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Old 08-19-2022, 11:07 PM   #1
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Ecofoil for ceiling

My dad recommended installing this under the insulation for my ceiling, since I live in southwest Florida. So how would I apply it?? And is this truly a good idea or totally unnecessary?


From website:

"What is the benefit to adding EcoFoil reflective insulation to a metal building?

Insulation provides increased comfort, energy savings, condensation control and light reflectivity."
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Old 08-19-2022, 11:50 PM   #2
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That stuff is handy for sewing into shades and curtains, for blocking windows, but it's almost useless when sandwiched into a wall without any air gaps on both sides. Personally, I wouldn't waste my money on that. I'm no insulationologist, but there are some pretty knowledgable folks here who can provide more technical input.
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Old 08-20-2022, 11:02 AM   #3
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Ditto Ross.

The method by which reflective 'insulation' works is by reflecting radiant heat. But this type of thermal transfer is but one of many, and essentially irrelevant in most cases where convection & conduction will generally end up short-circuiting any benefit you may have created, assuming it was installed in a manner in which any benefit could be had, which most people dont. It can be useful in some specific circumstances, as part of - not a replacement for - an insulation envelope. But in most cases, the space required for the requisite air gap will yield better performance filled by an actual insulative material.

None of these shiny sheets are good insulation. The insulative performance of any material is a function of it's resistance to heat transfer, and its thickness. That's all insulation does... Slow heat transfer from one side of it to the other. These are neither thick enough, nor insulative enough, to do anything. Literally money down the drain.

About the only thing its good for in a bus is keeping sun out of the windows, and even then without an air gap between the foil & glass you're giving up a big part of the benefit.
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Old 08-20-2022, 01:53 PM   #4
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Yep not worth it.
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Old 08-20-2022, 03:09 PM   #5
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Thanks everyone!!!
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Old 08-20-2022, 05:20 PM   #6
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To add a little "insulationology" to this, there are basically three methods of heat transfer in our universe (there's also a fourth, evaporative cooling, but that's not really relevant to anything except why people get colder when it's windy): conduction, convection, and radiation. Conduction occurs when atoms bump into other atoms and transfer their energy like pool balls running into each other on a billiards table. Convection occurs when a mass of material (either in gaseous or liquid form) moves and takes its heat energy with it.

Air (or any gas, really) transfers heat poorly via conduction because it is not very dense, but it transfers heat extremely well via convection (as does any gas or liquid). So for any kind of insulation to work effectively in a structure (like fiberglass, XPS foam, rock wool etc.) it has to trap lots and lots of tiny pockets of air in a physical matrix. Since insulation is composed of a large fraction of air or other gases, it conducts heat poorly, and since the tiny pockets of air are not free to move (much), it also convects heat poorly. The end result is a substance that heat moves through slowly, which is exactly what you want from insulation.

Heat transfer by radiation is different. Any substance above absolute zero temperature will occasionally emit photons of energy; the loss of this energy will cause the substance's temperature to gradually go down. This heat loss occurs without the material needing to come in contact with any other material and without the material needing to move anywhere (this is why it's so relevant in space, of course). The frequency of this photon emission (aka the rate at which heat is lost in this way) is a function of the material's absolute temperature taken to the fourth power.

This means that heat transfer via radiation increases rapidly as temperature increases, but it also means that heat transfer via radiation decreases rapidly as temperature decreases. It just so happens that at the temperatures humans typically live in (say, 100°F and below) the amount of heat transferred via radiation is nearly nothing when compared to the amount transferred via conduction and convection. When you get into the temperatures of a material heated above the ambient air temperature by direct sunlight (say, 140°F on the roof of a school bus or 165°F on the black asphalt roof of a house) you start to get a significant (but still pretty small) amount of heat transferred by radiation. When you start talking about the temperatures of a wood stove (maybe 400°F to 500°F) then the amount of heat transferred by radiation becomes more significant than that via conduction and convection (hence the need for a radiative heat shield with a wood stove, something not everybody in the skoolie world seems to actually install).

