Attic Insulation Calculator
Calculate how many bags of blown-in or batt insulation you need to reach your target R-value based on attic area.
Insulation Needed
Attic insulation is calculated by determining the R-value gap and the coverage per bag of insulation material.
R-Value Needed = Target R-Value - Current R-Value
Bags = Attic Area / Coverage per Bag (at needed R-value)
Recommended attic R-values (US DOE):
- Hot climates (Zone 1-3): R-30 to R-38
- Moderate climates (Zone 4): R-38 to R-49
- Cold climates (Zone 5-8): R-49 to R-60
Coverage per bag (approximate):
| Type | Per Bag at R-30 | Per Bag at R-49 |
|---|---|---|
| Blown fiberglass | 25-30 sq ft | 15-18 sq ft |
| Blown cellulose | 30-35 sq ft | 18-22 sq ft |
| Fiberglass batts | 40-80 sq ft (per roll) | Varies |
Tips:
- Measure current insulation depth: each inch of fiberglass ≈ R-2.5 to R-3.7
- Do NOT compress existing insulation
- Seal air leaks before adding insulation