Does anyone else just see a lawsuit when they watch this video?
I'm sorry ya'll, but I have to weigh in on this one. It is a shame that you have had no competently guided first hand experience with radiant barriers. Properly used and installed the radiant barrier is the eighth wonder of the world, the best kept secret on the planet.
As you read through this you will probably experience severe cognitive dissonance. I say this because there was a time when I based insulation efficiency on mass. I'm sure that it was mainly because that is what I saw in all installations, and thought "the thicker the better".
Radiant barrier efficacy is counterintuitive because of its mass (usually 3-5 Mils), and well as the fact that it is such a good conductor. So you just "gotta" wonder why all the forest firefighters, the extreme climbers and skiers, and the seasoned outdoorsmen, and pilots who fly in and out of the mountains all carry 1 Mil SPACE BLANKETS (radiant barriers) to protect against freezing if they are stranded. They are also excellent for football games, and will keep you nice and cozy, while those around you are turning various shades of purple.
Or you might wonder why a customer of mine in Crestone, Colorado whose house is at the 7,200' elevation level, has perforated radiant barrier as her primary method of insulation in the attic, walls, and crawlspace, albeit the house is well sealed with foam to eliminate air infiltration.
Her previously dubious contractor is now a radiant barrier disciple, as are many others whose paradigms I have had the pleasure of shifting. His biggest stumbling block was why we specified that the joists in the crawl space be covered with a solid radiant barrier rather than the "standard" 10 Mil plastic vapor barrier. I'll get to that one later.
First I feel that I must set the stage. We all know that heat ALWAYS moves to cold (under natural conditions - without the assistance of machinery or "work"). We also know that mass insulation is designed to DELAY the transfer of conductive and convective heat energy from one side of the "wall, roof, floor, etc." to the other. R-value is a function of the time it takes for one BTU to be conducted from one side of a "wall, roof, floor, etc." to the other side. The higher the R-value the longer the delay.
Radiant barrier has no R-value, because it does not delay the conduction of heat energy. Radiant barrier possesses the properties of emissivity and reflectivity, which do absolutely nothing to delay conductive or convective heat transfer. But oh what a magnificent thing it does do! It does for a building, what a thermos does for a beverage.
Question: How did the heat energy become absorbed by the insulation in the wall? How did the heat energy become absorbed in the attic insulation? How much convective heat moves laterally in a residence or office suite? How much convective heat rises in an air- conditioned environment? How is your body heat (approximately 450 BTUs per hour while working at your desk) transmitted from your desk to the room's wall, ceiling, or floor (do your feet ever get cold at your desk)? It isn't because the cold is migrating to your feet. How does the heat from the heat sink in your computer transfer to the walls and ceiling of your office?
Every body on the planet, animal, vegetable, mineral, etc. with a temperature above absolute zero radiates infrared electromagnetic waves!
The majority of heat movement or heat transfer in a residence and office space is via radiant electromagnet waves. They give off no heat while traveling at the speed of light in the building. At the point of impact upon a non-reflective solid these "photons" give up their prodigious heat.
So the thinking man posits, "what if I could manage or redirect the radiant heat before it impinged on the solid wall only to have its heat energy absorbed by the insulation, to be passed to the colder side of the "wall"?
It is a well-established scientific fact that from 50% to 80% of the heat energy in a building is a consequence of radiant heat. It can't be radiant heat because while in the infrared state, the wave gives off no heat. Its heat is surrendered when it "changes state" from a light wave to heat energy.
Reflect back when you were a youngster and held a magnifying glass over a piece of newspaper or pine straw and started a fire. That light energy (radiant heat) contained in that 1" diameter of the magnifying glass that it took 10 seconds to ignite the material, is (roughly speaking) .00694444 of the light energy (radiant heat) that hits a square foot of a roof's shingles all day long.
If I can intercept the energy that the roof re-radiates to the attic insulation and reflect it back to the roof, I have reduced the amount of heat that the attic insulation must absorb, and transfer to the interior ceiling. The Florida Solar Energy Center determined, as did Texas A&M Engineering Department that R-11 attic insulation with a radiant barrier on top of it, was at least as effective as R-19 insulation in reducing attic heat flux. The other benefit is that the interior ceiling temperature was reduced, and the ceiling temperature did not stay elevated into the night, as it had previously done.
The authorities are in accord that upwards of 85% of the summer heat gain in a residence is radiant heat impinging upon the structure and re-radiating its heat into the structure (where it is cooler).
The authorities are in accord that 50% to 75% of the winter heat loss in a residence is radiant heat migrating from the insulation to the attic (where it is cooler).
In each case one has the option of dealing with the radiant heat before it changes from its electromagnetic waveform and becomes sensible heat energy, or letting the insulation absorb the massive amounts of heat, while the air conditioner runs into the night as the heat energy in the insulation is conducted to the cooler interior of the house.
