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Insulation Compression R-Value Calculator
Compressing a batt into a shallower cavity changes its thickness and thermal performance, but the exact result depends on insulation type and manufacturer data. This calculator applies a user-selected sensitivity to the compression percentage and reports a planning R-value. Use product-specific compressed-performance tables for construction decisions and avoid gaps, voids, or unsafe installation.
Planning estimate only. Check measurements and real-world constraints before buying materials or making a commitment.
Calculate your scenario
Change any input. Results update immediately.
Your results
Estimated installed R-value
R-21.8
Planning estimate using entered sensitivity.
Thickness compression
12.0%
Nominal thickness reduced to cavity depth.
Margin to target
1.8 R
Estimate meets the entered comparison target.
How the calculation works
The calculator applies this relationship to the inputs above. Keep every measurement in the unit shown.
Worked example
Use this example to check the calculator by hand before relying on a result.
Assumptions behind the result
- • Compression is uniform.
- • Sensitivity is product-appropriate.
- • Nominal rating is accurate.
- • Air gaps and thermal bridging are excluded.
- • Code compliance uses approved assembly data.
Mistakes that change the answer
- • Assuming R-value changes exactly with thickness.
- • Ignoring gaps and poorly fitted edges.
- • Using a generic estimate instead of manufacturer data.