Q: I'd like to add insulation to a wall during a renovation. What should I keep in mind?
—Peter Wefers, North Andover, Mass.

Tom Silva replies: Filling walls with a fluffy layer of fiberglass insulation is one of the easiest and least expensive ways to make your home more energy efficient. All it takes is a utility knife, a straightedge, and a little patience to make sure the insulation completely fills the stud cavity, side to side and top to bottom, without being overly compressed. Work with batts made to match the depth of the studs and the width of the stud bays; for typical 2x4 construction, that's 3½ inches deep and 15¼ inches wide with an R-value of 15. Fiberglass is easy to cut, so if your stud spacing is irregular, buy batts that will fill the widest bays, and trim the rest to fit.

When you're ready to begin, protect your skin, eyes, and lungs by wearing a long-sleeve shirt, pants, gloves, safety glasses, and dust mask. Then follow these basic installation tips to help the work go faster and make sure your insulation does its job.
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    Tools List

    • 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