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Discussion Starter · #1 ·
I've been reading / watching / etc. a bunch on building up a van, and one thing I've been trying to sort out is the thermal breaks and the interior walls - specifically on how to insulate in front of the wide ribs on the side / rear. I've filled them with Havlock wool, but there is still the problem of "I have a big chunk of metal close to / exposed in the living area. However, it struck me that in my van, all of the panels / etc. appear to be glued / epoxied on. Should this glue / epoxy act as a thermal barrier, and effectively stop the heat/cold from the exterior from conducting to the interior?
 

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You should probably Search first before asking, Thermal Breaks have been pretty well covered in this forum thread.

 

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Hi,
You can insulate the thermal breaks -- here is a study using an IR camera to look at a couple methods...

This is all in a ProMaster van, but probably pretty much the same story as the Transit.

Some people have the impression that thermal bridging is a huge heat loss for the van, but its not to awful -- about 25% of the van heat loss for a well insulated van. I'd say the priorities are walls/ceiling/floor, then windows, then thermal breaks.

Gary
 

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Again, 25% of the heat loss can occur through uninsulated ribs. The thermal bridging only accounts for about 10% of the total heat loss through the ribs. So in your example, 2.5% of the heat is lost through the thermal bridge, and the other 22.5% is lost through the uninsulated inner ribs space.

This whole rib insulation issue has been mischaracterized. Again, I realize that people do not care, but insulating the interior of the ribs will have a wildly larger impact when compared to a 1/4" piece of insulation over the face of the rib.
 

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In my many years of helping folks with van builds and advising and selling insulation it not uncommon to see some folks experience analysis paralysis. It's a van and will never be as thermally efficient as a stationary structure and doesn't need to be. It's a small space and with a decent heater it won't be hard to stay comfortable in cold weather. It it is hot out and the van is not air conditioned then find some shade and sit outside.

There are some areas where thermal bridging can be a problem. If you have a ceiling panel that is attached directly to the metal roof beams and you are sleeping directly underneath in an elevated bed then condensation can form and drip on you. So placing a thermal break between the ceiling panel and the beams is a good idea. If using a tongue and groove ceiling then a furring strip (we like expanded PVC) attached to the roof beam will provide the thermal break and also make installing the boards easier.. A layer of Low-E (also sold a EZcool) on the back of the ceiling panel is also effective. Another place where a thermal break is desired is when attaching metal framing like 8020 to the van structure. Cold enegry can soak into the aluminum and make it cold to the touch. Again a block of expanded PVC is a good solution.

All the best,
Hein
DIYvan
 

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Again, 25% of the heat loss can occur through uninsulated ribs. The thermal bridging only accounts for about 10% of the total heat loss through the ribs. So in your example, 2.5% of the heat is lost through the thermal bridge, and the other 22.5% is lost through the uninsulated inner ribs space.

This whole rib insulation issue has been mischaracterized. Again, I realize that people do not care, but insulating the interior of the ribs will have a wildly larger impact when compared to a 1/4" piece of insulation over the face of the rib.
I guess I do not understand your logic.

The test with the IR camera uses the temperature of the inner surface of the wall at the rib to compare heat loss for the two methods of insulating for thermal breaks. In the end its only the temperature of the inside surface of the wall that determines the heat transfer into the van space, so the effectiveness of the thermal bridge insulation method is proportional to the amount it lowers the inside surface temperature.

Again, not really an issue for the most people use their vans in three seasons, but significant for winter users.

Gary
 

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Insulate right over them and go with a soft easy to clean upholstery wall and roof material (lightweight and no rattles, squeaks, or planks to fall off).

That's my plan anyways. I also took photos of the ribs and occasionally use a needle to find existing holes when I want to create a location for a wood+minicell furring strip. It sure seems logical to me, but everyone has their method and mine isn't perfect either. Just do the best you can and don't kill yourself trying to insulate a lost-cause metal structure.

Heat is cheap and easy to add. Cooling is very hard, especially if it's efficient and needs to last for many days at a time (e.g. high SEER minisplit with massive lithium bank). If you go the a/c route, then thorough floor insulation is also important since cold air falls, and I can tell you from experience the metal floor of the van gets really hot in places like AZ.

Good luck. More about my methods (ongoing) in the link in my signature.

