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
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,