Ecofoil for ceiling

[LargeMargeInBaja]

Intention?
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I think keeping the sun away from the metal roof makes sense, compared to dealing with a hot metal ceiling.

[Veloc]

If you want R10 per inch you're going to be looking at something like Aerogel, which has an R value of 9.6/inch. But, you're going to pay through the nose for it. That stuff ain't cheap. And, no idea how it performs over time. NASA developed it for spacecraft insulation, and these people have been using the tech to develop insulation for the little people with a lot of money.

https://www.aerogel.com/product/spaceloft/

[TaliaDPerkins]

Please bear in mind I have never advocated for the use of Reflectix type insulation in terrestrial vehicles, I think closed cell spray foam is a far, far better way to get the job done.


However, the criticisms I have seen made of metalized bubble wrap are not based in physics at all.


The air gap and ventilation requirement are an artifact of the plastic substrate needing to be kept below a certain temperature so it's mechanical characteristics are not degraded by heat on the hot side. Every other layer is cooler and can be spaced from any other layer by just 0.1mm and work fine. They "stack" just fine.


I have ordered 10 temp sensor probes, Pt100 RTD's. I can borrow a set of gear from work which can easily record 16 of these at +/- 0.1degC, I plan on using at least 4 of the probes.


Under a plexiglas cover admitting sunlight, all enclosed in a frame producing the required air gap and providing ventilation for that first layer, I will stack the following from out side to "inside":


plexiglas, air gap, probe, 12"x12" steel sheet (probably 24ga since I can get that easy), probe, 2" deep stack of metallized bubble wrap spaced as minimally as I can arrange for, probe, another metal sheet, and a probe.


Edges of all layers to be taped in such a way convection through the edges of the stack does not occur. I will likely use foam plastic to space the layers, but as that at the edges of the bubble wrap stack will be an inch or two from the edges of the metal sheets, they will not meaningfully bridge to the metal.


The conductivity of steel is well published, and the area is like 144" square.


How much heat is exiting the bottom surface as the top is exposed to the sun and how much is going into/through the top metal is easily calculable, and given the parallelism in construction it should be a representative measure of the effectiveness of such a depth of Reflectix.


Chief likely point of failure I can see is, that first metal layer gets so hot the Reflectix fails. That happens I go back to the drawing board.

[TaliaDPerkins]

Originally Posted by TheHubbardBus

There simply is no way reflectix or similar materials achieve R10 / inch by stacking layers. Show me one legitimate citation, @TaliaDPerkins, where its used in-wall, and not reliant on an air gap.

I never claimed* you could get R10 in an inch by stacking bubble wrap, but R7 seem quite doable (with 1/8 thick bubble wrap). It's just so much effort I think spray foam is better.


*Unless I typoed something

[DeMac]

Originally Posted by TaliaDPerkins

For overall easy of installation, permanence, high performance -- closed cell spray foam. Yes it has a lot of prep work, but it is very durable, low maintenance and adds quieting as well as superlative sealing of the structure against air infiltration where it is present.


Radiative barriers work fine at both preventing radiative transfer and if installed with care prevent air infiltration and convection as well (you have to seal/tape up all edges). I think it might actually take more time to for example take 1/2 wood strips bordering all spaces to be sequentially laid up in layers with reflective bubble wrap style insulation to get 4 layers, and then it would have an effective R value in excess of 20 in 2 inches thickness. Three inches of spray foam gets you there I think with far less trouble. And those strips laid up make a bit of a thermal bridge. Also have to find a tape that is 100% good for a decade or two at in the sun and freezing cold temps (how soon do you want your bus to need stripped or junked?).

.
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....an effective R value in excess of 20 in 2 inches thickness......
post #7
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We read this statement, written by someone with access to your account. Not actually the specific English words used to convey the message. But, yeah.

(Nice example of modern journalism)

[TaliaDPerkins]

At that, if I could find some 1/20th inch thick bubble wrap, I suspect R10/inch could be done*. What I had in mind there was bubble wrap equalling close cell foam per inch, and was thinking of my 3" application of that spray foam with approx. R20. My apologies for my error.


*I don't think it would be worth doing.

[TheHubbardBus]

Originally Posted by TaliaDPerkins

Please bear in mind I have never advocated for the use of Reflectix type insulation in terrestrial vehicles, I think closed cell spray foam is a far, far better way to get the job done.


However, the criticisms I have seen made of metalized bubble wrap are not based in physics at all.


The air gap and ventilation requirement are an artifact of the plastic substrate needing to be kept below a certain temperature so it's mechanical characteristics are not degraded by heat on the hot side. Every other layer is cooler and can be spaced from any other layer by just 0.1mm and work fine. They "stack" just fine.


I have ordered 10 temp sensor probes, Pt100 RTD's. I can borrow a set of gear from work which can easily record 16 of these at +/- 0.1degC, I plan on using at least 4 of the probes.


Under a plexiglas cover admitting sunlight, all enclosed in a frame producing the required air gap and providing ventilation for that first layer, I will stack the following from out side to "inside":


plexiglas, air gap, probe, 12"x12" steel sheet (probably 24ga since I can get that easy), probe, 2" deep stack of metallized bubble wrap spaced as minimally as I can arrange for, probe, another metal sheet, and a probe.


Edges of all layers to be taped in such a way convection through the edges of the stack does not occur. I will likely use foam plastic to space the layers, but as that at the edges of the bubble wrap stack will be an inch or two from the edges of the metal sheets, they will not meaningfully bridge to the metal.


The conductivity of steel is well published, and the area is like 144" square.


How much heat is exiting the bottom surface as the top is exposed to the sun and how much is going into/through the top metal is easily calculable, and given the parallelism in construction it should be a representative measure of the effectiveness of such a depth of Reflectix.


Chief likely point of failure I can see is, that first metal layer gets so hot the Reflectix fails. That happens I go back to the drawing board.

I don't really understand where you're going here.
Did you read the info at the link I provided?
There are standardized tests to measure material r-value. These standardized tests prove reflectix to have a material rvalue of 1.08 for its 5/16" of thickness. About 4 per inch.
Their advertised r value of 6 assumes a 3/4" air gap, when used in the very specific case of HVAC ducting. It is an assembly rvalue. It has nothing to do with heating of the material, as the material itself is almost irrelevant. It can't be used to compare to other products, as others products don't use assembly rvalues in an attempt at deception.
And yes, you did say 10/inch, as already pointed out (if its 20 for 2", isn't it 10 for 1"?).
Now you're saying 7. Based on what, exactly? Feelings? Why the 3 point drop?
If I'm comparing products, I'm going to use the same standardized test on all of them.
Just about everything but fiberglass batt beats 4/inch. And if you want ~6, you can get that with polyiso, among other things, without going through the hassle of attempting to construct and maintain that air gap that in most cases only works well in one direction.