Long story short: bubble-and-foil reflectix-type insulation is pretty much worthless because a) the bubbles are too big to block heat transfer via convection and the overall material is too thin to have any real effect on conduction, and b) the foil is useless against radiative heat transfer because there's nearly none of that happening (except in the special case of sunlight coming through the windows, and aluminum foil would do the same job only a lot cheaper).

The insulation also leads to a special logical problem sometimes. In a house, reflective insulation can be used to somewhat block the radiative heat coming off the hot roof into the house. If the foil layer is installed in the attic with the foil facing upwards (and if the air in the attic is free to circulate to the outside), then it does provide a small cooling effect, usually given the equivalent R-rating ("equivalent" because R-rating is literally the inverse of thermal conductivity, something that does not really apply at all to radiative heat transfer) of 2.5. Since reflectix-type insulation is usually 1/4" thick, some people imagine that multiple layers of reflectix will provide a superb R-value of 10 per inch - definitely not the case.
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Old 08-21-2022, 10:15 AM   #7
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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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Old 08-21-2022, 07:01 PM   #8
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R-10/inch, Ha

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Originally Posted by musigenesis View Post
If the foil layer is installed in the attic with the foil facing upwards (and if the air in the attic is free to circulate to the outside), then it does provide a small cooling effect, usually given the equivalent R-rating ("equivalent" because R-rating is literally the inverse of thermal conductivity, something that does not really apply at all to radiative heat transfer) of 2.5. Since reflectix-type insulation is usually 1/4" thick, some people imagine that multiple layers of reflectix will provide a superb R-value of 10 per inch - definitely not the case.
That has been my experience, as well, MG. I have found no evidence of such wild claims. We bought two kits of FrothPak650 as I never found a reliable product over 6.5 per inch. Even with the spray foam, tests show that R values drop over time, months then years. R-10 / inch is a dreamer's fantasy. Snake oil salesmen prey on hope & faith.
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Old 08-21-2022, 10:12 PM   #9
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Quote:
Originally Posted by musigenesis View Post
Heat transfer by radiation is different. Any substance above absolute zero temperature will occasionally emit photons of energy; the loss of this energy will cause the substance's temperature to gradually go down. This heat loss occurs without the material needing to come in contact with any other material and without the material needing to move anywhere (this is why it's so relevant in space, of course). The frequency of this photon emission (aka the rate at which heat is lost in this way) is a function of the material's absolute temperature taken to the fourth power.

I have to wonder, what are you doing to seal edges and maintain a radiative gap between layer? And seal edges, trapping air?
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Old 08-21-2022, 10:27 PM   #10
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Originally Posted by TaliaDPerkins View Post
I have to wonder, what are you doing to seal edges and maintain a radiative gap between layer? And seal edges, trapping air?
Well, nothing yet, I haven't made it that far. I'm just gathering preliminary information..isn't spray foam used to fill the gaps??
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Old 08-22-2022, 05:27 AM   #11
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I have to wonder, what are you doing to seal edges and maintain a radiative gap between layer? And seal edges, trapping air?
I'm not sure if you actually read my post here re: insulationology. My bus' insulation is not built to deal with radiative heat transfer because there is effectively no radiative heat transfer happening at normal temperatures of around 100°F or lower (conduction and convection are the big concerns). My insulation has no foil layer so there would be no purpose to an air gap anywhere anyway. The only situation in which radiative heat transfer would be relevant is when my bus is out in direct sunlight which heats the roof well above the ambient air temperature; for this my roof is painted white and I plan to park in the shade, artificial or otherwise. Even in direct sunlight when my bus roof gets to 135°F or 140°F, my ceiling inside only measures a few degrees above the ambient air temperature anyway, thanks to the 2.25" of XPS and the thermal isolation of the ribs.

