To install fiberglass batts over existing insulation, lay the batts perpendicular to the joists so they do not compress the insulation below.
To install fiberglass batts over existing insulation, lay the batts perpendicular to the joists so they do not compress the insulation below
Whether you live in a warm-weather state, as I do, or in a cooler northern climate, it's hard to stay comfortable and keep your energy bills in check if you don't have adequate insulation in the attic. But many homeowners I talk with don't know how much is enough.

The answer depends on where you live. Typically, houses in warm-weather states should have an R-38 insulation in the attic, whereas houses in cold climates should have R-49. These insulation levels will keep heated air from migrating out in winter. In a cooling climate, a good blanket of attic insulation helps keep the house cooler and reduces the load on air-conditioning equipment.

Most attics are insulated with blown-in loose cellulose (R-3.5 per inch), blown-in loose fiberglass (R-2.5 per inch) or fiberglass batts (R-3.2 per inch). Cellulose is recycled newsprint treated with a fire retardant. Fiberglass is just that--thin fibers of glass that trap air.

To determine if you need more insulation, measure what's in place with a ruler or tape. The chart included below shows you the approximate thickness of each type of insulation you should ideally have in the attic. When you do the measuring, make sure you have plenty of light to work by, and work on a cool day. And be careful not to step through the ceiling.

You can install fiberglass batts yourself right over existing insulation, but follow these precautions:
• Wear a long-sleeve shirt, gloves, eye protection and a dust mask.
• Make sure you use an unfaced batt (one without a paper or foil layer) so the insulation does not trap moisture in the ceiling.
• Lay the batts perpendicular to the joists so they do not compress the insulation below.
• Don't cover can lights unless they are rated for contact with insulation. It's safer to build a small enclosure with hardware cloth or plywood to keep loose insulation away from lights and exhaust fans.
• Use cardboard or rigid-foam baffles to keep soffit vents open.
• Fill all cracks between the living area and the attic with caulk or expanding foam.

A tightly sealed house is just as important as insulation. If you decide on loose-fill fiberglass or cellulose, consider hiring a pro to install the material. The equipment pros use blows in material at the correct density. Don't be concerned if it seems they are installing more insulation than necessary; the material will settle to the right thickness.
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