Upgrading Attic Insulation
Tom Silva points out some pitfalls to avoid when installing attic insulation
The blow-in insulation in my attic has deflated over the last 70 years or so. Can I lay batt insulation over it, or would it be better to blow more in?
—Leo Flerlage, Cincinnati
Either approach will work, as long as you pay attention to how the insulation is installed. If you’re adding fiberglass batts, for instance, make sure they are “unfaced.” “Faced” batts, like the one I’m reaching for with my left hand, above, have a vapor barrier that can trap moisture. That’s bad, because when insulation gets wet, it’s useless.
Also, if the roof has soffit and ridge vents, make sure the insulation doesn’t touch the underside of the roof. Leaving an air gap above the top of the insulation helps prevent ice dams in the winter and mold in the summer. That’s easy to do with batts: Just lay them at right angles to the rafters and push the batts tightly together. When putting in blow-in insulation, install foam baffles in the rafter bays first to maintain the air gap.
Now, if you’re planning to pile batts over your existing insulation, then buy some bales of blow-in to bring the insulation level up to the top edges of the joists. A leaf rake makes a good fluffing tool for the compacted bales. You can skip that step if you’re only adding blow-in stuff. (In either case, there’s no need to fluff up the old, compacted material.)
Whichever insulation you use, be sure you’re adding enough material to reach the recommended R-value for your climate. For guidance, go to Insulation Institute.
Shown: Tom Silva, near left, explains to Kevin O’Connor the options for upgrading attic insulation.