My XPS panels were cut slightly large for their spaces and hammered into place, so the air seal is good - certainly not as good as that provided by well-done spray foam, but adequate for the purpose.
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Old 08-22-2022, 06:29 AM   #12
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Radiation is not the only thing MLI blocks. Installed with sealed edges it also prevent convection and is a very poor thermal bridge, also blocking conduction. Even the Reflectix foil bubble wrap is not terrible, and many layers can be fit into a shallow depth. It is chiefly the pain-in-the-buttness of installing so it can be effective that I will not consider it.



Please understand I am an advocate for closed cell spray foam -- but lots of people use layers of Reflectix successfully. It is not any scam.
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Old 08-22-2022, 07:01 AM   #13
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Radiation is not the only thing MLI blocks. Installed with sealed edges it also prevent convection and is a very poor thermal bridge, also blocking conduction. Even the Reflectix foil bubble wrap is not terrible, and many layers can be fit into a shallow depth.
There is literally no substance in the universe that "blocks" conduction (a vacuum blocks conduction but a vacuum is not a substance). All materials have a thermal conductivity, which indicates the ease with which heat energy travels through it. Reflectix has a high overall thermal conductivity (and hence a low real R-value) because its large-scale bubbles allow heat transfer via convection, something air is very good at. Its alleged R-value of 3 for a 1/4" layer is fictional and is based almost entirely on the assumed benefit of the foil layer reflecting radiant heat (which, as I mentioned, is nearly nonexistent in normal conditions).

Even in a situation where Reflectix is providing an effective radiant barrier with a functioning externally-vented air gap, you do not gain any benefit from having multiple reflective layers sandwiched together. Reflectix is terrible and multiple layers of terrible insulation do not make good insulation, at least not anything close to what proper insulation of the same thickness will provide. 2" of XPS foam board will give R-10 and 2" of spray foam will give R-13 (at least in temperatures of 75°F and above); the idea that 2" of layered Reflectix will give R-20 (as you stated in an earlier post on this thread) is a strange fantasy.
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Old 08-22-2022, 07:12 AM   #14
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Quote:
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There is literally no substance in the universe that "blocks" conduction (a vacuum blocks conduction but a vacuum is not a substance). All materials have a thermal conductivity, which indicates the ease with which heat energy travels through it. Reflectix has a high overall thermal conductivity (and hence a low real R-value) because its large-scale bubbles allow heat transfer via convection, something air is very good at. Its alleged R-value of 3 for a 1/4" layer is fictional and is based entirely on the assumed benefit of the foil layer reflecting radiant heat (which, as I mentioned, is nearly nonexistent in normal conditions).

Even in a situation where Reflectix is providing an effective radiant barrier with a functioning externally-vented air gap, you do not gain any benefit from having multiple reflective layers sandwiched together. Reflectix is terrible and multiple layers of terrible insulation do not make good insulation, at least not anything close to what proper insulation of the same thickness will provide. 2" of XPS foam board will give R-10 and 2" of spray foam will give R-13 (at least in temperatures of 75°F and above); the idea that 2" of layered Reflectix will give R-20 (as you stated in an earlier post on this thread) is a strange fantasy.

Vacuum blocks conduction. Completely. The closer a volume is to a vacuum, the more conduction is blocked. That is all your XPS or the spray foam I prefer are doing -- making a very long (if stretched out straight) path through a poor conductor, which poor conductor is trapping a lot of air so conduction and convection are minimized.


Claiming the bubbles are too large for Reflectix to have an R value is silly. especially when it is multiple layers of it being considered, and even fiberglass batt has insulative value even thought it has no continuous membrane barring air infiltration (unless it has a non-perforated backing and is taped at the edges, or is accompanied by some other membrane.


Yes, you gain every time a layer is added -- that is how MLI works. It is not great at near room temps, but even a continuous sheet of any membrane will block infiltration. Filling the volume with something air can't circulate through prevents convection from being much of a loss mechanism. If the volume isn't filled with a solid, then conduction will be poor.


