A friend has had an insulation company out and they want to spray the underside of the roof with a radiant barrier coating. Anyone have experience with that and what do you recommend? I have read about the aluminum faced sheathing, but am wondering about the coating? Thanks for any help.
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AFAIK there is no such thing as a radiant barrier coating.
however there are some Interior Radiation Control Coatings.
Florida Solar Eduction Center (Florida Solar Institute) has been a major player in studying radaint heat.
http://www.fsec.ucf.edu/en/
For years all I could find where things like this.
http://www.fsec.ucf.edu/en/publications/html/FSEC-EN-15/
"What kinds of radiant barrier materials are available?
There are many types of radiant barrier materials on the market, and more are being developed as radiant barriers become more widely used. Five generic types are most common:
* Single-sided foil (one foil side) with another material backing such as craft paper or polypropylene. Some products are further strengthened by fiber webbing sandwiched between foil and backing. The strength of the backing material is important since unreinforced foil tears very easily.
* Foil-faced roof sheathing materials (decking) that come from the manufacturer with a foil facing adhered to one side of the sheathing.
* Double-sided foil with reinforcement between the foil layers. Reinforcement may be cardboard, craft paper, mylar or fiber webbing.
* Foil-faced insulation. The insulating material may be polyisocyanurate, polyethylene"air-bubble" packing or other materials that impede heat conduction.
* Multilayered foil systems. When fully extended and installed so that the foil layers do not touch, these products also form insulating airspaces.
* radiant barrier "chips" are also manufactured and sold. This product is slightly different than a conventional sheet-type radiant barrier in that the "chips", which are blown onto the floor of the attic — typically to a depth of 3 or more inches, act as a multi-layer product with many "trapped" air pockets. These air pockets cause this product to function somewhat like traditional, fibrous insulation products. Even though this product may collect dust on its uppermost layer, the remaining layers and air spaces work to significantly reduce heat transfer through the ceiling assembly.
Some of these products may have R-values, which may be claimed only if the product was tested according to Federal Trade Commission regulations for insulation.
Although it is not by definition a radiant barrier, there is a low-emissivity paint available that can be applied directly to the underside of the roof decking. "
There might be some more update info if some one want to search for it. Now that I know the "secret" term - interior radiation control coating (IRCC). A search on that might give some more info.
I also found this discussion of radiant barriers and it mentions the paints.
http://www.hvac-talk.com/vbb/archive/index.php?t-140388.html
That lead to this.
http://www.radiantguard.com/index.asp?PageAction=Custom&ID=29
http://www.rsimag.com/rsi/What-is-radiant-barrier-paint/ArticleStandard/Article/detail/475972
Which gives some test data on a number of products.
Some "work", but not as good as the foils, but some are almost worthless.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Just say no to radiant barriers/coatings! Radiant barriers can work ... in laboratories ... and that is about it. Most applications in houses ... especially attics ... as soon as the radiant barrier gets dust on it ... there goes 90% of its benefit.
Dollar for dollar they don't do much. Don't let them sell you on the concept of an 'effective R-value'.
There is a time and place for everything. I feel radiant barrier products tend to be oversold and their performance is lacking. There must be some studies showing the degredation of RB when they get dusty ... not sure where to find it, though.
Thanks for your help. From earlier information we determined that it would definitely not be a good idea. And just logically I agree with the next message that such a coating would not work the way they say it will.
"Radiant barriers can work ... in laboratories ... and that is about it. Most applications in houses ... especially attics ... as soon as the radiant barrier gets dust on it ... there goes 90% of its benefit."
Where did this originate? Do you insulate houses and do energy audits before and after? Just guessing? Read this in PopSci? I'm curious because I've seen this type of "fact" presented before by various KIAs that had no basis in reality. Do you know what emissivity is and how changing that charachteristic of a surface can change the amount of heat it transfers?
"I feel radiant barrier products tend to be oversold and their performance is lacking." How so?
