Radiant barrier questions

I have a couple questions for the experts on radiant barriers.
1. Are they worth the expense in reducing utility bills in a hot climate?
2. Is there a preference between the paint and a physical barrier stapled to the rafters.
It seems that using a physical barrier on the rafters would block air flow.
Suggestions please. Thanks in advance.
Bob-tx
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I've never seen hard, actual data that proves they are, but the consensus does appear to be that they work and are worth the cost. The material is maybe $100-200 for a typical attic, which you should recover relatively quickly if you use AC in an area that gets reasonably hot.

I've only seen either the stapled type or else the similar type that is already applied to sheathing. Never knew paint type existed. If you have 2 people, IMO, it's going to be a lot easier, cleaner, faster to staple.

You leave an open area of a foot or so at the bottom and the top. This leaves plenty of space for air to enter at the bottom and exit at the top, preferably through a ridge vent. If you don't have a ridge vent, then I would think it could impact air flow through a gable vent, etc.

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wrote:

I agree with trader and suspect that the physical barriers would work better since they would create a separate air space as well and that would increase the insulation. Remember you want to keep the shinny side clean.
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Joseph Meehan wrote:

You want to keep one side that adjoins free air clean. I don't think it really matters whether it's the shiny side or not.
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Yes, it need to be the shiny side. A radiant barrier is a shiny surface with an air gap next to it (so there is no conduction). If the shiny surface gets dusty, then you no longer have a radiant barrier.
Cheers, Wayne
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Bob wrote:

yes
probably, but you don't cover 100%, especially at the top and bottom, so air will still circulate

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...
Very good and very important point.
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