Radiant Barrier Over Fiberglass


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Old 10-14-07, 08:46 AM
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Radiant Barrier Over Fiberglass

Hi: I am planning to lay a radiant barrier--product is two sided aluminum foil which is polyester mesh reinforced, over existing blown fiberglass insulation.
Product comes 48" wide, and is perforated for moisture transport across the barrier. 97 % Reflectivity.
Assume I have sufficient blown fiberglass insulation. We live in Charlotte, NC. Roof is dark shingles, has ridge vents and an attic fan. We believe the radiant heat penetrates to attic space, which becomes a heat sink and eventually penetrates to living space below. Are we correct in thinking the radiant barrier will largely prevent that? The cost for 2000 sq.ft is under $400. Have I thought this out correctly?
 
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Old 10-14-07, 02:01 PM
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Once your RB gets a layer of dust on it it will only be able to reflect a very small portion of the radiant heat back. In a existing home paint is a better option.
 
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Old 10-14-07, 02:23 PM
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Airman:Having read about the radient chips that can be blown in regarding the dust situation, we put a sheet of foil in the attic six months ago. There was virtually no dust on the test piece. I would guess it would take dust covering a large area of the barrier to negate the reflectivity. At least that's one idea! But thanks for replying.
 
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Old 10-14-07, 02:59 PM
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I would think that if you did not collect dust on the aluminum foil then you may not have enough ventilation.

What is the total area of the ridge vents, do you have continuous ventilated soffits and is there a clear path for the air from the soffits?
The vent fan will do little if you don't have ventilated soffits.

Your money will be better spent if you create more air movement and/or add more insulation.
 
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Old 10-14-07, 06:10 PM
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Studyes say about 2 years and the the RB sheets drop way off. This will be a very light coating of dust but that is all it takes.
 
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Old 10-15-07, 02:52 PM
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Radiant Barrier over Insulation

Hi: Well if the two year figure is a good working number and if I flip the film after two years and get another two years from the clean side I will have averaged less than $40 per year. I'm guessing that my savings in heat reflection in summer and perhaps a modest saving in heat retention in winter will be several times the $40.
 
 

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