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Wall Insulation: Step-by-Step How-To Guide

Comprehensive instructions for Blown-in, Batts & Rolls, Spray Foam, and Rigid Foam Board installations for both 2x4 and 2x6 construction.

Before You Start

  • Wear PPE: gloves, long sleeves, eye protection, and a respirator or dust mask.
  • Identify your wall construction: 2x4 (3.5" cavity) or 2x6 (5.5" cavity).
  • Check for existing insulation and assess its condition.
  • Seal air leaks around outlets, switches, and windows before insulating.
  • Ensure proper vapor barrier placement per local building codes.
  • Check for electrical wiring and plumbing before drilling holes.

Blown-in Wall Insulation

Best for existing walls without removing drywall. Uses cellulose or fiberglass blown through small holes drilled in the wall.

  1. Locate wall studs using a stud finder and mark their positions.
  2. Drill 2-inch holes between studs at the top of each wall cavity.
  3. For 2x4 walls: drill holes every 16 inches; for 2x6 walls: every 24 inches.
  4. Insert the blower hose through the hole and fill cavity from bottom to top.
  5. Monitor density using a density probe to ensure proper coverage.
  6. Stop when material reaches the hole opening, then patch holes.
  7. Use drywall compound to patch holes and sand smooth when dry.
  8. Prime and paint patched areas to match existing wall finish.

Batts & Rolls Installation

Most common DIY method for new construction or when drywall is removed. Use faced batts with vapor retarder toward the living space.

  1. Measure stud spacing (typically 16" or 24" on center) and cavity depth.
  2. For 2x4 walls: use R-13 to R-15 batts; for 2x6 walls: use R-19 to R-21 batts.
  3. Cut batts to fit snugly between studs using a utility knife and straightedge.
  4. Split batts around electrical boxes, pipes, and other obstructions.
  5. Install batts with paper facing toward the living space (warm side).
  6. Staple flanges to stud faces every 6 inches, avoiding over-compression.
  7. Fill gaps around electrical boxes with small pieces of insulation.
  8. Install vapor barrier over insulation if using unfaced batts.

Spray Foam Insulation

Professional-grade insulation that expands to fill cavities completely. Best for air sealing and high R-value requirements.

  1. Hire a licensed spray foam contractor for proper installation.
  2. Choose between open-cell (R-3.5 per inch) or closed-cell (R-6 per inch) foam.
  3. For 2x4 walls: 3.5" of closed-cell provides R-21; 2x6 walls: 5.5" provides R-33.
  4. Ensure proper ventilation during application - foam releases gases.
  5. Contractor will drill holes and inject foam into wall cavities.
  6. Foam expands to fill entire cavity, sealing air leaks completely.
  7. Allow foam to cure completely before covering with drywall.
  8. Trim excess foam flush with stud faces using a saw.

Rigid Foam Board Installation

Installed on interior or exterior walls. Provides continuous insulation and reduces thermal bridging through studs.

  1. Choose foam board thickness: 1" (R-5), 2" (R-10), or 3" (R-15).
  2. For interior installation: attach directly to studs before drywall.
  3. Cut foam boards to fit between studs using a utility knife.
  4. Apply construction adhesive to stud faces for additional hold.
  5. Install foam boards snugly between studs, sealing joints with tape.
  6. For exterior installation: attach over sheathing before siding.
  7. Seal all joints and penetrations with appropriate sealant.
  8. Install drywall over interior foam or siding over exterior foam.

Pro Tips

  • Always check local building codes for vapor barrier requirements.
  • For 2x6 construction, consider higher R-value insulation for better efficiency.
  • Seal air leaks before insulating to maximize effectiveness.
  • Consider hiring professionals for spray foam and blown-in installations.

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