Step 2: Trim to Length

man cutting insulation batting to fit wall cavity
Photo: Ryan Benyi
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Tuck the insulation into the cavity, snug against the top of the stud bay and edges flush with the studs. The batt should not be tightly compressed against the studs; that will reduce its R-value. For an accurate fit against the bottom of the cavity, let the insulation run long, then cut it against the bottom plate of the wall framing with your utility knife.
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    Tools List

    • gloves
      gloves
    • dust mask
      dust mask
    • straightedge guide
      2x4 straightedge
    • utility knife
      utility knife
    • staple gun
      staple gun or hammer tacker
    • caulk gun
      caulk gun

    Shopping List

    1. Batt insulation
    to match the depth of the stud. To estimate how much you need, measure the square footage of each wall and subtract 10 percent.

    2. Vapor retarder
    to estimate how much you need, measure the square footage of the wall and add 5 percent.3. Silicone Sealant