In many cases you can add new insulation on top of old insulation, unless the old insulation is wet, mouldy, or vermiculite. If the old insulation is dry but appears to have previously been wet, you should look for the cause and repair the problem. Wet insulation should be removed or it can lead to mould, mildew or cause your ceiling or roof rafters to rot. In general, either batt or rolled insulation or blown loose-fill insulation (fiberglass or cellulose) can be installed on top of old insulation.
If you need to add new insulation on top of old insulation please note the following:
- Draftproofing should be completed prior to the addition of more insulation.
- Any new batt or roll insulation added on top of existing insulation in the attic needs to be without a vapor retarder (face). Most vapor retarders on fiberglass are made of kraft paper. The presence of this paper vapor retarder on top of between layers of insulation can trap moisture leading to mold or even rotting. Any existing batt or roll insulation in the attic should have the facing against the attic drywall floor or no facing at all.
- If your new insulation is rolled insulation, you should roll it out perpendicular to the joists. Be sure to use unfaced rolls. If you cannot find unfaced rolls, you can simply pull the kraft paper (vapor retarder) off without much loss of insulation. You should not tack down rolled insulation. Insulation need to be fluffy to block heat flow. You will reduce the R-value of the insulation by flattening it to tack it down.
- If you discover vermiculite insulation in your attic, be sure to have it tested for before doing work there. If the test reveals that asbestos is present, the vermiculite should be removed by a certified removal expert before disturbing it with the installation of more insulation.
For more information, visit ENERGY STAR®.
Did you see a building science or energy efficiency term you did not understand? Check out our glossary.