Here's an example of my wall and roof layer 1 (SM 600L), to be followed by true foil faced ez-cool reflective barrier, then upholstery finish. I may also add some additional rigid foam board to the roof after I get the minisplit installed and compare my real world power requirements with my current estimates.

And then an example of the floor sandwich (minicell, 3M TAI, 1" XPS, birchwood, vinyl).

Cheers.

143984


Clicked the wrong photo but man that was a good day parasailing. Can't wait to get back to Mexico after this covid madness wraps up.
143985


There we go...
143986
 

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So there are two different concepts at work here. A thermal bridge is a continuous span of consistent material (often high conductivity) between two surfaces. In this case, the side walls that are perpendicular to the van wall are the thermal bridge. The metal facing the interior is not itself a thermal bridge, but does act as a conductive path between the thermal bridges, the pillar interior, and the inside of the room. The insulation inside the C-pillar has no affect on the thermal bridge.

So there are two factors at work, conduction and convection (and to a lesser extend radiation inside the pillar). The thinsulate used inside the pillar affects how heat moves through the interior of the pillar but has no affect at all on the thermal bridge. The foam on the outside of the pillar has no affect on the interior conduction and convection, but does provide a thermal break in that it adds insulation that inhibits heat transfer from BOTH the thermal bridge and the pillar interior.

The result of the study is predictable. A 5.2 R value (Thinsulate seems to be a good product, but this number seems to be up for debate, and R-value is a sketchy metric from a scientific perspective), is not high at all. The 1/4" insulation (be it foam, plywood or anything really) is going to be very close to R-1. The reason you see the better temperature outputs on the study are two fold. First, the foam thermal break is affecting both the thermal bridge and the pillar interior. Second, the Thinsulate is likely not evenly distributed within the column and it therefore very unlikely providing an equivalent r-5.2 value. It is conjecture, but I would wager that the effective R-value of Thinsulate installed that way is likely 3 or less. If you are really interested in the effectiveness of insulation installation techniques, home building publications love this kind of thing.

In the end, the R-value of the Thinsulate and the foam are likely within an order of magnitude of each other and the foam is addressing the thermal break in addition to the pillar interior. This is the reason the the results of the study show the foam being more effective. The same study done with a true loose fill or foam that actually filled the column would provide different results. The real comparison test would be: 1) empty pillar, 2) thermal break only, 3) insulated pillar only, 4) insulated pillar with thermal break. This study would address the two different issues that seem to always come up in these threads.

For my van, I insulated my ribs and pillars best I could with spray foam, and areas where I might need future access I tore rock wool into tiny pieces and loose filled. I did not use a thermal break other than the plywood screwed to the walls (again, this will give about R-1). The thermal break of additional foam is certainly valuable, but for my build I am using the wall material for lateral and torsional strength and wanted the plywood directly connected to the ribs and pillars.
 

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This whole rib insulation issue has been mischaracterized. Again, I realize that people do not care, but insulating the interior of the ribs will have a wildly larger impact when compared to a 1/4" piece of insulation over the face of the rib.
I strongly disagree, as does the math and physics. The rib is essentially two small resistors (metal sides) and a large resistor (filled interior) in parallel, all in series with a very small resistor (metal rib face). The metal parallel paths dominate.
 

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I strongly disagree, as does the math and physics. The rib is essentially two small resistors (metal sides) and a large resistor (filled interior) in parallel, all in series with a very small resistor (metal rib face). The metal parallel paths dominate.
I am not sure what part you disagree with. Here is all the math and a pretty picture. The metal thermal bridge has a tiny cross sectional area, and therefore just can't move that much heat, even though it is made of a highly conductive material.
 

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Again, 25% of the heat loss can occur through uninsulated ribs. The thermal bridging only accounts for about 10% of the total heat loss through the ribs. So in your example, 2.5% of the heat is lost through the thermal bridge, and the other 22.5% is lost through the uninsulated inner ribs space.

This whole rib insulation issue has been mischaracterized. Again, I realize that people do not care, but insulating the interior of the ribs will have a wildly larger impact when compared to a 1/4" piece of insulation over the face of the rib.
It's eye opening, because the ribs are far less than 25% of the surface area. Perhaps the mass of the ribs when flattened are equivalent to 25% of the roof surface area. Conduction is a lessor heat exchange than convection, but more than radiation. Convection would be limited to almost zero in an uninsulated rib, and there is the variable of the SIDES of the rib being insulated by the insulation on either side filling the space between ribs, leaving just the surface area of the exposed roof inside uninsulated, and the conduction of the side of the rib itself. Conduction must be a multiplier for the surface area temps, by mass.

