R-13 vs R-19 vs R-30 Insulation: Which Do You Need?

R-value measures resistance to heat flow, and the right number depends on where it's going, not just your climate. R-13 is sized for standard 2×4 wall framing (3.5 inches deep); R-19 is sized for 2×6 framing (5.5 inches deep) and used in colder climates or energy-code-driven builds.

Attics use higher values entirely — R-30 to R-38 is typical, since there's no framing-depth constraint and attics are the single biggest source of heat loss/gain in most homes. Check your local energy code for the actual minimum in your climate zone rather than guessing.

The Insulation Calculator lets you pick the R-value preset that matches your project and converts straight to a bag count.

Many current energy codes also call for continuous rigid foam insulation on the exterior of the wall sheathing, in addition to batts between the studs. This eliminates the thermal bridging that happens where studs interrupt the batt insulation, and is increasingly required rather than optional in colder climate zones.