Standard: International Energy Conservation Code 2021 — climate zone 4 baseline (much of the temperate US).
Required R-values (zone 4)
- Exterior wall: R-20
- Roof: R-49
- Floor: R-30
Metric equivalent: U-0.30 / U-0.15 / U-0.30 W/m²K.
Climate
Heating Degree Days (HDD): 4,500 (US average for IECC zone 4).
Typical energy price (for savings estimation)
Electricity: ~$0.15/kWh.
R-value targets vary by climate zone (1–8). State-by-state details: energy.gov/energysaver/insulation.
These values are used as defaults in the insulation calculator — you can override the energy price field.