Admitedly I didn't read it in Pop Sci ... I do recall articles that I read in Energy Design Update, I believe that discussed radiant barriers. No I don't recall the specifics ... but I did retain the jist of the material I read ... a low emissivity surface ... a shiny jackknife blade sitting in the sun is a good example (lots of reflection, but little heat reflection) is affected substantially by whether that surface is contaminated by dirt.
I am no expert on emissivity, but what I've read about radiant barriers, ceramic coatings and the like is that performance is heavily dependent on the specific conditions in the field and field conditions tend to be far from the ideal conditions. I've really never heard of a design engineer feeling confident enough of a radiant barrier (talking about building applications) to rely on it in his calcs.
I'm sure there will be some degree of benefit from a radiant surface ... I've no doubt about that ... If I had foil backed OSB ... I would certainly put the shiny side down. And I may pay a little extra to buy it to do so. But I wouldn't put dollars into a special system and product specifically to do a job I couldn't guarantee performance next year.
You are quick to press me for evidence. I've non to actually hand you. You talk like you do have evidence ... care to share it?
I MOL share your opinions on this issue but have been presented with a lot of contradictory opinions and data in the past concerning this issue. As such, I tend to keep my unsubstantiated opinions to myself, being of the mind that offering incorrect or incomplete information or presenting unsubstantiated and/or disputed opinions as fact is not beneficial. I was curious if you had any real data on thie issue or were simply repeating something you heard/read and embellished.
I am always willing to hear out a sound technical argument from knowledgeable individuals. I also tend to challenge the know-it-all BS artists that seem to have answer for everything, most of which they have no direct knowledge or experience of. Time will tell if you are a Bill Hartman or a DanH.
Good points. With all due respect, when it comes to a lot of the stuff posted, a lot/most of it is personal opinion and a lot of the science end of things, people have little PERSONAL experience e.g. with testing a technology or science thoroughly ... so much of what we present is a combination of personal opinion and what we heard or read ... and of course ... as humans in communication ... 'embelish' it w/ our own personality (go figure).
No, I did not work at Oak Ridge or FSEC on testing materials. I suspect non of the people conducting those tests tested more than really a 'laboratory' type of condition (even the real houses probably didn't get tested w/ dirty radiant barriers).
I try to provide enough food for thought in an objective an unbiased manner. Provide enough information on the simple science of materials and technology to enable the poster to make a more informed decision for themselves.
Like anyone, I have my pet peaves and biases. Like anyone ... I read and interpret what I read in my own way.
Radiant barriers ... I tend to be admitedly VERY skeptical due to so many snake oil salesmen selling 'effective' R-values of 50 per inch. I took a picture outside of a business that was selling this stuff ... 1" insulation w/ R-50 it claimed! Give me a break. And the 3/8" bubble pack that makes a similar statement.
Maybe I came on a little strong. I should revise my original statement ... say no to spending extra money on radiant barrier products ... and be VERY careful if you still feel compelled to buy the product. Consider the science and the specific application. Do you feel comfortable buying the product after understanding the basic science?
Everything has its place and time ... even radiant barriers. It's finding the proper application and exploiting it to the max that make it cost worthy. Placing things in science perspective will help people make part of their decisions.
Hopefully a poster will not take my point of view w/out reading other responses as well and through the conglomeration of responses be able to sort the BS from the truly helpful information.
There is LOTS of controversy surrounding the subject of radiant barriers. Hardcore believers that understand the basic science and think ... ureka ... that's the best thing since sliced bread. I recall a number of articles in Energy Design Update relevant to this topic. That is a reputable publication that tends to be one of the more objective pubs I've run across ... although I haven't seen a copy in many years, now (it's expensive).
From what I understand (lookout!) reflective coatings must have an air space to reflect into to be effective--so that coating will be great to keep radiant heat in the attic, (for example, radiant heat from the house in winter), and it will keep the radiation that goes through it in the attic (seems like being in direct contact with a hot roof deck would allow long wave radiation to be emitted from the deck, through the coating and into the attic, and then the coating would keep that radiation from going back out , but I don't think it will be very good at keeping radiant heat out.
I would think that radiation must be emitted by the deck and the coating, otherwise a shiny wood burning stove, for instance, would never let any heat into the room.
Thanks for your help.