Code-minimum R-values by climate zone for attics, walls, floors, crawl spaces and basements — 2021 vs older IECC editions, and what each means in inches. This guide is part of the Dixon App Studio blog — practical, no-fluff articles for builders, freelancers, home cooks, and sports fans. Read more guides on the blog index, browse our full app lineup, or use one of our free online converters whenever you need a quick answer.
Under the 2021 IECC: R-30 in climate zone 1, R-49 in zones 2–3 and R-60 in zones 4–8. Under the 2012–2018 editions it is R-30, R-38 and R-49 for the same groups of zones.
For a wood-frame wall cavity under the 2021 IECC: R-13 in zones 1–2, R-20 in zones 3–6 and R-21 in zones 7–8, with continuous exterior insulation added in the colder zones. Check Table R402.1.3 for the cavity + board options in your zone.
About 17.1 inches of blown cellulose (settled; blown about 11% deeper) or 24 inches of blown fiberglass.
Not with standard fiberglass batts, which top out near R-17 in 5.5 inches. High-density R-21 batts, R-23 mineral wool batts or dense-packed cellulose all reach it.
Yes, every calculator is free on Android with no signup, and the same calculators run in any browser at smartinsulationcalculator.com. The app is Android-only, on Google Play; on iPhone, Roofing Calculator & Estimator adds insulation tools in its next update.
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