He keeps dragging out fiberglass punching bags in lousy construction methods (in the arctic example, completely inappropriate for the environment.) Building science has moved a long way from 1964 or 1976 or even 1987 (once there was DOE funding for chasing down the particulars.) The stuff is all now well characterized, and modeled performance has a high correlation with in-situ measured results.

Fact is, most of the shortcomings of fiberglass has more to do with lack of proper air-barriers (and vapor control) than the material itself. Some of the benefits attributed to radiant barriers in wall or ceiling assemblies have as much to do with it's functioning as an air barrier than any of it's reflectivity/emissivity properties. Air leaks into stud cavites with low density batting is both a thermal & moisture disaster in the making. In the 1980s conventional thinking was that putting 6mil poly as a vapor & air barrier on the "warm" side was going to cure all ills, but that mis-perception didn't last long amongst those actually studying the issue in detail. The lack of a top-side air-barrier on batting (or blown) low density fiber in attic installations guarantees that it doesn't perform to it's ASTM C 518 rated spec (the test plate itself forms air barriers both sides), and given the relatively low air-retardency of low-density goods it's surprising that it's allowed to be installed that way by code. It's as-installed performance in no way compares to it's test-sampled performance, when installed without an air barrier. But with air barriers both sides and no gaps/compressions allowing convection currents to flow un-impeded it isn't nearly as bad as "typical" installations. (By contrast 1.5lb cellulose is sufficiently air retardent that even without a topside air barrier it will perform close to it's ASTM C 518 test. In fact 3" or more of cellulose over-blow can be a cure for low-performing attic batts, improving performance well beyond what could be accounted for by the addtional ~R10 itself.) But by requiring near-perfection in order to be able to perform to spec, batts are a 3rd rate way to insulate a stud cavity. Even today it's hard to find insulation contractors meticulous enough, and most homes are built without much attention to the air-sealing aspects even at the whole-house level, let alone per stud-bay, despite the (fairly wimpy) IRC 2009 prescription for <7ACH/50. The fact that it's theoretically possible to install them perfectly allows batts to squeak by from a code point of view but real-world performance rarely measures up. (Labeling batts at their pre-installed loft rather than at the compressed thickness when installed as intended seems bordering on fraud though. A low density R22 batt designed for 2x6 framing only achieves R19 when compressed to the 5.5" nominal cavity depth. An R19 batt only achieves R18. But high density R21s are actually R21 @ 5.5"- go figure?) Blown fiber insulation does much better in wall cavities than batts, as it conforms to all anomalies, fills in any holes & imperfections in the framing or sheathing, and conforms around wiring, plumbing etc. with very few gaps. Dense-packed goods does better still, by quasi-air-sealing the cavity and further reducing convection currents within the fiber layer.

Out here in the real world I've seen houses built in the 1920s that have 1/4" horse hair between sheets of heavy kraft paper woven between studs that perform AMAZINGLY well, considering the cavites were basically empty, save this paper & horse-hair air-barrier cutting the bays diagonally. But they perform more than just a little bit better once the material is ripped out and the cavities are dense packed with cellulose. I'm sure multi-layer RB in cavities would outperform vintage horse hair/paper laminates if installed with equivalently but so what? It's still a far cry from a high-performance methodology without building in a lot of layers & complexity into the system. At just about any R value, in most homes air infiltration becomes a bigger wintertime heat loss factor than conduction through wall assemblies, but in even somewhat tighter houses R value matters. RB requires air spaces to work at all, air spaces can become thermal bypasses unless the assembly is air-sealed. (Vertical air spaces have stack-effect working against it too.)

Multi-layer RB is widely available in Europe, but performance claims by manufacturers have run afoul of post-Kyoto, EN standards for U values, and watching the ongoing machinations & arguments over test methodologies etc. is like an the updated version of a bad movie plot that we've all seen before.

Thin sheet goods of any type detailed as an air barrier will improve the performance of a leaky wall cavity, but filling the cavity with a highly air-retardent and insulative bulk goods is cheap & effective. Detailing both the exterior sheathing and interior wall is a more appropriate treatment of air sealing, and combined with air-retardent cavity fill it can perform pretty much to spec without being perfect.

Greetings,
QUOTE> Fact is, most of the shortcomings of fiberglass has more to do with lack of proper air-barriers (and vapor control) than the material itself. Some of the benefits attributed to radiant barriers in wall or ceiling assemblies have as much to do with it's functioning as an air barrier than any of it's reflectivity/emissivity properties

You're so full of it. Who did you sell your degree to?
You can't seem to get the difference between RB and RI. I believe you're doing that on purpose.

Greetings,

QUOTE> 06 Dec 2011 03:28 PM
Buildings in the arctic are completely different animals from residential construction here in the lower 48. The panels needed a vapor barrier. The fact that the SeaBees experimented with a product whose spec was cancelled back in the 1980's doesn't do much to support your contentions.

Considering the results that was one successful experiment. Got their money's worth that time. If it works up there it sure is going to work down here.
The HH-I-xxxx procedure was terminated and affected alll products they used. Had nothing to do with the RI material they used. Besides RI are still used in the Arctics. Don't you watch PBS?

QUOTE> If it had not been for these illegal Gov. actions we wouldn't be talking today about FG and most likely cellulose.
I see. And what happened when the "illegal Gov. actions" went to court? More conspiracy theory, right?

You just try to challange the US Gov; INC. You apparantlely have no idea what your gov.inc is doing to you. Ignorance is bliss but eventually it turns dark, as you will see.

Besides RI are still used in the Arctics. Don't you watch PBS?