In the winter one can reflect the heat absorbed by the insulation back into the living space rather than setting it free to seek the colder air in the attic and atmosphere and create the perfect conditions for ice dams
Now for the crawl space. Does the cold from the ground migrate up to make the floor cold? Of course not - heat always goes to cold. The reason the floor is cold is because it is radiating its heat to the ground. It certainly is not conducting it, nor is the heat being convected downward. As the heat is emitted from the floor to the ground it changes state from heat energy to electromagnetic wave form (non-sensible heat). Therefore a solid radiant barrier installed in the same fashion as a vapor barrier and sealed in the same manner, does double duty. It also reflects the heat back into the home therefore reducing the amount of heat required to maintain a comfortable (and more uniform) temperature in the home.
Aluminum insulation was patented in 1925 and was used extensively throughout the north and south through the 60s and 70s until the R-value first proposed by Everett Shuman of Penn State University, got traction and established a reference to mass insulation that only delays heat transfer, sending into relative obscurity reflective insulation, which actually STOPS the transfer of heat.
The ASHRAE HANDBOOK does provide a series of calculations that establish an equivalent R-value for radiant barrier when used in an enclosed cavity such as a wall, floor joist, roof etc.
Among my favorites are the vaulted and cathedral ceilings. With three sheets of 4 Mil radiant barrier spaced ¾" apart in a 2x4 cavity, an equivalent R-value of R-50 is accomplished at only $3.00 /sq ft. installed. There is nothing else on the market today that costs less than precious metals that will do the same. On a 100+ degree-day the ceiling temperature does not exceed 80 degrees F.
I always have a ball with my mock up at the home shows. Lots of head scratching and "could you show me that again please".
I'll be happy to back up any and all of the above, and I'll even send you some samples and give you a few ways to verify the value of the radiant barrier for yourself.
I get tons of business from local home inspectors who have first hand experience with the radiant barrier "magic shows".
Once you identify an application for it, you will welcome a knowledgeable provider into your home. Radiant barrier won't do everything in a home, and there is little that it cannot do as well or better and more cost effective than the other market offerings.
Like Will Rogers said, "It ain't what you don't know that hurts you, it's what you know that just ain't so!"
According to the U.S. Department of Energy’s Energy Efficiency and Renewable Energy Clearinghouse, “Two field tests, one in Minnesota and one in Canada, both found that a radiant barrier placed over R-19 attic floor insulation (which is less than half the DOE minimum recommendation for those climates), found that the radiant barrier contributed to less than a 1% reduction in energy consumption for heating and cooling.”
Please feel free to post your real world studies. Maybe the radiant barrier community should rally to publish a study for cold climate heating savings which is based on actual homes retrofitted only with a radiant barrier to compute pre/post energy consumption. As we know, demonstration boxes and laboratory studies are one thing, real world measured performance is another.
I found this piece entertaining http://www.greenbuildingadvisor.com/blogs/dept/musings/insulating-p...
P2000 is an EPS insulation with reflective facers that has a thermal resistance within general expectations for
this type of foam insulation. Samples analyzed at CCHRC using ASTM Standard Test Method C 518‐04 provided an R‐value per inch of 4.02hr∙ft2∙°F/BTU. This compares well to the manufacturer’s stated R‐value per inch of 4.17hr∙ft2∙°F/BTU. Introducing a one‐inch air gap between gypsum board and one inch of P2000 with the
reflective surface facing the air gap increased the R‐value by 1.69 hr∙ft2∙°F/BTU to 5.71hr∙ft2∙°F/BTU. This
increase in thermal resistance introduced by the reflective insulation component is slightly less than predicted
by common reference sources. R‐Tech® EPS insulation was evaluated using the same methods.. The sample of RTech analyzed at CCHRC was found to have an R‐value per inch of 3.87hr∙ft2∙°F/BTU, very close to the
manufacturer’s stated R‐value of 3.85hr∙ft2∙°F/BTU. When an air gap was introduced, as described above, the Rvalue increased by 1.64 to 5.51hr∙ft2∙°F/BTU. In terms of the overall R‐value of a wall assembly, this is a relatively insignificant contribution, especially in cold climates like Alaska where the minimum prescriptive R‐values for wall construction range from R‐ 20 to R‐35 (AHFC, 2010). Based on samples analyzed by CCHRC, there was no evidence that P2000 would deliver substantially greater thermal performance than expected for typical EPS insulation.
In cold climate construction, when considering the use of reflective insulation to reduce heat loss, the potential
is very modest. In a tightly controlled laboratory setting, where the temperature difference is 40°F and the heat
flow direction is up, the reflective facer adds a small increase to the R‐value. When there is an air gap present,
Reflective Insulation s in Cold Climates the reflective facer has a greater effect on the R‐value of the structure by creating a “reflective insulation” as defined by RIMA‐I (2002). The actual R‐value of an installed reflective insulation is hard to determine reliably, and common calculation methods grossly overestimate R‐values. Additionally, maintaining thermal performance means ensuring the reflective surfaces are protected from penetration or surface contamination. Using reflective insulation in cold climate construction is also complicated by the vapor impermeability of the reflective surfaces, which adds potential moisture control problems to a structure if not placed properly. Simply put, the contribution of reflective insulation to the building envelope in cold climate construction is minimal, especially when viewed in the context of the total R‐value of the building envelope.
