Which practice most directly contributes to airtightness when installing cellulose insulation?

• A. Seal gaps and air leaks during installation
• B. Use heavier thickness
• C. Install with all gaps intentionally left open
• D. Ensure all penetrations are properly sealed with airtight sealant

Answer: (D)

A key factor for airtightness is making the air barrier continuous, so air can’t sneak through openings in the assembly. Sealing penetrations with airtight sealant directly stops those big, common leakage paths where pipes, wires, and ducts pass through walls or ceilings. When these penetrations are properly sealed, the overall enclosure becomes much more airtight, which is essential for the performance of cellulose insulation.

Sealing gaps and air leaks during installation is still important, but gaps around penetrations are the primary routes air uses to move in and out. Using more insulation thickness or leaving gaps intentionally open won’t achieve airtightness; in fact, gaps defeat it.