R-Value Guide
Understanding insulation R-values and how to choose the right product for your climate zone and application.
Choose Your State for the Right Foam to Buy
Where you build determines how much insulation you need. Hover over your state to see the recommended R-values for your climate zone, then shop the products that meet them.
Climate Zones
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| Zone | Climate | Attic Rigid Foam CI | Wall Rigid Foam CI | Under-Slab / Floor CI |
|---|---|---|---|---|
| Zone 1 | Very Hot | Not required | No CI required | No CI required |
| Zone 2 | Hot | R-5 to R-10 CI | R-5 to R-10 CI | R-5 CI under slab |
| Zone 3 | Warm | R-5 to R-10 CI | R-5 CI (exterior sheathing) | R-5 to R-10 CI |
| Zone 4 | Mixed | R-10 CI | R-5 to R-10 CI | R-10 CI under slab |
| Zone 5 | Cool | R-10 CI | R-5 to R-10 CI | R-10 to R-15 CI |
| Zone 6 | Cold | R-10 to R-15 CI | R-10 CI | R-15 CI under slab |
| Zone 7 | Very Cold | R-15 to R-20 CI | R-10 to R-15 CI | R-15 to R-20 CI |
| Zone 8 | Subarctic | R-20+ CI | R-15 to R-20 CI | R-20+ CI under slab |
Source: U.S. Department of Energy — energy.gov/energysaver/insulation. Zones shown are the dominant IECC zone for each state; some states span multiple zones.
Quick Reference Table
| Climate Zone | Walls | Basement/Foundation | Attic |
|---|---|---|---|
| 1–2 (South) | R-13 to R-15 | R-0 to R-10 | R-30 to R-60 |
| 3 (Southeast) | R-13 to R-15 | R-5 to R-10 | R-38 to R-60 |
| 4 (Mid-Atlantic) | R-13 to R-21 | R-10 to R-15 | R-38 to R-60 |
| 5 (Midwest/Ohio) ← Our Region | R-13 to R-21 | R-15 | R-49 to R-60 |
| 6 (Northern) | R-15 to R-21 | R-15 to R-19 | R-49 to R-60 |
| 7–8 (Alaska/Canada) | R-21+ | R-15 to R-25 | R-60+ |
What is R-Value?
R-value is a measure of thermal resistance — the higher the R-value, the better the insulation's ability to resist heat flow. R-value is additive: two layers of R-5 insulation provide R-10 total. For rigid foam board insulation, R-value is determined by the material type (XPS, EPS, GPS) and thickness.
R-Value per Inch by Material
| Material | R-Value/Inch | Products |
|---|---|---|
| XPS (Extruded Polystyrene) | R-5.0 | FOAMULAR® 150, 250, 400, 600, 1000, ThermaPink® |
| GPS (Graphite Polystyrene) | R-4.7 to R-5.0 | ProBoard Ultra, HalfBack Premium |
| EPS (Expanded Polystyrene) | R-3.8 to R-4.2 | ProBoard, ProBoard Red Label |
Not Sure Which Product You Need?
Our team can help you select the right R-value and product for your specific application and climate zone.
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