How to Add Insulation to Your Attic

Adding attic insulation involves choosing the right type for your climate, sealing air leaks first, then installing insulation between and over joists to achieve the recommended R-value for your region.

1. Know What You're Starting With. Use a ruler to measure the depth of existing insulation across different areas of your attic. Check for gaps, compressed areas, or damaged sections. Most homes need R-38 to R-60 depending on climate zone. If you have less than 11 inches of fiberglass or 8 inches of cellulose, you likely need more insulation.
2. Stop Heat Loss at the Source. Use caulk or weatherstripping to seal gaps around pipes, ducts, electrical boxes, and the attic hatch. Pay special attention to areas where walls meet the ceiling below. Use expanding foam for larger gaps, but avoid overfilling as it can expand significantly. This step is crucial because air leaks reduce insulation effectiveness by up to 40%.
3. Pick Your Weapon and Count. Fiberglass batts work well for standard joist spacing, blown-in cellulose or fiberglass covers irregular areas better, and rigid foam boards provide higher R-value in thin spaces. Calculate square footage by measuring length times width of your attic space. Subtract areas occupied by HVAC equipment, water heaters, or storage areas you want to keep accessible.
4. Gear Up Before You Start. Lay plywood or OSB boards across joists to create walkways and prevent stepping through drywall. Wear long sleeves, pants, gloves, safety glasses, and a dust mask or respirator. Set up proper lighting with battery-powered LED work lights. Remove or cover stored items to prevent contamination from insulation particles.
5. Layer One: Between the Joists. For batts, unroll and cut pieces 1 inch longer than joist spaces to ensure snug fit without compression. Fit around obstacles like wiring and pipes without squashing the material. For blown-in insulation, use a rented blower and start at the far end of the attic, working toward the access point. Maintain consistent depth using rulers as guides.
6. Cross-Layer for Maximum Resistance. Install the second layer running perpendicular to floor joists to eliminate thermal bridging. This layer should bring total depth to recommended R-value for your area. For batts, use unfaced insulation for second layer. For blown-in, continue adding material until you reach target depth across the entire attic floor.
7. Seal the Gateway to Efficiency. Cut rigid foam or fiberglass to fit inside the attic hatch cover. Attach with construction adhesive and seal edges with caulk. Add weatherstripping around the hatch frame to prevent air leaks. For pull-down stairs, install an insulated cover or tent system designed for attic stairs.