Spray Radiant Coating vs. Foil Retro Fit~HELP!


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Old 07-23-10, 12:29 PM
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Spray Radiant Coating vs. Foil Retro Fit~HELP!

I have been getting some bids for radiant barrier applications for an existing home e.g. a retrofit application. I am getting confused. For a retrofit application, some recommend spray coatings (provided we use the best spray which I believe to have .19 emissivity) vs. stapling foil to the rafters. We were told because of the air space between the rafters with the stapled foil, that we would be better off to have the IRCC sprayed directly to the roof decking (again, using only the best spray). We live in N TX, 2 story home built in '99, ~3900 sq. feet. These same companies state that if we were doing a new build, then of course they would definitely recommend using the panels with radiant barrier as roof decking. Another question: If using the spray, is it best to also spray the rafters and not JUST the decking?

I have done much research on the internet, but again still not able to come to a conclusion as to which is better for a retrofit app. I know to stick to the sites that have no agenda e.g. selling a product or service, but still struggling with a definitive conclusion.

Does anyone have any insight? Or, any web sites that you would recommend? I have looked at Reflective Insulation, Radiant Barrier Insulation, Radiant Barrier Reflective Insulation; RIMA-I (Reflective Insulation Manufacturers Association International). and the gov't energy web site.

TIA
 
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Old 07-23-10, 04:45 PM
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I read the handbook on that web site. Based on that information it seems like the spray is probably what is right for you. The spray coatings are not as good as the other radiant barrier systems, but reduce the radiation quite a bit. It's also really important to have the proper air space when using a barrier vs.a spray coating.

As for spraying the rafters, if they say it doesn't need to be done, I wouldn't do it. In that handbook they show retrofit barriers to be applied between the rafters as well. I'm sure they will do it if you insist on it.
 
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Old 07-23-10, 05:05 PM
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Radiant barriers are only part of the equation. To keep your house cool, you must reduce the temperature of your attic and that will still require good ventilation. The radiant barrier will reduce the heat transfer from the roof deck to the ceiling below, but it will actually increase the roof temperature. Circulating air (convection) will still heat up the attic and pass heat through to your home.

If you have and exposed ducts or ac equipment up there, be sure they are air sealed and well insulated.

bud
 
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Old 07-29-10, 10:52 AM
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I live in NTX also and did mine in winter/spring 08 with the attic foil. Radiant Barrier Foil Insulation Do-It-Yourself Radiant Barrier Tips
A rep from Efficient Attic Systems came out to see if they could spray the areas I couldn't access (about 1/3 of attic).
He said the foil was superior and was impressed by the low temp up there on such a hot afternoon.
If you go with spray application, make sure they don't go 'cheap' and water down the product so it will go further. Once I figure out how to access my 'hot' area, I'll be adding foil there too. Foil + adequate ventilation + 20" insulation is the way I'd go. My 2 cents!
As far as spraying the rafters, I'd want the top couple feet sprayed also, as these absorb heat directly from decking and radiate it to plenum/insulation/ductwork, etc. I'd definitely go with more spray than less.
 
 

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