How much insulation is needed for a 2000 square foot house depends on which parts of the house you are insulating and what R-value you are targeting, but for the attic floor alone the calculation is straightforward. A 2000 square foot attic footprint at R-49 using blown fiberglass will require about 26 to 34 bags of fiberglass depending on brand, or about 44 to 56 bags of cellulose because cellulose is denser. If you are insulating walls for a 2000 square foot two-story home with about 3500 square feet of wall area, you would need about 3500 square feet of R-13 to R-15 batts for 2x4 walls or R-20 to R-23 for 2x6 walls, plus additional insulation for floors, rim joists, and crawlspaces. For a full new build to modern code, you might need roughly 5000 to 7000 square feet of insulation materials total across attic, walls, and floors when counting all surfaces. The cost for just attic insulation for 2000 square feet professionally installed ranges from $2000 to $4000 for blown fiberglass or cellulose to reach R-49, while spray foam for the entire envelope could be $12000 to $20000. Always use the bag coverage charts and add 10 percent waste.
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