Insulation Materials and R-Values
Thermal insulation slows heat transfer through building envelope assemblies, reducing heating and cooling energy consumption. The R-value measures thermal resistance, with higher values indicating better insulation performance. Fiberglass batts with R-values of R-13 for 2×4 walls and R-19 for 2×6 walls are the most common insulation type. Blown-in cellulose with R-3.7 per inch offers better air sealing properties than fiberglass. Spray foam insulation achieves the highest R-value per inch at R-6 to R-7 for closed-cell foam and R-3.5 for open-cell foam.
The International Energy Conservation Code specifies minimum insulation requirements based on climate zone. Zone 4 requires R-20 wall insulation and R-49 attic insulation. Zone 6 requires R-20+5 wall insulation and R-60 attic insulation. Continuous insulation on the exterior of the wall assembly reduces thermal bridging through framing members, which can reduce effective wall R-value by 15 to 25 percent.