Jerry that is a lot of twisting of facts. Radiant barriers work on one of the 3 methods of heat transfer. It does nothing to stop convection or conduction. So it works during daylight hours when the sun is beating down on a roof.
Radiant barriers work the best when the temperature differential is the greatest and when a surface gives off more of its heat via radiation. So it works reasonable well in a forest fire when a flash fire quickly blows over a firefighter. But if it was a long term situation convection would overwhelm the person.
If you read studies such as those at the Florida Solar Energy Center an Oak Ridge NL you will get a much different picture than what you painted. Studies have show that in the south that there are times when a radiant barrier may appear to be effective. But looking closer at the data it is older under insulated homes. Homes with an R value of less than 19. That is about 1/2 of current code. The homes that had an R value of above 30 showed very little benefit, so little that it was not cost effective.
Some studies have show that radiant barriers loose much of their effectiveness when placed on the attic floor due to dust accumulation.
What should a person do? I would start off with air sealing. That is the best thing anyone can do. Insulation does not perform well when there is air leaks. Then I would cap off the insulation with cellulose. Fiberglass is very air porous. This openness allows radiant heat to penetrate the insulation plus insulation need to trap air and fiberglass needs an enclosure to trap the air. Cellulose on the other hand blocks but does not reflect the radiant heat. It is easy and cheep enough to add enough insulation to be effective, Also is it much better at stopping air flow.
it has been shown that radiant barriers in walls are not very effective per the FSEC studies.
I have seen homes that have installed radiant barriers in the attic. They didnt address the bigger picture of air sealing and increasing insulation. Considering that these people were charged a $1.50 to $2/sf it was a monumental waste of money.
Show me how many building science experts relay on radiant barriers. All of them espouse air sealing and lots of insulation.
This is a great read http://www.greenbuildingadvisor.com/blogs/dept/musings/radiant-barr...
Robert: It is easy to see that your experience with radiant barriers is limited to what you have read. It is obvious that you have NOT read between the lines. For every study you provide - I can provide its opposite. Further I can show you how YOU can do the test and YOU can measure the results, and YOU can be the judge.
The fact you state about radiant barrier works only on the radiant component of heat and not the conductive and convective is very accurate. What is also true is the composition of heat gain and heat loss in a building is ARE YOU READY????????????? 50% to 80% radiant heat. What is also true is that mass insulation ABSORBS HEAT ENERGY and that energy then migrates to the COOLEST place it can find when the sun goes down. READ ceiling of the residence or office space. All you have to do to prove that is take ceiling temperature readings throughout the night, and record A/C run time. Do the same thing when a radiant barrier is properly installed -GUESS WHAT HAPPENS TO THE READINGS???!!!
I first ask you to be specific about which facts I have twisted. Please list the fact(s) I "twisted" with specificity, and state the TRUE fact as regards the matter. Absent so doing - you are admitting that you are making generalizations and trying to step around REAL DEMONSTRABLE RESULTS.
You left out some cogent radiant barrier studies that showed how well radiant barrier augments fiberglass and other mass insulation whose performances are severely compromised when the humidity rises over 75% relative, and whose performance rapidly deteriorates over 90 degrees F.
By the way - I offer you a friendly challenge to show one study that DOCUMENTS the deterioration of radiant barrier performance when placed on the attic floor due to dust accumulation. It doesn't exist. I will be happy to provide tests from acknowledged Government agencies (Federal and State) as well as prestigious engineering universities that DOCUMENT that a radiant barrier placed on top of the attic insulation is 5% more efficient than stapling the barrier to the rafters.
For the record - the comments in the studies you mention are obiter dictum , commentary and opinion only - and no documentation. There has recently been such a study in which fine sand was spread on the radiant barrier - there was no deterioration in performance until the mass of the sand (a magnitude far in excess of dust particle accumulation) exceeded any dust found in any attic.
I understand that you have seen questionable installations in homes - and by right they will not do the job that they were intended to. That is not the fault of the radiant barrier.
I do not know about the FSEC studies about radiant barrier in walls not being effective. Nor am I aware of the metrics of the study. I can however, provide evidence of several walls with radiant barrier installed instead of mass insulation, that control ambient temperature and DRASTICALLY reduce the heat gain in the summer and the heat loss in the winter. These installations are predicated on thorough sealing and elimination of air infiltration.
Are you asserting that after the sun goes down - there is no radiant heat left to deal with in a building?
Again Robert - Please post with specificity the facts you allege that I have twisted, and I'll humbly retract my statements. Absent the posting - they stand as truth.
Thanks for your comments