Cellulose insulation can contribute to airtightness when installed correctly; which practice enhances this benefit?

• A. Pack densely without sealing seams
• B. Use only loose-fill method
• C. Leave openings around plumbing penetrations
• D. Pack densely and seal all gaps

Answer: (D)

Airtightness with cellulose insulation comes from both dense packing and closing off every potential air path. When cellulose is blown in, it can fill many spaces, but tiny voids and seams can still let air move through if gaps aren’t sealed. Packing densely reduces the size and number of air channels within the fill, making it harder for air to travel through the insulation. However, without sealing, air can bypass the insulation through joints, penetrations, and gaps around plumbing, wires, and framing. Sealing those gaps around penetrations and seams creates a continuous air barrier. Together, dense packing and comprehensive sealing maximize airtightness. The other options either skip the sealing step, rely on loose-fill alone, or leave openings that allow air leakage.