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Calculate insulation R-value by material and thickness. Compare against Energy Star standards.
R-value measures thermal resistance of insulation — the higher the R-value, the better the material resists heat flow through walls, attics, and floors.
| Zone | Wall | Attic | Floor |
|---|---|---|---|
| 1 (Hot-Humid) | R-13 | R-30 | R-13 |
| 2 (Hot-Humid) | R-13 | R-38 | R-13 |
| 3 (Warm) | R-13 | R-38 | R-19 |
| 4 (Mixed) | R-13 | R-49 | R-19 |
| 5 (Cold) | R-20 | R-49 | R-30 |
| 6 (Cold) | R-20 | R-49 | R-30 |
| 7-8 (Very Cold) | R-21 | R-49 | R-30 |
Formula
Total R-Value = Thickness (inches) × R-Value per InchThickness = Depth of insulation material in inches
R-Value per Inch = Thermal resistance rating per inch for the material type
Worked Example
6 inches of closed-cell spray foam in an attic
Did you know? According to the EPA, homeowners can save an average of 15% on heating and cooling costs by air sealing and adding insulation in attics, floors, and crawl spaces (source: ENERGY STAR).
Sources
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