Is adding more attic insulation always good?
You may think like I used to think – here in Wisconsin, adding more insulation to my attic is a no-brainer. The more insulation the better!?But in an old home, that’s not necessarily true.?An older home may not have a moisture barrier (or more accurately a "moisture retarder") between the inside of the home and the insulation in the attic.?If this is the case, adding more insulation in the attic can cause water to condense inside the insulation, and that will lower the effectiveness of the insulation, and could even damage your attic.
You can check for a moisture barrier easily, but safety first!?Wear long sleeves, protective gloves, and a dust mask. (An N-95 or KN-95 COVID mask works fine for a dust mask).?If you suspect that the attic insulation is asbestos, DON’T proceed – asbestos is toxic if breathed.?You can search the internet for “asbestos insulation pictures” to see examples of what asbestos insulation looks like.?Asbestos insulation was used for attic insulation in the U.S. from about 1900 to 1989.?Asbestos should only be handled by trained professionals.
To see if there is a moisture barrier, if the insulation is loose-fill, move some of the insulation aside to see if a plastic sheet is at the bottom of the insulation, resting on top of the ceiling.?This plastic sheet is a moisture barrier. If you have mineral wool or fiberglass batts, move the edge of the insulation to see if there is Kraft paper at the bottom.?Kraft paper looks like a brown paper bag on one side (toward the inside of the house), and often has a glossy black surface toward the insulation.?This Kraft paper is the moisture barrier.?If you are missing a moisture barrier, it may not be smart to add more insulation.?
It’s best if the moisture barrier is right against the ceiling with all of the insulation on the other side.?But it is acceptable for the moisture barrier to be anywhere in the bottom 1/3 of the thickness of the insulation.?For example, if the insulation is 12 inches deep, the moisture barrier could be up to 4 inches away from the ceiling.
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It is often more effective to seal the attic for moisture leaks than to add more insulation.?Adding insulation can be done after sealing for moisture.?But sealing an attic for moisture is a dirty, itchy, unpleasant job.?
It’s probably best for most people to hire a professional to evaluate their insulation, to determine the cost effectiveness of adding more insulation or of adding other methods of improving energy efficiency, and to do the installation itself.?When asking for an estimate, be sure to ask for estimates of the annual energy savings that will result.?Adding insulation or adding other methods of improving energy efficiency is often cost effective only if you plan on living in the home for many years, or if the existing energy efficiency is significantly inadequate.
By the way, this article assumes you live in a cold climate like Wisconsin. Some of the considerations change if you live in a hot or a very humid climate.
Stay warm this winter!