What is a good R-value for insulation?

A good R-value for insulation depends on where the insulation is installed and what climate zone you live in, because different building assemblies have different code requirements and cost-benefit points. For attic floors, a good R-value is R-38 in hot southern zones and R-49 to R-60 in mixed and cold northern zones, which typically requires 13 to 18 inches of blown insulation. For walls, a good R-value is R-13 to R-15 for 2x4 walls and R-20 to R-23 for 2x6 walls with cavity insulation alone, plus R-5 to R-10 of continuous exterior foam for high-performance homes to reach R-20 to R-30 total. For floors over crawlspaces, R-19 to R-30 is good, and for basement walls R-10 to R-15 continuous is good. For cathedral ceilings with limited space, R-30 to R-38 is good. The concept of good also includes air sealing, because even R-60 with air leaks performs poorly. A good overall strategy is to meet or slightly exceed IECC code minimums for your zone, ensure insulation is installed without compression or gaps, and prioritize air sealing before adding more R-value beyond R-60 where diminishing returns make additional inches less valuable.