You probably already have some insulation in your attic and may want to increase your R-value. Are you wondering whether it is possible to add new attic insulation over existing insulation? It is possible, and you probably should not have to remove your existing layer to get more out of insulating your attic.
When can you add new insulation over the existing one?
You may only have a new layer installed if the older one is not wet. If the existing layer appears to be wet, you need to have this layer removed and the source of the leak identified and fixed. Wet insulation leads to structure damage, wood rot, mildew and mold development, not to mention a foul smell and colder temperatures in your living space.
Faced insulation cannot be placed over existing insulation in your attic. If you have any new batts or rolls, they need not to have a ‘face’ or a vapor retarder. This face may trap water if it is located between or on top of layers of insulation. Any faced insulation should have its face against the drywall floor of the attic, with any additional layers not having any vapor barriers.
You can readily install batt or rolled insulation over existing layers, so long as they are rolled out perpendicular to the joists and have no attached vapor retarders. You also want to avoid tacking down the rolled insulation, as this will reduce its R-value. Blown-in insulation is most probably the easiest insulation to install over an existing layer.
Conclusion:
Before you install any new layers, you need to have a thorough inspection of your attic to ensure that the reduction in insulation is not being caused by any other factors, such as wetness or disturbance by rodents. Also, ensure that you air-seal the attic before installation to ensure that you get the best performance from your new layers.