Can You Put Blown Cellulose Over Fiberglass?

Inspection

• Before installing any cellulose insulation, you need to get into the area and inspect to determine if it is prepared. It is essential that the fiberglass insulation you cover is completely dry to prevent the cellulose from molding. If the fiberglass insulation is batt type then the face of the insulation should be on the bottom to prevent moisture from being trapped. Any electrical outlets need to be sealed as the cellulose fibers can enter any openings in outlets and junction boxes, causing a fire hazard.

Tools Needed

• Blowing in cellulose over fiberglass insulation is a relatively easy task, requiring only an insulation blowing machine. You can rent an insulation machine at most major home improvement stores or any major equipment rental firm. A one-day rental is sufficient as the process is short and just depends on the area and thickness of insulation required. It is ideal to have a sharp knife to open the insulation packages and a broom to sweep up any insulation that fails to enter the hopper.

Installation

• Before installing the cellulose, seal off any opening such as soffits, air vents or anywhere you do not want the insulation as it is made from small fibers than can get into virtually any opening. It is critical that anyone blowing the insulation or feeding the hopper wear a mask to prevent inhalation of the fibers. Turn on the insulation blower and start feeding in the open bundles of cellulose. Start spraying the cellulose in the areas furthest from the attic access point. Place marker sticks throughout the attic at the desired height to easily judge the insulation depth.

Results

• Blowing cellulose insulation on top of your fiberglass insulation reduces the fiberglass's R value, but dramatically increases your homes insulation value depending on how many inches you add. Cellulose insulation covers better than fiberglass batt insulation, which often has gaps along the sides at the ends where heat transfer occurs.