Unfaced insulation

Unfaced insulation is a blanket insulation product, usually made of fiberglass, but sometimes made of cotton, sheep's wool, mineral wool, plastic, or other materials.

Unfaced Insulation
Insulation with no attached vapor barrier.
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Unfaced Insulation - Insulation with no attached vapor retarder.
Vapor Retarder - Helps control the amount of moisture passing through the insulation and collecting inside exterior walls, ceilings and floors.

Buy unfaced insulation to lay on top. You don't need to replace the other stuff first.

To do this, use an unfaced insulation with no paper moisture barrier. Once you're level with the joist tops, you can add more insulation by running it at right angles to the joists. This too should be unfaced material with no vapor barrier.

First measure and cut small pieces of unfaced insulation and fit them snugly into the band joist. Unfaced insulation does not have kraft paper or other material on one side of the fiberglass insulation batts as shown in Figures 2 & 3.

Though insulation can either be covered with a facing material or left open-faced (meaning the fluffy fibers are exposed), unfaced insulation is the best choice when adding to existing attic insulation.

Since both the attic above and room below will be heated, you can use unfaced insulation without a vapor barrier or no insulation at all. Read on to find out more.
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Importance of Proper Attic Ventilation ...

Plastic film used to prevent moisture from passing through unfaced insulation. Both 4- and 6-mil polyethylene are preferred because they are less likely to be damaged during construction.
Polyisocyanurate Foam ...

When plastic sheeting is used as a vapor barrier, unfaced insulation is held in place as sheeting is stapled over framing studs.

Polyethylene Vapor Barrier - Plastic film used to prevent moisture from passing through unfaced insulation. Both 4- and 6-mil polyethylene are preferred because they are less likely to be damaged during construction.

PVC jackets are durable, attractive, and an easy-to-clean material that is typically field-applied over unfaced insulation and most factory-applied jackets where additional protection is necessary.

See also: Insulation, Home, Floor, Faced insulation, Heating