Not questioning the numbers, just trying to figure out why they are so disproportionately high.
 

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So there are two different concepts at work here. A thermal bridge is a continuous span of consistent material (often high conductivity) between two surfaces. In this case, the side walls that are perpendicular to the van wall are the thermal bridge. The metal facing the interior is not itself a thermal bridge, but does act as a conductive path between the thermal bridges, the pillar interior, and the inside of the room. The insulation inside the C-pillar has no affect on the thermal bridge.

So there are two factors at work, conduction and convection (and to a lesser extend radiation inside the pillar). The thinsulate used inside the pillar affects how heat moves through the interior of the pillar but has no affect at all on the thermal bridge. The foam on the outside of the pillar has no affect on the interior conduction and convection, but does provide a thermal break in that it adds insulation that inhibits heat transfer from BOTH the thermal bridge and the pillar interior.

The result of the study is predictable. A 5.2 R value (Thinsulate seems to be a good product, but this number seems to be up for debate, and R-value is a sketchy metric from a scientific perspective), is not high at all. The 1/4" insulation (be it foam, plywood or anything really) is going to be very close to R-1. The reason you see the better temperature outputs on the study are two fold. First, the foam thermal break is affecting both the thermal bridge and the pillar interior. Second, the Thinsulate is likely not evenly distributed within the column and it therefore very unlikely providing an equivalent r-5.2 value. It is conjecture, but I would wager that the effective R-value of Thinsulate installed that way is likely 3 or less. If you are really interested in the effectiveness of insulation installation techniques, home building publications love this kind of thing.

In the end, the R-value of the Thinsulate and the foam are likely within an order of magnitude of each other and the foam is addressing the thermal break in addition to the pillar interior. This is the reason the the results of the study show the foam being more effective. The same study done with a true loose fill or foam that actually filled the column would provide different results. The real comparison test would be: 1) empty pillar, 2) thermal break only, 3) insulated pillar only, 4) insulated pillar with thermal break. This study would address the two different issues that seem to always come up in these threads.

For my van, I insulated my ribs and pillars best I could with spray foam, and areas where I might need future access I tore rock wool into tiny pieces and loose filled. I did not use a thermal break other than the plywood screwed to the walls (again, this will give about R-1). The thermal break of additional foam is certainly valuable, but for my build I am using the wall material for lateral and torsional strength and wanted the plywood directly connected to the ribs and pillars.
Hi,
Don't really disagree with your thoughts on this much, but...

My recollection is that the Thinsulate did really fill the cavities pretty well -- not sure you could do much better with a true loose fill.

I mentioned that the sill seal foam tape that I used for thermal break insulation on the inside surface of the ribs is not an optimal choice -- it was just what I had on hand. One could probably do better with different materials without adding much thickness.
For example, half inch Polyiso would give R3+.

I did have a go at measuring the convective airflow velocity through the rib channel with the very sensitive Dwyer meter and did not get very high velocities at all (15 fpm (0.17 MPH) with rib bay empty). Maybe this is some indication that convective heat transfer inside the rib is not that large (compared to the conduction through rib webs).

In the end, for most people's van use, the thermal bridging is not much of an issue, and not worth worrying about.

Gary
 

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I think that we can assume the cavities are sealed for the most part. I did in the calcs anyway, giving it the benefit of the doubt. So the only convection you have if from natural air flow within the cavity.

Your study was awesome by the way. I just feel like this whole conversation would be better if people had a better grasp of how the heat transfer actually works.
 

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Discussion Starter · #20 ·
Thanks for all the discussion so far.

You should probably Search first before asking, Thermal Breaks have been pretty well covered in this forum thread.

Yeah - I found that post a while after posting this one. I've been lurking on and off for a few months while waiting for my van to actually arrive (it now has). It was a very enthusiastic discussion for sure.

I probably should have added a bit more background to my original query. One thing I am planning on doing is building with 8020 or some other extruded aluminium. I saw some posts where a whole craptop of effort was put into crafting custom components to break the 8020 length from the bolt that attaches it to the wall / bracket / etc. But then wondered how important that actually was, given the foam material that seems to be quite prevalent. It hasn't really gotten cold enough in the PNW to do any real-world testing.
 
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