed to the inside 2" in T&G pine boards.. Extruded polystyrene boards could be used in a van with no harm but it is probably not any more efficient than the other insulations and can't be installed in those nooks and krannies very easily.

Sprav foams such as polyisocyanurate are impermeable as well but they have some practical installation problems but no harm as far as vapor that I can see. I caution that I had a rule as I tested every spray foam on the market and had them analyzed by a laboratory that there was a lot of sham products on the market. I came up with a rule, if the spray foam was white it was a no go. They all proved they soaked in water like a sponge and then didn't give it up. I don't know if there are new products since 13 years ago but there was a not of bogus information and claims. Polyiso's are khaki colored.

[Bud]

George, this is extremely political, so I'll let avanti deal with it:

"physics by feelings are still rampant"

Bud

[avanti]

Originally Posted by Bud

George, this is extremely political, so I'll let avanti deal with it:

"physics by feelings are still rampant"

Bud

Here's more politics:

"Facts first"


Please don't add vapor barriers to your van.

[Bud]

Originally Posted by avanti

Here's more politics:

"Facts first"


Please don't add vapor barriers to your van.

avanti, please understand, I'm sorry. I should have considered the circumstances - the specific posts and thoughts, facts, opinions, etc.

I was only referring to George's words, But Unfortunately without some dots....... took them out of context. Dumb on my part.

Your points were not lost on me or others, and thanks.

Bud

[GeorgeRa]

Originally Posted by Bud

George, this is extremely political, so I'll let avanti deal with it:

"physics by feelings are still rampant"

Bud

It was not my intent to be political, good engineering is based on physics.

[Davydd]

This video is a follow up of ARV's "What we know (and don't know) about van insulation." They answer why they don't use spray on insulation and mineral wool. And they added discussion of reflective window tint which they do use.

https://www.youtube.com/watch?v=diFO...gVZ45-7nq7Y5Yw