Posted By Roberth on 30 Aug 2011 01:23 AM
What is an RB going to do for air leaks. Air washing is going to negate any benefit of an RB. I dont think you can take an improperly air sealed and insulated building in an extreme climate and assume that proves the value of an RB is assinine.

Answer:  Since RB are solid foil they will act as an air barrier in most cases.  They are perforated, but the holes are very small so the air passage is minimal if any.  If you have "air washing" then you have a serious problem that would affect any insulation.
You're last sentence does not make sense.  Please clarify construction details and reference.

In the artic the extermely cold dry air contrasting with the warm moist interior air makes for a huge amount of vapor drive. For that location a properly installed vapor barrier would be required. This would keep the mositure out of the wall and allow the insualtion to perform better than a rb could. So lets talk about properly built assemblies and see which would perform better,

ANSWER:  Yes dryer but moisture is still available and if a dew point is there condensation will form, law of physics.  Now there are commecial applications, such as multi thous gallons/ cu. ft of liquid nitrogen were even with several layers of reflective mylar condensation does form and they have drainage taps to draw off the moisture.  Back to reply.  Non perf RB are VB, certainly better than plastic.  However since the RB does not condensate moisture and is an air barrier, then a separate VB is not needed.  Common VB do not prevent condensation in walls.  If the moisture is not available from the inside then the dew point will draw from the outside.  Law of physics.

Radiant barriers have been tested in wall assembiles in the south and have been deamed to be ineffective in a vertical application. Radiant barriers have been shown to be effectie in attic when stabled to the rafters, this is in areas that are primarily cooling climates. The farther north you go the less value they will have, that is they are not cost effective (put the extra money into windows etc). ORNL reports that RB's laid on the attic floor loose about 10% of thier efficiency per year becoming worthless in a few years.


ANSWER:  Yes that rumor has been floating around for a long time. Isn't it amazing RB barriers work every place else except in the south.  Does that sound logical to you?  Actually RB shoud be installed in the lower cord.  Effective is not the word for it.  How about reducing AC run time by 50% +.  North, south, RB are still 95% + eff. This is competition propaganda.  Ck emissivity chart of a mechanical engineering handbook.  If that is true then how come the Navy was able , according to one CB I talked to, reduce their heating oil consumption by about 30% when they pulled the frozen FG batts and replaced with 3 layer RB.  Actually the greater the delta T the more energy you will save.  95 % eff is 95% eff regardless what the temp is.  I have some serious ?s about ORNL.  The largest reduction in eff that I know of a RB due to dust was about 20%. 80% is is still better than 20% for foam.  Because of that report I developed a two layer sys for retrofit attics.  Regardless of time you will always have at lest two surfaces dust free.  I have had 1 layer RB retrofit in attics for many years and they seem to be doing just fine.

Radiant barriers work better in poorly insualted attics in which case a homeowner should air seal and insulate. Not good news if you are selling RB's because a well insulated and air sealed attic does not benefit from an RB except in the deep south.

ANSWER:  You really didn't say that, did you?  Where did you get all this bs. If it is used in the Arctic and on space ships, etc then why not in Minn?  Use your intelligence.  This bit of mischif originated with the mineral wool people.  Oh yes, the DOE promotes this falsehood too to discourge you from using RB.That's you USA; Llc dollars at work for you.

R value is a fluid number. The R is based on testing at a specified temp, I think about 75 degrees. The purpose of the R value test is to have a standard testing method. The R value of fiberglass will change at different temps.

Answer:  See answer below. *

The focus on is outdated. Thermal bridging and installion play a big part in how insulation performs. More testing needs to be done on the performance of wall systems. Now for RB's to be considered some very inovated system would have to be developed. RB's become conductors when in contact with other surfaces. So the wall would have to include an air gap. On top of that the air gap would to have no air leaks from either side. You would have to addressthe vapor barrier issues that would be affected by the RB.

ANSWER: RB have been on the market for at least 83 years that I know of.  I happen to get a roll of material that was manufactured in about 1927.  So I would believe that in this time period most of your concerns have been addressed.  The problem is your lack of knowledge about this subject and you're just shot gunning the subject, using old, really, really old, cliques-he that the bulk insulation people perpetuate. My understanding is that foil is the most tested material out there.  Because of its high eff it is the benchmark against which all others are tested.  Also. if you knew of all the misuse of testing standards that that place, you would be less enamoured with the published data. In case you didn't know, it's the mineral wool industry that controls the test methods in this country.  The fox guarding the hen house.

Radiant barriers work well in space because of the lack of air and that heat transfer is via radiant heat waves. On earth heat travels more through conduction and convection. That is where insulation is effective.
 ANSWER:  * WRONG WRONG WRONG.  Where do you get this stuff.  Did you take science in high school?

Please show me in the energy star sandards that show that RB's can replace insulation.

ANSWER:  Go to;  fifoil.com

If you want articles that will clear up some of this for you, send me an E-m and I will send several attachments.  [email protected]