Attic R-value by climate zone
Pick your IECC climate zone and read the labeled attic target R-value band — the number to aim for before you size bags, depth or cost.
Calculator
In IECC Zone 6, attics typically target R49–R60. Typical published values — confirm the current IECC/ENERGY STAR figure and your local energy code.
Formula
This is a labeled reference, not arithmetic. Pick a zone and the tool returns the published attic target R-value band from the IECC / ENERGY STAR recommendations:
Zones 1–3 → about R-30 to R-49 · Zones 4–8 → about R-49 to R-60
Colder zone, higher target. Once you have the band, feed it into the bag/depth calculator, the cost estimator, or the blown-in-vs-batt tool.
Worked example
Pick Zone 6 (cold — northern Midwest, northern New England): the labeled attic target is R-49 to R-60.
Aim for the upper end if you heat with an expensive fuel or the attic is your biggest heat-loss path; the lower end is the code-minimum floor. Then size it: 1,200 ft² to R-49 in blown fiberglass is about 43 bags at roughly 20 inches deep.
How to use the target
The band is a floor, not a ceiling. These are recommended targets; there is rarely a downside to going a little deeper in an attic, where extra inches are cheap and easy. The practical limit is depth over the top plate and keeping the eave baffles clear, not the R itself.
Attic gets the most R for a reason. Heat rises and the attic is usually the largest, easiest-to-reach uninsulated surface, so codes push attic R higher than walls or floors. That is why an attic target of R-49–R-60 sits next to a wall-cavity target of only R-13–R-21 in the same zone.
Confirm the current local code. IECC and ENERGY STAR figures are labeled planning typicals and get updated; your local jurisdiction may adopt a specific edition or amend it. Before you pull a permit, confirm the target with your building department — this reference gets you in the right range, not a code citation.
Air-seal first. R-value only pays off over an attic that is air-sealed at the top plates, penetrations and hatch. Piling insulation over leaky ceilings buys less than the R suggests. Set the target here, but treat air-sealing as step one.
Reference table
Labeled IECC / ENERGY STAR attic target R-value by climate zone.
| Climate zone | Attic target R |
|---|---|
| Zone 1 | R30–R49 |
| Zone 2 | R38–R49 |
| Zone 3 | R38–R49 |
| Zone 4 | R49–R60 |
| Zone 5 | R49–R60 |
| Zone 6 | R49–R60 |
| Zone 7 | R49–R60 |
| Zone 8 | R49–R60 |
Labeled planning typicals — confirm the current IECC/ENERGY STAR figure and your local energy code.