Attic Insulation - Is More Better?
You may think like I used to think – 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 vapor barrier (or more accurately a vapor 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. This blog is written for homes in northern climates - the information in this blog may be irrelevant or even wrong for southern climates.
Safety First
You can check for a vapor 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 look at this EPA web site 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.
Vapor Barrier
To see if there is a vapor 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 vapor 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 vapor barrier. Tar paper may also be used as a moisture barrier. If you are missing a vapor barrier, it may not be smart to add more insulation.
Add the vapor barrier first
Painting the ceiling with a vapor barrier latex paint provides an adequate vapor barrier for residential construction. Also ensure that you seal off any air leaks in the attic around electrical wires, light fixtures, heating or air conditioning ducts, exhaust ducts, sills at the top of partitions, or any other places where warm moist air from the house can escape into the attic. This may require moving the insulation that is already in the attic. This can be a dirty, itchy, tedious, and all-around unpleasant job.
Is more insulation cost effective?
Adding insulation or adding other methods of improving energy efficiency may increase the value of your home as well as reduce your energy bill. One insulation company, that I don’t necessarily endorse, offers this energy savings calculator.
Let the professionals do it
It’s probably best for most people to hire a professional to evaluate their insulation, to determine the cost effectiveness of adding more insulation, and to do the installation itself. The same goes for adding the moisture barrier, if needed. When asking for an estimate, be sure to ask for estimates of the annual energy savings that will result.
Stay warm this winter!
References
U. S. Department of Energy Home Energy Assessment - See especially the paragraph that mentions a vapor barrier.
Insulation Institute description of vapor retarders
Energystar estimate of savings from air sealing and insulating a typical home
