Insulation & Air Quality
Insulation R-Value Chart: Recommended R-Values by Climate Zone
Attics need about R-30 to R-49 in the warmest zones and R-49 to R-60 in most of the country. Wood-framed walls range from R-13 in hot climates to R-20 plus continuous insulation in cold ones, and floors over unheated space need about R-13 to R-30. Your climate zone sets the target; the insulation type sets how thick it has to be.
Find your climate zone
The International Energy Conservation Code (IECC) and the DOE divide the US into eight climate zones, from hot to very cold.
| Zone | Example areas |
|---|---|
| 1 | South Florida, Hawaii, Puerto Rico |
| 2 | Gulf Coast, central and south Texas, southern Arizona, central Florida |
| 3 | Southeast, north Texas, Oklahoma, southern California, Las Vegas |
| 4 | Mid-Atlantic, Kentucky, Missouri, Kansas, Pacific Northwest coast (marine), New Mexico |
| 5 | Lower Midwest, Pennsylvania, southern New England, Colorado, Utah |
| 6 | Wisconsin, Minnesota (south), Vermont, Montana, upstate New York |
| 7 | Northern Minnesota, Michigan's Upper Peninsula, high mountains |
| 8 | Interior and northern Alaska |
Zone maps follow county lines, so check your county in the IECC or DOE zone map before buying materials.
Recommended R-values by climate zone
| Zone | Attic, uninsulated (DOE retrofit) | Ceiling, new build (IECC 2021) | Wood-frame wall, new build (IECC 2021) | Floor over unheated space (DOE) |
|---|---|---|---|---|
| 1 | R-30 to R-49 | R-30 | R-13 | R-13 |
| 2 | R-30 to R-60 | R-49 | R-13 | R-13 to R-19 |
| 3 | R-30 to R-60 | R-49 | R-20, or R-13 + R-5 continuous | R-19 to R-25 |
| 4 | R-38 to R-60 | R-60 | R-20 + R-5 ci, or R-13 + R-10 ci | R-25 to R-30 |
| 5 | R-49 to R-60 | R-60 | R-20 + R-5 ci, or R-13 + R-10 ci | R-25 to R-30 |
| 6 | R-49 to R-60 | R-60 | R-20 + R-5 ci, or R-13 + R-10 ci | R-25 to R-30 |
| 7–8 | R-49 to R-60 | R-60 | R-20 + R-5 ci, or R-13 + R-10 ci | R-25 to R-30 |
"ci" means continuous insulation, such as rigid foam or mineral wool board over the sheathing, which is not interrupted by studs. The IECC figures are prescriptive minimums for new construction; many states and cities adopt an older or amended edition, so your local code may differ. The DOE retrofit ranges are guidance for existing homes. If your attic already has 3 to 4 inches of insulation, the DOE suggests adding roughly R-25 to R-49 depending on zone.
R-value per inch and thickness needed
| Insulation type | R per inch (typical) | Inches for R-38 | Inches for R-60 |
|---|---|---|---|
| Blown fiberglass (loose fill) | 2.2–2.9 | 13–17 | 21–27 |
| Blown cellulose | 3.2–3.8 | 10–12 | 16–19 |
| Fiberglass batt | 2.9–4.3 | About 10–12 (R-38 batt) | Two layers |
| Mineral wool batt | 3.0–4.2 | 9–13 | 14–20 |
| Open-cell spray foam | 3.5–3.8 | 10–11 | 16–17 |
| Closed-cell spray foam | 6.0–7.0 | 5.5–6.5 | 8.5–10 |
| EPS rigid board | 3.6–4.2 | 9–10.5 | 14–17 |
| XPS rigid board | 5.0 | 7.6 | 12 |
| Polyiso rigid board | 5.6–6.5 | 6–7 | 9–11 |
Blown insulation settles over time, so manufacturers' coverage charts list both installed and settled thickness; go by the settled figure. Ruler markers stapled to attic joists make it easy to verify depth.
Where to insulate first
- Air seal the attic floor before adding insulation: top plates, plumbing and wiring holes, recessed lights rated for contact, and the attic hatch.
- Attic insulation: usually the cheapest R-value per dollar and the biggest single gain in older homes.
- Rim joists and basement walls: often uninsulated and leaky.
- Ducts in unconditioned spaces: seal with mastic and insulate to at least R-8 in attics.
- Floors over crawlspaces or garages.
- Walls: dense-pack cellulose can be blown into closed cavities, but walls are usually the costliest retrofit per R-value.
Keep loose-fill insulation away from soffit vents with baffles, and maintain clearances around chimneys, flues and non-IC-rated light fixtures. Knob-and-tube wiring should be inspected by an electrician before insulating around it.
Why the label number is not the whole story
Framing, gaps, compression and air leakage all reduce real-world performance below the nominal R-value. A 2×4 wall with R-13 batts performs closer to R-12 overall once studs and other layers are counted, as worked through in what is R-value. That is why the colder-zone wall requirements add continuous insulation outside the studs instead of only asking for thicker batts.
How insulation changes equipment size and bills
Better insulation lowers both the peak load and the seasonal energy use. When you replace a furnace or AC after an insulation upgrade, ask for a new load calculation rather than matching the old equipment size; the AC tonnage calculator and heating BTU calculator show how much the insulation setting moves the result. To estimate savings, compare before-and-after heat loss with the heating cost calculator.
Frequently asked questions
What R-value should my attic be?
About R-30 to R-49 in climate zone 1, and R-49 to R-60 across most of the rest of the US. Newer codes call for R-60 in zones 4 through 8.
Can a 2×4 wall reach R-20?
Not with cavity insulation alone. A 3.5-inch cavity holds about R-13 to R-15 with batts, or roughly R-21 to R-24 with closed-cell foam. Adding continuous exterior insulation is the usual route to higher wall performance.
Is there such a thing as too much attic insulation?
Not for heat loss, but returns diminish past about R-60, and insulation must not block soffit ventilation or bury non-IC-rated light fixtures.
Last reviewed 2026-10-28