Final answer:
To properly install new insulation over old in an attic, ensure only one vapor barrier is present, either by using unfaced insulation or removing the Kraft paper from the new insulation.
Step-by-step explanation:
When new insulation is placed directly over old insulation in the attic, it is essential to handle Kraft-faced insulation correctly. Kraft paper, which acts as a vapor barrier, should only be present on one side of the insulation layer. When additional insulation is added, it's necessary to either use insulation without Kraft paper or to remove the Kraft paper from the new insulation.
This is to prevent trapping moisture between the layers, which can lead to mold growth and reduce the effectiveness of the insulation. If the existing insulation does not have a vapor barrier, the new insulation with Kraft paper should have the paper facing down towards the living space. If the existing insulation already has a vapor barrier, use unfaced insulation for the new layer.