I've heard they use it on space probes, too. Is that true?

Greetings,

QUOTE> I've heard they use it on space probes, too. Is that true

Every picture you see of a satellite or shuttle, etc. you will see gold or aluminum coated mylar.
There use to be a picture of an assembly room on the web and you could see the racks of RI.

The gold is used around the nozzle area because it is not affected by the corrosive exhaust chemicals.
Pepsi used to run an ad showing one of the modules and you could see the gold foil.

My formerdoctorate brother in law was a physicist for one of the companies that built the satellites and I had a picture of him in the ass'y area with one of the satellites and a rack of alumn and gold foils was in the pic.

When you see a pic of the Hubble telescope you'll see that it is wrapped in RI.

If it wasn't for the high eff of RI there would be no space program.

And if our homes were all in outer space where 100% of heat transfer is radiated, that would be the right way to insulate houses.

Air is not vacuum.

Air isn't stationary it conducts, convects and leaks.

GREETINGS,

Quote> And if our homes were all in outer space where 100% of heat transfer is radiated, that would be the right way to insulate houses.

But up to 80% of heat gain/loss is radiant energy.

Air is not vacuum.

But RE moves at about the speed of light in it, so it doesn't matter.

Air isn't stationary it conducts, convects and leaks.

Your favorite subject which does not change the fact that RI out perform FG, cellulose and foam.

You have to be the most mis informed engineer I've ever encountered. I really do have doubts that you are an engineer. You seem to have practically no real world experience except for a few passive houses. I don't how to break this to you, but if you go out side you'll find most houses are not that type.
Sitting at a computer and researching documents does not make you an expert, except, for looking up documents.

When it comes to deciding what is best I'll take the personal experience of someone/s one who has been INVOLVED for several decades and have a proven track record.

researching documents does not make you an expert,

Speaking of documents; you have a website. Is there some reason you haven't published a copy of that cancelled "MilSpec" you keep referring to?

Greetings,

If you e-m me at [email protected] I'll see if I can find it and send it as an attachment.
The paper is off white, so I don't know how good a copy it will make.

Greetings,

I just spent the last hour or so going thru my filling cabinets, twice. Unfortunately I could not find my copy which is surprising as that is not something I would throw away. It could still be hiding down there, somewhere.

I also e-mailed the construction battalion to see if they had a copy and if I could get a copy. After 40+ years I'm not too optimistic.

OK, just let us know if you can find a copy.

Seriously, this guy is just winding us up right?

He's really good at making assertions of "facts" not in evidence (and often widely refutable), and other facts that may be factual, irrelevant to the problem (such as radiant energy traveling at the speed of light).

It is simply not factual that most of the heat transfer from the outer surfaces of a home to the inter surfaces "up to 80%" radiated (in anything but an empty-cavity but air-tight home).

Whole-house infiltration/ventilation is still a significant fraction of the heating & cooling loads of most homes, and empty cavities with air leaks on either the interior or exterior sheathing surfaces allows massive convective loss, even if there's RB center-cavity, a loss that is largely impeded by even mid-density fiber goods (and completely by expanding spray foam.) Unimpeded stud cavites are flues, with a real stack effect, driving infiltration (and increasing fire spread, but that's a whole 'nuther topic.)

A MIL spec for a product appropriate for arctic insulation while perhaps academically interesting isn't particularly relevant for most of us. Use of fiber insulation in climates where most of us live is just fine if the stackup & air sealing are attended to reasonably- at least most of the year (even most of the winter, if you do the stackup right) the temperatures within the fiber layer will be above the dew point of both the interior, and as long as air leaks & water vapor diffusion rates are reasonably controlled (and not trapped) moisture doesn't build up the the assembly. A lot of bad practices have been put to rest (excessive use of poly vapor barriers) and many better approaches (climate-approprate foam R and rainscreened siding on the exterior, modestly vapor retardent interiors, increased density of fiber insulation) that pretty much "cures" the problems associated with fiber insulation in TEMPERATE climates.

At the POLAR EXTREMES this isn't the case- the fraction of the year that the exterior of the assembly is above the dew point of the interior is small to none, and it becomes nearly impossible to air seal the interior sufficiently to keep it from eventually icing up. There is almost zero hours of drying condition temps, ergo air-tight multi-layer RB becomes a more reliable alternative. If you live in Antarctica, foam & RB may be your only real options, but where most N.Americans live there are other options, with other benefits. Even with the dubious practices of the past, most homes haven't failed due to rot or mold from use of fiber insulation.

While it's true that at circa 1980 code standards the performance is low (particularly on cheapest-approach code-min), and even a 2011 code levels going with the cheapest lowest-density fiber approach won't meet a very high standard, it doesn't take a huge uptick in installed price to build true performance into a house.

Greetings,
QUOTE> It is simply not factual that most of the heat transfer from the outer surfaces of a home to the inter surfaces "up to 80%" radiated

(in anything but an empty-cavity but air-tight home).

Yes, and that is exactly why you use RI. And guess what, it doesn't have to be fully air tight.

Quote> a loss that is largely impeded by even mid-density fiber goods

You're living in la la land.

Quote> as long as air leaks & water vapor diffusion rates are reasonably controlled (and not trapped) moisture doesn't build up the the assembly.

Again, la, la land. I've never seen such a perfect scenario and all the FG houses I've checked have condensation and MOLD. The cellulose houses have condensation.

Quote>
A MIL spec for a product appropriate for arctic insulation

It was for their standard product and I happen to have a roll of it.

QUOTE>. Even with the dubious practices of the past,

You really believe it isn't still the norm. La, la land again.