radiant heat barrier question


I'm trying to understand what the difference is between the high dollar stuff that these insulating companies sell and plain aluminum foil, other than the reflectivity might be higher. Right now I'm thinking about just trying an experiment with a few boxes of aluminum foil by stapling it to the rafters with the reflective side toward the roof. Please let me know the fallacies of this if there are any. Thanks in advance. B
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Brian O wrote:

The plain foil might not be quite as sturdy or easy to install.
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Brian O wrote:

The professional stuff is bonded to a strong backing. Much easier to work with.
Don't expect too much from the stuff. It can help but the advantage decreases with age as dust forms on the surface.
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Joseph Meehan

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Joseph Meehan wrote:

That's why you mount it shiny side down.
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to
But if you mount it shiny side down, that defeats the purpose of keeping the radiant heat from your roof out of the house. In that case it would only work in the winter, as in summer the heat would still penetrate from the outside. Am I correct on that? B
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No. It still works well in summertime, with R8-14. It will only provide about R2 in wintertime, in either configuration.
Nick
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Brian O wrote:

No.
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<snip>
I've heard of shiny side down too but it doesn't make sense to me either. I bought the paper backed foil that is applied to a house before vinyl siding is put on. Joe's right about the degadation of the reflectivity due to dust but in addition to that there is oxidation of the foil, which is quite thin. After 10 years up there I don't believe that it's doing much good. For that matter, I don't feel that it ever did any good. One caveat on my application, however. I laid the foil on top of the insulation batts and not to the rafters as the OP notes. That may make a bigger difference since the foil would be closer to the source of the radiated energy. It has been my thought that foil applied to the rafters would degrade the shingles more quickly. Just a tought.
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