In the sequence, which step comes directly before installing insulation?

• A. Identify and seal air leaks
• B. Inspect for gaps and seal
• C. Install vapor retarder in correct location
• D. Install insulation

Answer: (C)

Think about moisture management in the building envelope. Before you fill the cavity with insulation, you want a continuous barrier that slows or stops moisture from moving through the wall or ceiling. Installing the vapor retarder in the correct location establishes that barrier on the warm side, so moisture is kept from condensing within the insulation and inside the wall assembly. If you put insulation in first, moisture from indoor air could diffuse into it, reducing its effectiveness and promoting mold. The other steps are about preparing the space by reducing air leaks, but the step directly preceding insulation in this sequence is placing the vapor retarder.