Insulation R-Value by Location
| Location | Climate Zone 1-3 | Zone 4-5 | Zone 6-7 |
|---|---|---|---|
| Attic | R-30 to R-38 | R-38 to R-49 | R-49 to R-60 |
| Walls (2Γ4) | R-13 | R-13 to R-15 | R-13 + R-5 sheathing |
| Walls (2Γ6) | R-19 | R-19 to R-21 | R-19 + R-5 sheathing |
| Floor | R-13 | R-25 | R-30 |
Insulation Calculator
Calculate how much insulation you need by area and desired R-value. Covers batts, blown-in, and spray foam.
π How We Calculate — Learn about our calculation methodology, data sources, and quality standards.
Frequently Asked Questions
What does R-value mean?
R-value measures thermal resistance. Higher R = better insulation. It is the inverse of U-factor (heat flow rate). R-38 blocks roughly 97% of heat transfer.
Which insulation is best?
Closed-cell spray foam has the highest R-value per inch (R-6.5) and adds structural strength + vapor barrier. However, it costs 3-4Γ more than fiberglass batts.
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Open βHow to Use This Insulation Calculator
Enter the area to insulate, current insulation R-value, and target R-value. Select insulation type. The calculator estimates the amount of insulation and cost.
Formula & How It Works
R-value = thickness Γ R-per-inch. Common values: fiberglass batt R-3.2/inch, spray foam R-6.5/inch, cellulose R-3.7/inch. Total R needed = Target β Existing.
Calculation Example
Attic 1,200 sq ft, current R-11, target R-49: Add R-38. Using blown fiberglass (R-2.5/inch): need 15.2 inches depth. Material cost β $0.50/sq ft = $600.
Expert Tips
Attic insulation gives the best ROI β it is the biggest source of heat loss. R-49 to R-60 is recommended for attics in most US climate zones. Air seal first before adding insulation for maximum effectiveness.