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I have a 1-story dwelling with an attic (cold space) that has approx. R-30 insulation

I have a 1-story dwelling with an attic (cold space) that has approx. R-30 insulation but NO plastic vapor barrier between the sheetrock and the insulation....

I am considering adding a radiant foil barrier on top of the the blown insulation.
What are potential problems could I have, as a result of this installation? Moisture problems? Our home is in Northfield, MN 55057

Asked by gary schutte
Posted Aug 27, 2014 1:52 PM ET
Edited Aug 27, 2014 3:31 PM ET


3 Answers

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Don't do it.

Foil is a true vapor barrier, less than 0.05 perms, and if located on the cold side of the assembly even vapor diffusion is enough to create wet/frozen insulation in your climate at the top layers if you trap it.

The thermal benefit of a foil radiant barrier is truly miniscule in a MN climate too- you're far better off spending the money on air sealing & insulation.

Answered by Dana Dorsett
Posted Aug 27, 2014 2:11 PM ET


Dana is right on both points.

A radiant barrier on top of your attic insulation will make the top layer of insulation damp.

You'll get much more of a performance improvement by spending the same amount of money on deeper insulation. (Of course, if you haven't sealed the leaks in your ceiling yet, that work always comes first.)

Answered by Martin Holladay
Posted Aug 27, 2014 3:26 PM ET


For more information on air sealing, see Air Sealing an Attic.

For more information on radiant barriers, see Radiant Barriers: A Solution in Search of a Problem.

Answered by Martin Holladay
Posted Aug 27, 2014 3:51 PM ET

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