R-Value Calculator

How much insulation do you need?

R-value measures how well insulation resists heat flow — the higher the number, the slower heat escapes in winter or leaks in during summer. How much you need is set by your climate and by which part of the house you're insulating. Colder climates and attics call for the highest R-values; walls are capped by how deep the stud cavity is.

The recommendations on this page come from ENERGY STAR's Recommended Home Insulation R-Values, which ENERGY STAR aligns with the U.S. Department of Energy and the 2021 IECC climate-zone map.

Find your climate zone

The U.S. is split into eight IECC climate zones, numbered 1 (hottest) to 8 (subarctic). Zone boundaries follow county lines, so a single state can span two zones — use these as a starting point and confirm your county on the DOE climate-zone map.

• Zone 1–2: South Florida, south Texas, Hawaii, Gulf Coast.
• Zone 3: much of the Deep South, coastal California, Arizona's lower deserts.
• Zone 4: mid-Atlantic, Tennessee Valley, Pacific Northwest lowlands.
• Zone 5: the Midwest, New England coast, mountain West valleys.
• Zone 6: northern Midwest, upstate New York, northern New England.
• Zone 7: northern Minnesota, North Dakota, mountain-state highlands.
• Zone 8: interior Alaska.

Attic, walls, and floors are sized differently

• Attic / ceiling: the top priority. It loses the most heat and is usually the cheapest to top up — most zones want R49–R60.
• Exterior walls: limited by cavity depth. A 2×4 wall holds about R13–R15; hitting higher targets needs 2×6 framing or continuous exterior board.
• Floors over unheated space (crawlspaces, garages): R13 in the South up to R30 in cold zones.

Frequently asked questions

Can I just add more insulation to be safe? More R-value keeps helping, but with diminishing returns — going far past the recommendation for your zone rarely pays back its cost. Money is usually better spent air-sealing first, then insulating to the recommended level.

What does "R20+5" mean for a wall? It's an R20 cavity batt plus R5 of continuous rigid insulation over the studs (about R25 total). The continuous layer also breaks the thermal bridge through the framing, which a cavity batt alone can't do.

How many inches of insulation is R60? It depends on the material: roughly 16 inches of blown-in cellulose (≈ R3.7/inch) or a bit over 20 inches of loose-fill fibreglass (≈ R2.5–3/inch). Bag labels list the depth needed to reach each R-value.

Do these numbers apply to an existing house or only new construction? They're the recommended levels for both. In an existing home you're topping up toward the target; walls are the hardest to improve without opening them up, so many retrofits focus on the attic and floors first.

These are planning figures from ENERGY STAR's published recommendations. Local building codes may require more, and unusual assemblies (cathedral ceilings, conditioned crawlspaces) can differ — see our heating and cooling guides for detail.