You can place insulation in an attic over old insulation. However, there are some things to keep in mind: 1. If the old insulation is wet, you will need to remove it and allow the area to dry before installing new insulation. Determine the source of the moisture before any insulation is added and correct the problem. 2. Check for attic ventilation to control condensation. Make sure that exhaust vents from bathrooms, clothes dryers, and kitchens are not vented directly in the attic space. All exhaust vents should be vented to the outside. 3. Using a dense or heavier insulation over an existing insulation may result in compacting the older insulation and reducing its density and overall insulating effectiveness (R-value). 4. Before adding additional insulation, look for opportunities to air seal the attic space. Look for penetrations from light fixtures, wiring, plumbing, flue pipes, chimneys, exhaust vents, heating/cooling ducts, and the attic access hatch/door coming from the heated or cooled living space below. 5. Avoid creating a vapor barrier between the existing and the new insulation. As an example, do not install additional insulation with another vapor barrier materials such as polyethylene, foil, or kraft-paper faced glass-fiber. 6. If you discover that the existing insulation is "vermiculite" (a brown, spongy mineral-looking material), beware that it could contain the cancer-causing mineral asbestos. Since testing is the only way to know if asbestos is present, the U.S. Environmental Protection Agency recommends that occupants do not disturb the vermiculite insulation. Testing should be done by a qualified testing firm. Should testing reveal that no asbestos is present, adding additional insulation can proceed. 7. In older homes (pre-1940s) with "knob and tube wiring," before adding additional insulation look for frayed, loose, or burnt wiring. Knob and tube wiring should not be covered with additional insulation and should be inspected and replaced by a qualified electrician before adding insulation. For more information on adding insulation to a home, consult the U.S. Department of Energy link below. Insulating Existing Homes

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