How Not to Insulate Your Attic

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Thinking about putting some (or some more) insulation in your attic? This guide can help.

Although installing insulation in an unheated attic is usually a fairly straightforward job, a variety of pitfalls await the unwary. So, with cold weather approaching in most parts of the country, we present this Chamber of Horrors of atticinsulation mistakes, maladies, and oversights. Look it over, and then pay a critical visit to your own attic—if you dare.

Vent Areas Blocked in the Eaves

Don't push batt or blanket insulation past the top plate at the end of joist runs . . . or fold it back and up between the rafters . . . or pour fill insulation into such areas. If you do, you'll obstruct the flow of air from soft-it vents (or, in older homes, from gaps between the outer wall and the roof). In fact, if your roof's pitch is steep enough to allow access to the eaves, you can install a slanted-board baffle at the end of each joist run to prevent insulation from clogging the area.

Holes and Gaps in the Attic Floor

Fill in the extra space around openings where pipes, ducts, and wires enter the attic floor, using unfaced fiberglass or caulk. Caulk nail and drill holes, as well.

Recessed Lighting Fixtures Covered with Insulation

Recessed lighting fixtures that are covered with insulation become extremely hot and present a serious fire hazard. So maintain a minimum clearance of three inches between recessed fixtures and any kind of insulation. Be particularly careful when using poured or blown-in cellulose, which over time can drift onto recessed fixtures. Yes, open spaces do allow some heat to enter the attic, but the cost of the wasted heat is nothing compared to that of a fire. Furthermore, there is an alternative: Replace the fixtures with flush-mounted lighting.

Vapor Barrier Placed Wrong Side Up

Install foil- or paper-faced insulation with the facing side down. If the facing is up, moisture will become trapped in your insulation and turn it into an ineffective mess. If you use loose-fill insulation, you may need to install a vapor barrier of polyethylene sheeting between each joist run before you pour the material, or to coat the interior ceiling below with a vapor-retardant paint.