R-20 vs R-30 Insulation: Which Do You Need? Choosing between R-20 vs R-30 insulation comes down to climate, cavity depth, heating fuel and whether you’re renovating or building new. This article compares the two R-values, shows typical material thicknesses, and gives clear retrofit and new-build guidance so budget-conscious DIY builders can pick the right target and avoid common mistakes. Expect practical thickness examples, assembly trade-offs, and step-by-step retrofit tips you can use on a tiny house, attic or conventional framed wall. TL;DR: - R-20 provides a reasonable thermal barrier in mild climates or shallow cavities; it’s about 33% less R than R-30 and often fits a 2x6 wall or modest attic depth. - R-30 gives roughly 50% more R-value than R-20 (30 vs 20) and is a common minimum for attic floors and cold-climate upgrades — choose it if you have enough depth or can add continuous exterior foam. - If you’re retrofit-limited on depth, use dense-pack cellulose, layer with rigid fo...