Can You Install Roll Insulation on Top of Blown Insulation?

Blown-in Attics

• Most attics are insulated initially with some type of blown-in insulation, usually cellulose, fiberglass or rock wool. This type of insulation is granules or pellets spread between joists in an attic with some type of air blower. It is usually installed during initial construction. Over time, the granules or pellets can compress or get scattered so the insulation becomes less solid and less effective.

Fiberglass

• A common way to add attic insulation is with fiberglass batts or rolls, usually 16 to 24 inches wide. Batts are long strips; rolls are just that -- sheets of fiberglass rolled up for easier handling. The insulating material is glass fibers spun into a cushion, usually 4 or 6 inches thick. It is installed in attics without fastening, simply laid across the roof joists.

Unfaced

• Always use unfaced fiberglass rolls when covering blown-in insulation. Faced rolls have a vapor or moisture barrier that can create moisture problems when installed on top of blown-in insulation. Carry rolls into the attic and unroll them across the joists so the wood supports the fiberglass. Use big shears or a utility knife to cut rolls at the edges of the attic.

Air Gap

• Cover the entire attic area, making sure the roll ends get to the eaves of the roof. Don't lay fiberglass rolls directly on blown-in insulation in a way that it would compress or condense the granules or pellets. Allow a slight air gap between the top of the blown-in insulation and fiberglass so the fiberglass does not compress or condense the blown-in granules or pellets.