"the idea that 2" of layered Reflectix will give R-20 (as you stated in an earlier post on this thread) is a strange fantasy." <-- Go ahead and try it. You fill an envelop around a volume with trapped air in tiny spaces, it will tend to trap heat (in or out).
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Old 08-22-2022, 08:08 AM   #15
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Attic Space

Quote:
Originally Posted by Wildfloweramanda View Post
My dad recommended installing this under the insulation for my ceiling, since I live in southwest Florida. So how would I apply it?? And is this truly a good idea or totally unnecessary?
-----------------------------
Musigenesis is typically 99% accurate. The rest of us skoolie & van life folks have a history of mixing facts, still most appear to agree with MG's assessment. Please consider reading more about radiant barriers, from the insulation professionals, here:
www.atticconstruction.com/most-common-radiant-barrier-problems/

Radiant barriers only work properly in an attic that’s ventilated properly.

Proper attic ventilation ensures that reflected heat circulates.

Without proper ventilation, a thermos effect will be created, and the radiant barrier can produce the opposite of its intended effect, increasing the temperature in your attic space.

In order for the reflected heat to dissipate, there needs to be air circulation that carries hot air around instead of letting it sit still. That still air is also a main factor in Dust buildup.

*Dust is also the absolute biggest threat to your radiant barrier.
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Old 08-22-2022, 03:23 PM   #16
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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.
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Old 08-23-2022, 07:28 PM   #17
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Here's a discussion and a wealth of info from building professionals (engineers) on the subject. Specific to reflectix, but applicable to all the magic shiny sheets...


https://www.greenbuildingadvisor.com...-guy-is-hooked
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Old 08-23-2022, 07:34 PM   #18
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Ditto Ross.

The method by which reflective 'insulation' works is by reflecting radiant heat. But this type of thermal transfer is but one of many, and essentially irrelevant in most cases where convection & conduction will generally end up short-circuiting any benefit you may have created, assuming it was installed in a manner in which any benefit could be had, which most people dont. It can be useful in some specific circumstances, as part of - not a replacement for - an insulation envelope. But in most cases, the space required for the requisite air gap will yield better performance filled by an actual insulative material.

None of these shiny sheets are good insulation. The insulative performance of any material is a function of it's resistance to heat transfer, and its thickness. That's all insulation does... Slow heat transfer from one side of it to the other. These are neither thick enough, nor insulative enough, to do anything. Literally money down the drain.

About the only thing its good for in a bus is keeping sun out of the windows, and even then without an air gap between the foil & glass you're giving up a big part of the benefit.

inside a wall you are right. useless.. i use this type of stuff most effectively on engine compartment firewalls, engine side of engine dog-houses, I also put it on the bottom of my floor above and around the transmission.. essentially reflecting engine heat and near-engine heat out.. there is easily a 20 degree difference in my floor and inside firewall temperatures vs just the original rubber.. it does exactly as you say.. reflects back the Radiant heat!
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Old 08-23-2022, 07:45 PM   #19
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Exactly, Christopher. Reflectix-like products are great in that application. Same for reducing heat coming in from windows so long as you maintain a decent air gap between it & the glass / frame.

I really need to do exactly what you've done (list just grew again, lol). We have some factory applied reflective insulation, but not enough.
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Old 08-23-2022, 08:04 PM   #20
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Exactly, Christopher. Reflectix-like products are great in that application. Same for reducing heat coming in from windows so long as you maintain a decent air gap between it & the glass / frame.

I really need to do exactly what you've done (list just grew again, lol). We have some factory applied reflective insulation, but not enough.

I did it because i run road A/C.. and often seem to end up in texas / florida / alabama etc in july / august which taxes any bus A/C system to the max.. I like my bright light and visibilty so i refuse to tint the windows or cover them uo while driving.. so keeping every other bit of heat out is paramount to me staying nice N cool in 100 degree humid heat...
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