Attic Insulation R-Value: How Much Do You Need?
Short answer: ENERGY STAR recommends a total attic insulation level of R60 in most of the US (climate zones 4–8), R49 in the warm South (zones 2–3), and R30 in zone 1 (South Florida, Hawaii and the territories). The recommendations are based on the 2021 International Energy Conservation Code.
To find how many inches to add on top of what you already have, use the insulation calculator.
Recommended attic R-values (ENERGY STAR)
| Climate zone | Uninsulated attic | Attic with 3–4 in already |
|---|---|---|
| 1 | R30 | Add R25 |
| 2–3 | R49 | Add R38 |
| 4–8 | R60 | Add R49 |
How many inches is that?
The Department of Energy’s rule of thumb for R-value per inch: about 2.5 for loose fiberglass, 3.7 for cellulose, 2.8 for rock wool and 3.2 for fiberglass batts. In an empty attic:
| Target | Blown cellulose | Blown fiberglass | Fiberglass batts |
|---|---|---|---|
| R30 | 8.1 in | 12 in | 9.4 in |
| R49 | 13.2 in | 19.6 in | 15.3 in |
| R60 | 16.2 in | 24 in | 18.8 in |
Products vary; the bag or batt label gives the exact depth for each R-value.
What R-value do I have now?
Measure the depth in a few places and multiply by the figure for your insulation: 6 inches of loose fiberglass is about R15, and 6 inches of cellulose about R22. If you see shiny, pebble-like granules, it may be vermiculite, which can contain asbestos: don’t disturb it, and have it tested.
Before you add insulation
- Seal air leaks around lights, pipes, wires and the attic hatch first.
- Keep soffit vents clear with baffles.
- Keep clear of chimneys, flues and recessed lights not rated for contact with insulation.
Common questions
Is R30 enough for an attic?
Only in climate zone 1. Most of the US is zone 4 or higher, where ENERGY STAR recommends R60.
How many inches is R38?
About 10 inches of cellulose, 15 inches of loose fiberglass, or 12 inches of fiberglass batts.