R-Value Calculator
Calculate total R-value for your wall or ceiling assembly
Rigid foam or mineral wool
Plywood/OSB
Fiberglass batts in stud cavity
1/2" drywall
Total R-Value
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Assembly U-Factor
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Meets Code?
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How to Use This Calculator
Total R-value determines how well your assembly resists heat flow. Our calculator adds up thermal resistance of each layer.
- Identify each material layer
- Enter R-value for each layer
- Calculator sums all R-values
- Compare against climate zone code
AI Insights
Smart analysis for your project
Smart Estimates
Our AI cross-references material costs, regional pricing, and project complexity for more accurate estimates.
Waste Optimization
AI-calculated waste factors based on project type, not flat percentages. Saves 5-15% on material costs.
Best Practices
Recommendations derived from building codes, contractor data, and thousands of completed projects.
Calculation Formula
Total R = R1 + R2 + R3 + ... (sum of all layers)
U-Factor = 1 / Total R
Frequently Asked Questions
What R-value is required by code?
IRC 2021: Walls R-20 or R-13+5ci, Ceilings R-49, Floors R-19, Basements R-15 continuous or R-19 cavity.
What is a U-factor?
U-factor measures heat transfer rate - lower is better. U = 1/R. Codes specify maximum U-factors.