Insulation Calculator

Calculate attic floor area (length × width), accounting for obstructions. Most climates need R-30 to R-49 in attics. For 1,200 sq ft attic at R-38: about 40-45 bags of blown cellulose (covering 30 sq ft at R-38 each). Add existing R-value to new insulation for total. Check local energy codes for minimum requirements—they vary by climate zone.

US Energy Code recommendations: Zone 1-2 (hot): R-30 attic, R-13 walls; Zone 3-4 (moderate): R-38 attic, R-13-15 walls; Zone 5-6 (cold): R-49 attic, R-20+ walls; Zone 7-8 (very cold): R-49-60 attic, R-21+ walls. Higher R-value in attics is most cost-effective. Walls are limited by stud depth. Always meet or exceed local building codes.

Insulation costs: USA $0.30-1.50/sq ft DIY, $1-3/sq ft installed; Canada C$0.50-2/sq ft; UK £5-25/m²; Australia A$5-15/m². Blown cellulose is cheapest for attics. Fiberglass batts are economical for walls. Spray foam costs 2-3× more but provides air sealing. ROI typically 2-5 years through energy savings.

Batts work best for standard stud spacing (16" or 24" OC) in walls and floors—easy DIY installation. Rolls are similar but more economical for large areas. Blown-in (cellulose or fiberglass) is ideal for attics—fills irregular spaces, works over existing insulation, requires machine rental. Spray foam is best for air sealing and tight spaces but professional-only.

Yes, adding insulation is common—R-values are additive. If you have R-19, adding R-30 gives R-49 total. For attics, blown-in over existing batts works well. Run new insulation perpendicular to joists to cover thermal bridges. Remove vapor barrier on new material when adding over existing. Check existing insulation condition first—wet or compressed insulation should be replaced.

In cold climates, vapor barrier faces the warm (interior) side of walls. In hot-humid climates, it faces exterior or is omitted. Faced insulation has paper vapor retarder attached. Never sandwich insulation between two vapor barriers—causes moisture trap. Attic floors often don't need vapor barrier. Check local codes—requirements vary significantly by climate zone.