Aluminium foil insulation vs styrofoam
Hi All. I am a newbie to this forum . I am building a concrete house in Belize Central America with a vaulted wood ceiling. I need to insulate the roof to keep out the HEAT!!!. I was going to insulate with a 2″ blue board type of styrofoam, but that would only give me an R -10. I have been doing reasearch on the internet and have come across a product called PRODEX total insulation, which is a 1/4″- foil,foam,foil product with what they say is a R-14 rating. Have any of you used it? If so would you use it again? Does it really have that high of an R rating? Does anyone regulate claims of R ratings? I was thinking of applying it in the following way; – Rafter (on 2’center) -1×4″ decking -2×4″ sleeper (on top of rafter)with 1″ blueboard in between -Prodex as vapor barrier and extra insulation -1×4″ strapping -metal roofing
That would give me about a 1/2 ” space between blueboard and foil and the requsite 3/4″ space between foil and roofing and give me an R rating of 19. Is there a better way? Am I asking too many ?s like I said I am new. Thanks Carpenterdancingirl
Replies
Carpenter Dancing Girl,
You asked, "Does it (Prodex) really have that high of an R rating?" The answer is simple: No. Prodex distributors are lying. They are also violating federal law. I am in the process of reporting these Prodex illegal marketing schemes to the Federal Trade Commission. The federal R-Value Rule prohibits R-value exaggerations like these.
Wow I guess I hit a nerve. Have you used it yourself with bad results?
C.D.G.,
I haven't used it, but I am quite familiar with the exaggerations of companies promoting foil/bubble pack products and foil/thin foam/bubble pack products. I've written a few articles on the subject. I'm seen friends and neighbors misled by manufacturers' reps of some similar products, and seen them waste money on low-R products. To me, exaggerated R-value claims amounts to fraud -- materials suppliers and taking money from victims' pockets by making unfounded claims. That's why I regularly notify the FTC of violations of the R-Value Rule.
I recognize the products limitations, but look at what is claimed in the site you linked - "# A radiant barrier insulation.
# Reflects 97% of radiant heat.
# Maximum R Value of 14.5 (varies with application)"since hers is a home in need of protection from RADIANT heat gain, it has some valueif installed correctly, it will reflect a tremendous amount of heat energy for herstating that it provides a MAXIMUM of 14.5 R-value is not the same as claiming full R-value. Some other makers say EQUIVALENT of....Of course it is necessary for consumers and professionals to be educated and learn to read between the lines to know what they are and are not saying there.But I think it falls short of fraud myself. If we apply that standard, I would have to say that the makers of FG batts are also guilty of fraud.
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"stating that it provides a MAXIMUM of 14.5 R-value is not the same as claiming full R-value. Some other makers say EQUIVALENT of...."The definition of R-value is the based on the flow of CONDUCTIVE HEAT. Since this is radiant heat barrier there can't be an R value.The best that they can do is to show a compelte assembly and defined the conditions and then show what a completel assembly with r-rated insulation under the same operatoring conditions would have to be for the same heat flow.But I agree. If this is a decent radiant barrier then it or similar would be usefull in this application.Florida Solar Institue has a number of studies and reports on radiant barriers in roof assemblies..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Is there a risk of bugs attacking the styrofoam?
Good question. Bugs do not eat foam, but they do often like to tunnel and make their homes in it. It is as friendly for them as it is for us.
Usually it is the ground crawling types though. I don't know how many fliers they have seeking homes with humans down there. Belize is a place that has always enchanted me and holds a place in my fantasies, but I really don't know all that much about it.If she can get borate treated that would be best.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I heard about the insects in Costa Rica chewing up all sorts of
man made materials (i.e. plastics etc.). I have no definitive
knowledge only anectdotal and, of course, what happened at a
forest campground in Costa Rica may not apply elsewhere.
Bugs, birds, squirrels, mice, and probably some other small rodents down there. All will dig into the stuff to nest, or just to be irritating.But all are discouraged by heat -- they'd be looking for somewhere moderately cool.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Good morning.
I am interested in hearing more about Belize - but have to run off the work now. more on that later. Hope you didn't suffer much from the recent hurricane.
The bubble foil stuff if you look closely does not claim R-14, but the equivalent of R-14, and that only in certain kinds of appliocations. Yours might almost be one of those.
To achieve the best out of it, you have to have is installed and suspended in a way that keeps 1" of free air space in from of it to benefit from the reflective properties. Normally one would also want to have the edges sealed tightly too.
But in your application, I think the best use would be to install similar to what you scope out, but making sure to leave space at top and bottom for ventilating. The combination of the foil wrap and foam is good, and both should be unharmed by your humidity.
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Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Piffin,
Plenty of Prodex distributors are falsely claiming that Prodex has an R-value of 14 or 14.5. Check out the Web site for Better Built Metal Sales (http://www.getbetterbuilt.com/prodex.htm) --“Prodex insulation is water-proof, sound-proof, Class A-1 Fire Rated and has an R-value of 14.5.”<!----><!----><!---->
Ain't that what I said?
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I hear that we didn't suffer any from the hurricane, but thanks for asking. Would you use the product if it was your house or would you just use the styrofoam, and if so is a vented roof so much of a concern with styrofoam?
My closest point of reference is two weeks I spend in Puerto Rico working on hurricane recovery there. Thinking of the construction of homes there, it seems to me that the stuff might work pretty well, installed more or less as you describe.I would be a little concerned about how the whole system would hold up in high winds, though.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
There are several overlapping issues you touch on in that one sentence.BTW, you sentence structure implies an active organized mind, well schooled, disciplined, and analytical - to me anyways.
;)If I had to use only one or the other, I would use the foam and still allow for ventilation above it, between it and the metal roof.
Typically, the ventilation is necessary to release moisture from within that works up through the roof package and would condense at the roof surface - backside - and falsely give sign that the roof is leaking. The colder the exterior temp is re the interior, the more pronounced this effect is.But in your case, I venture to guess, the primary reason for venting immediately beneath the roofing is to let airflow cool that surface, so the heat is not retained in the space where it then works to penetrate the home, to your discomfort.Think of a tent with rain fly, if you are familiar with that. The fly provides shade and air circulation to keep the interior more moderate with no insulation whatsoever.Because the foam is a far better insulation than the foil faced bubbles, that would be the first choice, aided by ventilation, and the foil could then add to the efficiency and overall effectiveness. The primary benefit of the foil is in reflecting radiant heat, but it has little value at all in preventing conductive, or convective heat loss.
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Thanks for the tent/ Fly analogy, that works for me. However that picture in a hurricane , not so good.
As stated, the product does not have that R value, but if installed with care could come fairly close in your situation. To achieve optimal effect it would need to be installed with air space on both sides, and preferably with ventillation of the space above it. If there's only an air space on one side you'd lose about 1/3 of the insulating effect. The optimal air space would probably be about two inches, but it would be effective down to maybe 1/2", especially if ventillated.
Go to ebay and insulation. I agree with the others on bubble mylar, but they also sell mylar film (reflective) pretty darn cheap. As noted,you need an air space betwixt foil and other surface. I have used the bubble stuff in impossible bathroom situations but other methods are more economical.
thanks I will check it out.