How to Apply a Vapor Barrier to Attic Insulation

By: Danny Lipford

The insulation in my attic has paper backing, and I’d like to add a vapor barrier on top of it. Some people have said this is a good idea while others say it isn’t necessary. I’m confused, what should I do? -Beth

Hi Beth,

Do NOT add a vapor barrier on top of the insulation in your attic, since the paper facing on the existing insulation IS the vapor barrier. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it.

Attic insulation should always be installed with the paper backing facing toward the living space (the ceiling in this case). This acts as a barrier to keep heated, moist air from rising up into the attic during cold weather.

Adding a second vapor barrier could cause condensation to become trapped in the insulation between the two vapor barriers. Over time this trapped moisture can rot the wood framing in your attic or cause mold and mildew to appear.

If you add more insulation on top of what is already there, be sure to use unfaced batts which do not have a paper backing, or have another layer of insulation blown into your attic on top of the existing insulation.

Good luck with your project,

Danny

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2 Comments on “How to Apply a Vapor Barrier to Attic Insulation”

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  • Rosemary Says:
    June 5th, 2015 at 3:03 pm

    I had hardy plank installed on my chimney and the front of my home. I then painted the hardy plank. I now have peeling paint along one side of the chimney. There is a moisture problem. What should I be checking? I have been told the hardy plank must be sealed properly or I will have problems with it. The worst spots are at the roof line where the hardy plank meets the shingles. What must be done to solve this problem?



  • GARY Says:
    December 8th, 2014 at 12:43 pm

    I WANT TO INSTALL INSULATION IN MY ATTIC FLOOR WHICH I USE FOR STORAGE. THE PREVIOUS OWNER HAS 1″ FOAM INSULATION WITH A A PLASTIC VAPOR BARRIER ONLY ON THE RAFTERS OF THE ROOF ABOUT4″ FROM THE SLATE ROOF BUT NOT ON THE WALLS OF THE ATTIC. MY QUESTION IS SHOULD IUSE A VAPOR BARRIER INTHE ATTIC FLOOR?


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