R-Value
A measure of thermal resistance indicating how well an insulation material resists heat flow—higher R-value means better insulation.
R-value quantifies a material's resistance to heat transfer by conduction. The higher the R-value, the more effective the insulation. Every inch of insulation material has a specific R-value per inch: fiberglass batts offer about R-3.5 per inch, closed-cell spray foam about R-6.5 per inch, and open-cell spray foam about R-3.7 per inch.
The required R-value for different parts of a home is dictated by local building codes and climate zone. The Department of Energy divides the US into zones 1–8; colder zones require higher R-values. Typical minimum requirements are R-13 to R-15 for exterior walls, R-30 to R-60 for attic floors, and R-10 to R-20 for basement walls depending on zone.
Proper insulation is one of the highest-return energy improvements available. Air sealing (plugging gaps) paired with adequate R-value can reduce heating and cooling costs by 15–30%. Insulation upgrades often qualify for federal tax credits and utility rebates.
Real-World Example
The energy auditor recommended upgrading the attic insulation from R-19 to R-49 to meet current code and reduce heating bills in the cold northern climate.