The R-value measures how well a material resists the flow of heat. A higher R-value indicates greater resistance to heat transfer, meaning the material is a better insulator. It’s a crucial factor in determining the thermal performance of insulation in buildings and other applications.
Explain It To Me: Here’s a brief overview of the zones and general insulation levels from the IRC. The International Residential Code (IRC) divides the United States into eight climate zones to help determine appropriate building insulation levels. Each zone corresponds to a region with similar heating and cooling needs. The R-value requirements for different building components (like walls, attics, and floors) vary depending on the climate zone.
| Climate Zone | Attic R-Value (Uninsulated) | Attic R-Value (Existing Insulation) | Wood Frame Walls (Min. R-Value) | Basement Wall R-Value | Slab R-Value | Crawl Space R-Value |
| 1 – 3 (Warmer) | R30–R49 | R19–R38 | R13 | No insulation required | No insulation required | R5 (Zone 3) |
| 4 (Moderate) | R60 | R49 | R13 | R10 | R10 | R10 |
| 4-Marine & 5 (Moderate to Cooler) | R60 | R49 | R20 | R10 (Zone 4 marine and 5) | R10 | R10 |
| 6 (Colder) | R60 | R49 | R20 | R15 | R10 | R10 |
| 7 & 8 (Very Cold & Subarctic) | R60 | R49 | R21 | R15 | R10 | R10 |
Need a more detailed table? The IECC and IRC insulation requirements for new homes.